| Message ID | 20220623080344.783549-3-saravanak@google.com |
|---|---|
| State | Superseded |
| Headers | show |
| Series | Fix console probe delay due to fw_devlink | expand |
On Thu, Jun 23, 2022 at 12:04:21PM +0200, sascha hauer wrote: > On Thu, Jun 23, 2022 at 01:03:43AM -0700, Saravana Kannan wrote: ... > I wonder if it wouldn't be a better approach to just probe all devices > and record the device(node) they are waiting on. Then you know that you > don't need to probe them again until the device they are waiting for > is available. There may be no device, but resource. And we become again to the something like deferred probe ugly hack. The real solution is to rework device driver model in the kernel that it will create a graph of dependencies and then simply follow it. But actually it should be more than 1 graph, because there are resources and there are power, clock and resets that may be orthogonal to the higher dependencies (like driver X provides a resource to driver Y).
On Thu, Jun 23, 2022 at 6:39 PM Andy Shevchenko <andriy.shevchenko@linux.intel.com> wrote: > > On Thu, Jun 23, 2022 at 12:04:21PM +0200, sascha hauer wrote: > > On Thu, Jun 23, 2022 at 01:03:43AM -0700, Saravana Kannan wrote: > > ... > > > I wonder if it wouldn't be a better approach to just probe all devices > > and record the device(node) they are waiting on. Then you know that you > > don't need to probe them again until the device they are waiting for > > is available. > > There may be no device, but resource. And we become again to the something like > deferred probe ugly hack. > > The real solution is to rework device driver model in the kernel that it will > create a graph of dependencies and then simply follow it. But actually it should > be more than 1 graph, because there are resources and there are power, clock and > resets that may be orthogonal to the higher dependencies (like driver X provides > a resource to driver Y). There is one graph, or it wouldn't be possible to shut down the system orderly. The problem is that this graph is generally dynamic, especially during system init, and following dependencies in transient states is generally hard. Device links allow the already known dependencies to be recorded and taken into account later, so we already have a graph for those. The unknown dependencies obviously cannot be used for creating a graph of any sort, though, and here we are in the business of guessing what the unknown dependencies may be IIUC.
On Thu, Jun 23, 2022 at 3:05 AM sascha hauer <sha@pengutronix.de> wrote: > > On Thu, Jun 23, 2022 at 01:03:43AM -0700, Saravana Kannan wrote: > > Commit 71066545b48e ("driver core: Set fw_devlink.strict=1 by default") > > enabled iommus and dmas dependency enforcement by default. On some > > systems, this caused the console device's probe to get delayed until the > > deferred_probe_timeout expires. > > > > We need consoles to work as soon as possible, so mark the console device > > node with FWNODE_FLAG_BEST_EFFORT so that fw_delink knows not to delay > > the probe of the console device for suppliers without drivers. The > > driver can then make the decision on where it can probe without those > > suppliers or defer its probe. > > > > Fixes: 71066545b48e ("driver core: Set fw_devlink.strict=1 by default") > > Reported-by: Sascha Hauer <sha@pengutronix.de> > > Reported-by: Peng Fan <peng.fan@nxp.com> > > Signed-off-by: Saravana Kannan <saravanak@google.com> > > Tested-by: Peng Fan <peng.fan@nxp.com> > > --- > > drivers/of/base.c | 2 ++ > > 1 file changed, 2 insertions(+) > > > > diff --git a/drivers/of/base.c b/drivers/of/base.c > > index d4f98c8469ed..a19cd0c73644 100644 > > --- a/drivers/of/base.c > > +++ b/drivers/of/base.c > > @@ -1919,6 +1919,8 @@ void of_alias_scan(void * (*dt_alloc)(u64 size, u64 align)) > > of_property_read_string(of_aliases, "stdout", &name); > > if (name) > > of_stdout = of_find_node_opts_by_path(name, &of_stdout_options); > > + if (of_stdout) > > + of_stdout->fwnode.flags |= FWNODE_FLAG_BEST_EFFORT; > > The device given in the stdout-path property doesn't necessarily have to > be consistent with the console= parameter. The former is usually > statically set in the device trees contained in the kernel while the > latter is dynamically set by the bootloader. So if you change the > console uart in the bootloader then you'll still run into this trap. > > It's problematic to consult only the device tree for