| Message ID | 1424910661-26474-1-git-send-email-jorge.ramirez-ortiz@linaro.org |
|---|---|
| State | New |
| Headers | show |
On 02/26/2015 09:12 AM, Rob Herring wrote: > On Wed, Feb 25, 2015 at 6:31 PM, Jorge Ramirez-Ortiz > <jorge.ramirez-ortiz@linaro.org> wrote: >> Fix a race condition that happens when device_initcall(pl011_dma_initicall) >> is executed before all the devices have been probed - this issue was observed on >> an hisi_6220 SoC (HiKey board from Linaro). >> >> The deferred driver probing framework relies on late_initcall to trigger >> deferred probes so it is just possible that, even with a valid DMA driver ready >> to be loaded, we fail to synchronize with it. >> >> The proposed implementation delays probing of the DMA until the uart device is >> opened. As hw_init is invoked on port startup and port resume - but the DMA >> probe is only required once - we avoid calling multiple times using a new field >> in uart_amba_port to track this scenario. >> >> Signed-off-by: Jorge Ramirez-Ortiz <jorge.ramirez-ortiz@linaro.org> >> --- >> drivers/tty/serial/amba-pl011.c | 66 ++++++++++------------------------------- >> 1 file changed, 16 insertions(+), 50 deletions(-) >> >> diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c >> index 8d94c19..3501ccc 100644 >> --- a/drivers/tty/serial/amba-pl011.c >> +++ b/drivers/tty/serial/amba-pl011.c >> @@ -29,6 +29,7 @@ >> * and hooked into this driver. >> */ >> >> +#define pr_fmt(fmt) "amba-pl011: "fmt > You can drop this I think. why not keep it? it makes the trace more readable (if debug is enabled only) > >> #if defined(CONFIG_SERIAL_AMBA_PL011_CONSOLE) && defined(CONFIG_MAGIC_SYSRQ) >> #define SUPPORT_SYSRQ >> @@ -164,6 +165,7 @@ struct uart_amba_port { >> bool using_rx_dma; >> struct pl011_dmarx_data dmarx; >> struct pl011_dmatx_data dmatx; >> + bool dma_probed; >> #endif >> }; >> >> @@ -261,7 +263,7 @@ static void pl011_sgbuf_free(struct dma_chan *chan, struct pl011_sgbuf *sg, >> } >> } >> >> -static void pl011_dma_probe_initcall(struct device *dev, struct uart_amba_port *uap) >> +static void pl011_dma_probe(struct device *dev, struct uart_amba_port *uap) >> { >> /* DMA is the sole user of the platform data right now */ >> struct amba_pl011_data *plat = dev_get_platdata(uap->port.dev); >> @@ -275,9 +277,16 @@ static void pl011_dma_probe_initcall(struct device *dev, struct uart_amba_port * >> struct dma_chan *chan; >> dma_cap_mask_t mask; >> >> - chan = dma_request_slave_channel(dev, "tx"); >> + uap->dma_probed = true; > I would not set this to true in the case of EPROBE_DEFER. That way if > a DMA driver is loaded as a module some time later, DMA can be used. > We're not really using deferred probe here, but using it as an > indication that the UART is DMA capable. ok. yes there is no need for the consistency I wast talking about on my previous reply to RMK. that was rubbish. > >> + >> + chan = dma_request_slave_channel_reason(dev, "tx"); >> + if (IS_ERR(chan)) { >> + if (PTR_ERR(chan) == -EPROBE_DEFER) { >> + dev_warn(uap->port.dev, "DMA driver not ready\n"); I'll change the warn for an info since there will be future opportunities to load it. I see value on the user knowing he might have a chance to use the DMA capability. >> + return; >> + } >> + dev_info(uap->port.dev, "no OF or ACPI DMA data\n"); >> >> - if (!chan) { >> /* We need platform