dependencies. I > found several examples of drivers in the tree for which dma support > is optional. They use it if they can, but continue without it when > not available. "hwlock" is another property which consider several > drivers as optional. Also consider SoCs in early upstreaming phases > when the device tree is merged with "dmas" or "hwlock" properties, > but the corresponding drivers are not yet upstreamed. It's not nice > to defer probing of all these devices for a long time. > > I wonder if it wouldn't be a better approach to just probe all devices > and record the device(node) they are waiting on. Then you know that you > don't need to probe them again until the device they are waiting for > is available. That actually breaks things in a worse sense. There are cases where the consumer driver is built in and the optional supplier driver is loaded at boot. Without fw_devlink and the deferred probe timeout, we end up probing the consumer with limited functionality. With the current setup, sure we delay some probes a bit but at least everything works with the right functionality. And you can reduce or remove the delay if you want to optimize it. -Saravana
On Thu, Jun 23, 2022 at 9:39 AM Andy Shevchenko <andriy.shevchenko@linux.intel.com> wrote: > > On Thu, Jun 23, 2022 at 12:04:21PM +0200, sascha hauer wrote: > > On Thu, Jun 23, 2022 at 01:03:43AM -0700, Saravana Kannan wrote: > > ... > > > I wonder if it wouldn't be a better approach to just probe all devices > > and record the device(node) they are waiting on. Then you know that you > > don't need to probe them again until the device they are waiting for > > is available. > > There may be no device, but resource. And we become again to the something like > deferred probe ugly hack. > > The real solution is to rework device driver model in the kernel that it will > create a graph of dependencies and then simply follow it. But actually it should > be more than 1 graph, because there are resources and there are power, clock and > resets that may be orthogonal to the higher dependencies (like driver X provides > a resource to driver Y). We already do this with fw_devlink for DT based systems and we do effectively just probe the devices in graph order (by deferring any attempts that happen too early and before it even gets to the driver). The problem is the knowledge of what's considered an optional vs mandatory dependency and that's affected by the global state of driver support in the kernel. -Saravana
Hello Saravana, On 23.06.22 19:26, Saravana Kannan wrote: > On Thu, Jun 23, 2022 at 3:05 AM sascha hauer <sha@pengutronix.de> wrote: >> >> On Thu, Jun 23, 2022 at 01:03:43AM -0700, Saravana Kannan wrote: >>> Commit 71066545b48e ("driver core: Set fw_devlink.strict=1 by default") >>> enabled iommus and dmas dependency enforcement by default. On some >>> systems, this caused the console device's probe to get delayed until the >>> deferred_probe_timeout expires. >>> >>> We need consoles to work as soon as possible, so mark the console device >>> node with FWNODE_FLAG_BEST_EFFORT so that fw_delink knows not to delay >>> the probe of the console device for suppliers without drivers. The >>> driver can then make the decision on where it can probe without those >>> suppliers or defer its probe. >>> >>> Fixes: 71066545b48e ("driver core: Set fw_devlink.strict=1 by default") >>> Reported-by: Sascha Hauer <sha@pengutronix.de> >>> Reported-by: Peng Fan <peng.fan@nxp.com> >>> Signed-off-by: Saravana Kannan <saravanak@google.com> >>> Tested-by: Peng Fan <peng.fan@nxp.com> >>> --- >>> drivers/of/base.c | 2 ++ >>> 1 file changed, 2 insertions(+) >>> >>> diff --git a/drivers/of/base.c b/drivers/of/base.c >>> index d4f98c8469ed..a19cd0c73644 100644 >>> --- a/drivers/of/base.c >>> +++ b/drivers/of/base.c >>> @@ -1919,6 +1919,8 @@ void of_alias_scan(void * (*dt_alloc)(u64 size, u64 align)) >>> of_property_read_string(of_aliases, "stdout", &name); >>> if (name) >>> of_stdout = of_find_node_opts_by_path(name, &of_stdout_options); >>> + if (of_stdout) >>> + of_stdout->fwnode.flags |= FWNODE_FLAG_BEST_EFFORT; >> >> The device given in the stdout-path property doesn't necessarily have to >> be consistent with the console= parameter. The former is usually >> statically set in the device trees contained in the kernel while the >> latter is dynamically set by the bootloader. So if you change the >> console uart in the bootloader then you'll still run into this trap. >> >> It's problematic to consult only the device tree for dependencies. I >> found several examples of drivers in the tree for which dma support >> is optional. They use it if they can, but continue without it when >> not available. "hwlock" is another property which consider several >> drivers as optional. Also consider SoCs in early upstreaming phases >> when the device tree is merged with "dmas" or "hwlock" properties, >> but the corresponding drivers are not yet upstreamed. It's not nice >> to defer probing of all these devices for a long time. >> >> I wonder if it wouldn't be a better approach to just probe all devices >> and record the device(node) they are waiting on. Then you know that you >> don't need to probe them again until the device they are waiting for >> is available. > > That actually breaks things in a worse sense. There are cases where > the consumer driver is built in and the optional supplier driver is > loaded at boot. Without fw_devlink and the deferred probe timeout, we > end up probing the consumer with limited functionality. With the > current setup, sure we delay some probes a bit but at least everything > works with the right functionality. And you can reduce or remove the > delay if you want to optimize it. I have a system that doesn't use stdout-path and has the bootloader set console= either to ttynull when secure booting or to an UART when booting normally. How would I optimize the kernel to avoid my UART being loaded after DMA controller probe without touching the bootloader? Cheers, Ahmad > > -Saravana > >
On Thu, Jun 23, 2022 at 10:36 AM Ahmad Fatoum <a.fatoum@pengutronix.de> wrote: > > Hello Saravana, > > On 23.06.22 19:26, Saravana Kannan wrote: > > On Thu, Jun 23, 2022 at 3:05 AM sascha hauer <sha@pengutronix.de> wrote: > >> > >> On Thu, Jun 23, 2022 at 01:03:43AM -0700, Saravana Kannan wrote: > >>> Commit 71066545b48e ("driver core: Set fw_devlink.strict=1 by default") > >>> enabled iommus and dmas dependency enforcement by default. On some > >>> systems, this caused the console device's probe to get delayed until the > >>> deferred_probe_timeout expires. > >>> > >>> We need consoles to work as soon as possible, so mark the console device > >>> node with FWNODE_FLAG_BEST_EFFORT so that fw_delink knows not to delay > >>> the probe of the console device for suppliers without drivers. The > >>> driver can then make the decision on where it can probe without those > >>> suppliers or defer its probe. > >>> > >>> Fixes: 71066545b48e ("driver core: Set fw_devlink.strict=1 by default") > >>> Reported-by: Sascha Hauer <sha@pengutronix.de> > >>> Reported-by: Peng Fan <peng.fan@nxp.com> > >>> Signed-off-by: Saravana Kannan <saravanak@google.com> > >>> Tested-by: Peng Fan <peng.fan@nxp.com> > >>> --- > >>> drivers/of/base.c | 2 ++ > >>> 1 file changed, 2 insertions(+) > >>> > >>> diff --git a/drivers/of/base.c b/drivers/of/base.c > >>> index d4f98c8469ed..a19cd0c73644 100644 > >>> --- a/drivers/of/base.c > >>> +++ b/drivers/of/base.c > >>> @@ -1919,6 +1919,8 @@ void of_alias_scan(void * (*dt_alloc)(u64 size, u64 align)) > >>> of_property_read_string(of_aliases, "stdout", &name); > >>> if (name) > >>> of_stdout = of_find_node_opts_by_path(name, &of_stdout_options); > >>> + if (of_stdout) > >>> + of_stdout->fwnode.flags |= FWNODE_FLAG_BEST_EFFORT; > >> > >> The device given in the stdout-path property doesn't necessarily have to > >> be consistent with the console= parameter. The former is usually > >> statically set in the device trees contained in the kernel while the > >> latter is dynamically set by the bootloader. So if you change the > >> console uart in the bootloader then you'll still run into this trap. > >> > >> It's problematic to consult only the device tree for dependencies. I > >> found several examples of drivers in the tree for which dma support > >> is optional. They use it if they can, but continue without it when > >> not available. "hwlock" is another property which consider several > >> drivers as optional. Also consider SoCs in early upstreaming phases > >> when the device tree is merged with "dmas" or "hwlock" properties, > >> but the corresponding drivers are not yet upstreamed. It's not nice > >> to defer probing of all these devices for a long time. > >> > >> I wonder if it wouldn't be a better approach to just probe all devices > >> and record the device(node) they are waiting on. Then you know that you > >> don't need to probe them again until the device they are waiting for > >> is available. > > > > That actually breaks things in a worse sense. There are cases where > > the consumer driver is built in and the optional supplier driver is > > loaded at boot. Without fw_devlink and the deferred probe timeout, we > > end up probing the consumer with limited functionality. With the > > current setup, sure we delay some probes a bit but at least everything > > works with the right functionality. And you can reduce or remove the > > delay if you want to optimize it. > > I have a system that doesn't use stdout-path and has the bootloader > set console= either to ttynull when secure booting or to an UART > when booting normally. How would I optimize the kernel to avoid > my UART being loaded after DMA controller probe without touching > the bootloader? > Thanks for the report Ahmad. I think someone else reported a similar thing in another thread. I plan to take a look at it. It should be possible to find the device and set the flag for those devices too. -Saravana
On Thu, Jun 23, 2022 at 10:26:46AM -0700, Saravana Kannan wrote: > On Thu, Jun 23, 2022 at 3:05 AM sascha hauer <sha@pengutronix.de> wrote: > > > > On Thu, Jun 23, 2022 at 01:03:43AM -0700, Saravana Kannan wrote: > > > Commit 71066545b48e ("driver core: Set fw_devlink.strict=1 by default") > > > enabled iommus and dmas dependency enforcement by default. On some > > > systems, this caused the console device's probe to get delayed until the > > > deferred_probe_timeout expires. > > > > > > We need consoles to work as soon as possible, so mark the console device > > > node with FWNODE_FLAG_BEST_EFFORT so that fw_delink knows not to delay > > > the probe of the console device for suppliers without drivers. The > > > driver can then make the decision on where it can probe without those > > > suppliers or defer its probe. > > > > > > Fixes: 71066545b48e ("driver core: Set fw_devlink.strict=1 by default") > > > Reported-by: Sascha Hauer <sha@pengutronix.de> > > > Reported-by: Peng Fan <peng.fan@nxp.com> > > > Signed-off-by: Saravana Kannan <saravanak@google.com> > > > Tested-by: Peng Fan <peng.fan@nxp.com> > > > --- > > > drivers/of/base.c | 2 ++ > > > 1 file changed, 2 insertions(+) > > > > > > diff --git a/drivers/of/base.c b/drivers/of/base.c > > > index d4f98c8469ed..a19cd0c73644 100644 > > > --- a/drivers/of/base.c > > > +++ b/drivers/of/base.c > > > @@ -1919,6 +1919,8 @@ void of_alias_scan(void * (*dt_alloc)(u64 size, u64 align)) > > > of_property_read_string(of_aliases, "stdout", &name); > > > if (name) > > > of_stdout = of_find_node_opts_by_path(name, &of_stdout_options); > > > + if (of_stdout) > > > + of_stdout->fwnode.flags |= FWNODE_FLAG_BEST_EFFORT; > > > > The device given in the stdout-path property doesn't necessarily have to > > be consistent with the console= parameter. The former is usually > > statically set in the device trees contained in the kernel while the > > latter is dynamically set by the bootloader. So if you change the > > console uart in the bootloader then you'll still run into this trap. > > > > It's problematic to consult only the device tree for dependencies. I > > found several examples of drivers in the tree for which dma support > > is optional. They use it if they can, but continue without it when > > not available. "hwlock" is another property which consider several > > drivers as optional. Also consider SoCs in early upstreaming phases > > when the device tree is merged with "dmas" or "hwlock" properties, > > but the corresponding drivers are not yet upstreamed. It's not nice > > to defer probing of all these devices for a long time. > > > > I wonder if it wouldn't be a better approach to just probe all devices > > and record the device(node) they are waiting on. Then you know that you > > don't need to probe them again until the device they are waiting for > > is available. > > That actually breaks things in a worse sense. There are cases where > the consumer driver is built in and the optional supplier driver is > loaded at boot. Without fw_devlink and the deferred probe timeout, we > end up probing the consumer with limited functionality. With the > current setup, sure we delay some probes a bit but at least everything > works with the right functionality. And you can reduce or remove the > delay if you want to optimize it. We have optional and mandatory resources. In this situation a driver has to decide what to do. Either it continues with limited resources or it defers probing. Some drivers try to allocate the optional resources at open time so that they are able to use them once they are available. We could even think of an asynchronous callback into a driver when a resource becomes available. Whether we put this decision what is optional or not into the driver or in the framework doesn't make a difference to the problem, it is still the same: When a resource is not yet available we have no idea if and when it becomes available, if it's worth waiting for it or not. The difference is that with my proposal (which isn't actually mine but from my collegue Lucas) a driver can decide very fine grained how it wants to deal with the situation. With fw_devlink we try to put this intelligence into the framework and it seems there are quite some quirks necessary to get that running for everyone. Anyway, we have fw_devlink now and actually I think the dependency graph that we have with fw_devlink is quite nice to resolve the natural probe order. But why do we have to put an extra penalty on drivers whose resources are not yet available? Probe devices with complete resources as long as you find them, execute more initcalls as long as there are any, but when there are no more left, you could start probing devices with incomplete resources, why wait for another ten seconds? For me it's no problem when the UART probes late, we have earlycon which can be used to debug problems that arise before the UART probes, but what nags is the ten seconds delay. zero would be a much saner value for me. Sascha
On Thu, Jun 23, 2022 at 1:37 PM sascha hauer <sha@pengutronix.de> wrote: > > On Thu, Jun 23, 2022 at 10:26:46AM -0700, Saravana Kannan wrote: > > On Thu, Jun 23, 2022 at 3:05 AM sascha hauer <sha@pengutronix.de> wrote: > > > > > > On Thu, Jun 23, 2022 at 01:03:43AM -0700, Saravana Kannan wrote: > > > > Commit 71066545b48e ("driver core: Set fw_devlink.strict=1 by default") > > > > enabled iommus and dmas dependency enforcement by default. On some > > > > systems, this caused the console device's probe to get delayed until the > > > > deferred_probe_timeout expires. > > > > > > > > We need consoles to work as soon as possible, so mark the console device > > > > node with FWNODE_FLAG_BEST_EFFORT so that fw_delink knows not to delay > > > > the probe of the console device for suppliers without drivers. The > > > > driver can then make the decision on where it can probe without those > > > > suppliers or defer its probe. > > > > > > > > Fixes: 71066545b48e ("driver core: Set fw_devlink.strict=1 by default") > > > > Reported-by: Sascha Hauer <sha@pengutronix.de> > > > > Reported-by: Peng Fan <peng.fan@nxp.com> > > > > Signed-off-by: Saravana Kannan <saravanak@google.com> > > > > Tested-by: Peng Fan <peng.fan@nxp.com> > > > > --- > > > > drivers/of/base.c | 2 ++ > > > > 1 file changed, 2 insertions(+) > > > > > > > > diff --git a/drivers/of/base.c b/drivers/of/base.c > > > > index d4f98c8469ed..a19cd0c73644 100644 > > > > --- a/drivers/of/base.c > > > > +++ b/drivers/of/base.c > > > > @@ -1919,6 +1919,8 @@ void of_alias_scan(void * (*dt_alloc)(u64 size, u64 align)) > > > > of_property_read_string(of_aliases, "stdout", &name); > > > > if (name) > > > > of_stdout = of_find_node_opts_by_path(name, &of_stdout_options); > > > > + if (of_stdout) > > > > + of_stdout->fwnode.flags |= FWNODE_FLAG_BEST_EFFORT; > > > > > > The device given in the stdout-path property doesn't necessarily have to > > > be consistent with the console= parameter. The former is usually > > > statically set in the device trees contained in the kernel while the > > > latter is dynamically set by the bootloader. So if you change the > > > console uart in the bootloader then you'll still run into this trap. > > > > > > It's problematic to consult only the device tree for dependencies. I > > > found several examples of drivers in the tree for which dma support > > > is optional. They use it if they can, but continue without it when > > > not available. "hwlock" is another property which consider several > > > drivers as optional. Also consider SoCs in early upstreaming phases > > > when the device tree is merged with "dmas" or "hwlock" properties, > > > but the corresponding drivers are not yet upstreamed. It's not nice > > > to defer probing of all these devices for a long time. > > > > > > I wonder if it wouldn't be a better approach to just probe all devices > > > and record the device(node) they are waiting on. Then you know that you > > > don't need to probe them again until the device they are waiting for > > > is available. > > > > That actually breaks things in a worse sense. There are cases where > > the consumer driver is built in and the optional supplier driver is > > loaded at boot. Without fw_devlink and the deferred probe timeout, we > > end up probing the consumer with limited functionality. With the > > current setup, sure we delay some probes a bit but at least everything > > works with the right functionality. And you can reduce or remove the > > delay if you want to optimize it. > > We have optional and mandatory resources. In this situation a driver has > to decide what to do. Either it continues with limited resources or it > defers probing. Some drivers try to allocate the optional resources at > open time so that they are able to use them once they are available. We > could even think of an asynchronous callback into a driver when a > resource becomes available. Whether we put this decision what is > optional or not into the driver or in the framework doesn't make a > difference to the problem, it is still the same: When a resource is not > yet available we have no idea if and when it becomes available, if it's > worth waiting for it or not. > > The difference is that with my proposal (which isn't actually mine but > from my collegue Lucas) a driver can decide very fine grained how it > wants to deal with the situation. With fw_devlink we try to put this > intelligence into the framework and it seems there are quite some quirks > necessary to get that running for everyone. That's one possible solution, but for that to work, all drivers with optional suppliers would need to be changed to take advantage of this callback to work correctly when the optional suppliers become available. We could add this callback, but it would be a long time before the callback handles all/most cases of optional suppliers. One of the goals of fw_devlink is so that people can stop having to play initcall chicken where they try to tune their initcall levels wrt to the chain of suppliers to avoid probe failures or minimize deferred probed. Technically with deferred probes and proper error handling, people shouldn't have to play initcall chicken, but we still have a lot of those. Adding this callback is just going to make writing drivers even harder. And there are tons of drivers that can't do proper clean up and some drivers can't even be unbound once they are bound. Also, if I'm not mistaken (I could be), stuff like pinctrl is setup before we even get to driver->probe(). So when the pinctrl supplier becomes available, the driver would need to unbind fully and rebind. What if there's a current user of the device? > Anyway, we have fw_devlink now and actually I think the dependency graph > that we have with fw_devlink is quite nice to resolve the natural probe > order. But why do we have to put an extra penalty on drivers whose > resources are not yet available? Probe devices with complete resources > as long as you find them, execute more initcalls as long as there are > any, but when there are no more left, you could start probing devices > with incomplete resources, why wait for another ten seconds? The timeout is defining how long after the most recent module load that we give up waiting for more modules to be loaded. On a Pixel 6 with serial console output, the timeout of 5 seconds would work because the worst case gap between two module loads is ~2.8 seconds (so 5 seconds for some margin). The default is this high to accommodate slow storage devices where mounting all the filesystems can take time (think HDD or network FS). The default is configured for correctness so that we can maximize functionality across systems, but people can optimize for the specific case. > For me it's no problem when the UART probes late, we have earlycon which > can be used to debug problems that arise before the UART probes, but > what nags is the ten seconds delay. zero would be a much saner value for > me. Having said all that, I empathize with your annoyance at the delay. Open to ideas of making this better without making the default functionality worse. -Saravana
On Thu, Jun 23, 2022 at 12:04:21PM +0200, sascha hauer wrote: > On Thu, Jun 23, 2022 at 01:03:43AM -0700, Saravana Kannan wrote: > > Commit 71066545b48e ("driver core: Set fw_devlink.strict=1 by default") > > enabled iommus and dmas dependency enforcement by default. On some > > systems, this caused the console device's probe to get delayed until the > > deferred_probe_timeout expires. > > > > We need consoles to work as soon as possible, so mark the console device > > node with FWNODE_FLAG_BEST_EFFORT so that fw_delink knows not to delay > > the probe of the console device for suppliers without drivers. The > > driver can then make the decision on where it can probe without those > > suppliers or defer its probe. > > > > Fixes: 71066545b48e ("driver core: Set fw_devlink.strict=1 by default") > > Reported-by: Sascha Hauer <sha@pengutronix.de> > > Reported-by: Peng Fan <peng.fan@nxp.com> > > Signed-off-by: Saravana Kannan <saravanak@google.com> > > Tested-by: Peng Fan <peng.fan@nxp.com> > > --- > > drivers/of/base.c | 2 ++ > > 1 file changed, 2 insertions(+) > > > > diff --git a/drivers/of/base.c b/drivers/of/base.c > > index d4f98c8469ed..a19cd0c73644 100644 > > --- a/drivers/of/base.c > > +++ b/drivers/of/base.c > > @@ -1919,6 +1919,8 @@ void of_alias_scan(void * (*dt_alloc)(u64 size, u64 align)) > > of_property_read_string(of_aliases, "stdout", &name); > > if (name) > > of_stdout = of_find_node_opts_by_path(name, &of_stdout_options); > > + if (of_stdout) > > + of_stdout->fwnode.flags |= FWNODE_FLAG_BEST_EFFORT; > > The device given in the stdout-path property doesn't necessarily have to > be consistent with the console= parameter. The former is usually > statically set in the device trees contained in the kernel while the > latter is dynamically set by the bootloader. So if you change the > console uart in the bootloader then you'll still run into this trap. > > It's problematic to consult only the device tree for dependencies. I > found several examples of drivers in the tree for which dma support > is optional. They use it if they can, but continue without it when > not available. "hwlock" is another property which consider several > drivers as optional. Also consider SoCs in early upstreaming phases > when the device tree is merged with "dmas" or "hwlock" properties, > but the corresponding drivers are not yet upstreamed. It's not nice > to defer probing of all these devices for a long time. > > I wonder if it wouldn't be a better approach to just probe all devices > and record the device(node) they are waiting on. Then you know that you > don't need to probe them again until the device they are waiting for > is available. Can't we have a driver flag 'I have optional dependencies' that will trigger probe without all dependencies and then the driver can defer probe if required dependencies are not yet met. Rob
On Mon, Jun 27, 2022 at 10:50 AM Rob Herring <robh@kernel.org> wrote: > > On Thu, Jun 23, 2022 at 12:04:21PM +0200, sascha hauer wrote: > > On Thu, Jun 23, 2022 at 01:03:43AM -0700, Saravana Kannan wrote: > > > Commit 71066545b48e ("driver core: Set fw_devlink.strict=1 by default") > > > enabled iommus and dmas dependency enforcement by default. On some > > > systems, this caused the console device's probe to get delayed until the > > > deferred_probe_timeout expires. > > > > > > We need consoles to work as soon as possible, so mark the console device > > > node with FWNODE_FLAG_BEST_EFFORT so that fw_delink knows not to delay > > > the probe of the console device for suppliers without drivers. The > > > driver can then make the decision on where it can probe without those > > > suppliers or defer its probe. > > > > > > Fixes: 71066545b48e ("driver core: Set fw_devlink.strict=1 by default") > > > Reported-by: Sascha Hauer <sha@pengutronix.de> > > > Reported-by: Peng Fan <peng.fan@nxp.com> > > > Signed-off-by: Saravana Kannan <saravanak@google.com> > > > Tested-by: Peng Fan <peng.fan@nxp.com> > > > --- > > > drivers/of/base.c | 2 ++ > > > 1 file changed, 2 insertions(+) > > > > > > diff --git a/drivers/of/base.c b/drivers/of/base.c > > > index d4f98c8469ed..a19cd0c73644 100644 > > > --- a/drivers/of/base.c > > > +++ b/drivers/of/base.c > > > @@ -1919,6 +1919,8 @@ void of_alias_scan(void * (*dt_alloc)(u64 size, u64 align)) > > > of_property_read_string(of_aliases, "stdout", &name); > > > if (name) > > > of_stdout = of_find_node_opts_by_path(name, &of_stdout_options); > > > + if (of_stdout) > > > + of_stdout->fwnode.flags |= FWNODE_FLAG_BEST_EFFORT; > > > > The device given in the stdout-path property doesn't necessarily have to > > be consistent with the console= parameter. The former is usually > > statically set in the device trees contained in the kernel while the > > latter is dynamically set by the bootloader. So if you change the > > console uart in the bootloader then you'll still run into this trap. > > > > It's problematic to consult only the device tree for dependencies. I > > found several examples of drivers in the tree for which dma support > > is optional. They use it if they can, but continue without it when > > not available. "hwlock" is another property which consider several > > drivers as optional. Also consider SoCs in early upstreaming phases > > when the device tree is merged with "dmas" or "hwlock" properties, > > but the corresponding drivers are not yet upstreamed. It's not nice > > to defer probing of all these devices for a long time. > > > > I wonder if it wouldn't be a better approach to just probe all devices > > and record the device(node) they are waiting on. Then you know that you > > don't need to probe them again until the device they are waiting for > > is available. > > Can't we have a driver flag 'I have optional dependencies' that will > trigger probe without all dependencies and then the driver can defer > probe if required dependencies are not yet met. Haha... that's kinda what I'm working on right now. But named intentionally in a more limited sense of "I can't wait for the timeout" where fw_devlink will relax and allow the driver to probe (and have it make the call) once we hit late_initcall(). I'm explicitly limiting it to "timeout" because we don't want everyone adding this flag everytime they hit an issue. That'll beat the point of fw_devlink=on. Also, setting the flag for a driver to fix one system might break another system because in the other system the user might want to wait for the timeout because the supplier drivers would be loaded before the timeout. Another option is to restart the timer (if it hasn't expired) when filesystems get mounted (in addition to the current "when new driver gets registered). That way, we might be able to drop the timeout from 10s to 5s. -Saravana
On Thu, Jun 23, 2022 at 12:05 PM sascha hauer <sha@pengutronix.de> wrote: > Also consider SoCs in early upstreaming phases > when the device tree is merged with "dmas" or "hwlock" properties, > but the corresponding drivers are not yet upstreamed. It's not nice > to defer probing of all these devices for a long time. Actually this drives a truck through the entire approach in a way. It is perfectly legal to have a device tree with dmas specified but leave them unused in the operating system. DT just describes what hardware is there, it does not mandate that the OS implement drivers for all of it. This approach really needs that the resolution mechanism is aware of whether: 1. a driver exist for the resource at all so it will eventually resolve 2. if that driver is compiled in or module at all (IS_ENABLED()) 3. If the resource should be grabbed early or optionally later such as dmas for console UART Only then can the mechanism work in the generic case. Yours, Linus Walleij
diff --git a/drivers/of/base.c b/drivers/of/base.c index d4f98c8469ed..a19cd0c73644 100644 --- a/drivers/of/base.c +++ b/drivers/of/base.c @@ -1919,6 +1919,8 @@ void of_alias_scan(void * (*dt_alloc)(u64 size, u64 align)) of_property_read_string(of_aliases, "stdout", &name); if (name) of_stdout = of_find_node_opts_by_path(name, &of_stdout_options); + if (of_stdout) + of_stdout->fwnode.flags |= FWNODE_FLAG_BEST_EFFORT; } if (!of_aliases)
Commit 71066545b48e ("driver core: Set fw_devlink.strict=1 by default") enabled iommus and dmas dependency enforcement by default. On some systems, this caused the console device's probe to get delayed until the deferred_probe_timeout expires. We need consoles to work as soon as possible, so mark the console device node with FWNODE_FLAG_BEST_EFFORT so that fw_delink knows not to delay the probe of the console device for suppliers without drivers. The driver can then make the decision on where it can probe without those suppliers or defer its probe. Fixes: 71066545b48e ("driver core: Set fw_devlink.strict=1 by default") Reported-by: Sascha Hauer <sha@pengutronix.de> Reported-by: Peng Fan <peng.fan@nxp.com> Signed-off-by: Saravana Kannan <saravanak@google.com> Tested-by: Peng Fan <peng.fan@nxp.com> --- drivers/of/base.c | 2 ++ 1 file changed, 2 insertions(+)