data */ >> if (!plat || !plat->dma_filter) { >> dev_info(uap->port.dev, "no DMA platform data\n"); >> @@ -383,54 +392,9 @@ static void pl011_dma_probe_initcall(struct device *dev, struct uart_amba_port * >> dev_info(uap->port.dev, "DMA channel RX %s\n", >> dma_chan_name(uap->dmarx.chan)); >> } >> -} >> - >> -#ifndef MODULE >> -/* >> - * Stack up the UARTs and let the above initcall be done at device >> - * initcall time, because the serial driver is called as an arch >> - * initcall, and at this time the DMA subsystem is not yet registered. >> - * At this point the driver will switch over to using DMA where desired. >> - */ >> -struct dma_uap { >> - struct list_head node; >> - struct uart_amba_port *uap; >> - struct device *dev; >> -}; >> - >> -static LIST_HEAD(pl011_dma_uarts); >> - >> -static int __init pl011_dma_initcall(void) >> -{ >> - struct list_head *node, *tmp; >> - >> - list_for_each_safe(node, tmp, &pl011_dma_uarts) { >> - struct dma_uap *dmau = list_entry(node, struct dma_uap, node); >> - pl011_dma_probe_initcall(dmau->dev, dmau->uap); >> - list_del(node); >> - kfree(dmau); >> - } >> - return 0; >> -} >> - >> -device_initcall(pl011_dma_initcall); >> >> -static void pl011_dma_probe(struct device *dev, struct uart_amba_port *uap) >> -{ >> - struct dma_uap *dmau = kzalloc(sizeof(struct dma_uap), GFP_KERNEL); >> - if (dmau) { >> - dmau->uap = uap; >> - dmau->dev = dev; >> - list_add_tail(&dmau->node, &pl011_dma_uarts); >> - } >> + return; > You don't need an explicit return. yes, not sure how that came in. > >> } >> -#else >> -static void pl011_dma_probe(struct device *dev, struct uart_amba_port *uap) >> -{ >> - pl011_dma_probe_initcall(dev, uap); >> -} >> -#endif >> -interviewing >> static void pl011_dma_remove(struct uart_amba_port *uap) >> { >> /* TODO: remove the initcall if it has not yet executed */ >> @@ -1548,6 +1512,9 @@ static int pl011_hwinit(struct uart_port *port) >> uap->im = readw(uap->port.membase + UART011_IMSC); >> writew(UART011_RTIM | UART011_RXIM, uap->port.membase + UART011_IMSC); >> >> + if (!uap->dma_probed) >> + pl011_dma_probe(uap->port.dev, uap); >> + >> if (dev_get_platdata(uap->port.dev)) { >> struct amba_pl011_data *plat; >> >> @@ -2218,7 +2185,6 @@ static int pl011_probe(struct amba_device *dev, const struct amba_id *id) >> uap->port.ops = &amba_pl011_pops; >> uap->port.flags = UPF_BOOT_AUTOCONF; >> uap->port.line = i; >> - pl011_dma_probe(&dev->dev, uap); >> >> /* Ensure interrupts from this UART are masked and cleared */ >> writew(0, uap->port.membase + UART011_IMSC); >> -- >> 1.9.1 >>
diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c index 8d94c19..3501ccc 100644 --- a/drivers/tty/serial/amba-pl011.c +++ b/drivers/tty/serial/amba-pl011.c @@ -29,6 +29,7 @@ * and hooked into this driver. */ +#define pr_fmt(fmt) "amba-pl011: "fmt #if defined(CONFIG_SERIAL_AMBA_PL011_CONSOLE) && defined(CONFIG_MAGIC_SYSRQ) #define SUPPORT_SYSRQ @@ -164,6 +165,7 @@ struct uart_amba_port { bool using_rx_dma; struct pl011_dmarx_data dmarx; struct pl011_dmatx_data dmatx; + bool dma_probed; #endif }; @@ -261,7 +263,7 @@ static void pl011_sgbuf_free(struct dma_chan *chan, struct pl011_sgbuf *sg, } } -static void pl011_dma_probe_initcall(struct device *dev, struct uart_amba_port *uap) +static void pl011_dma_probe(struct device *dev, struct uart_amba_port *uap) { /* DMA is the sole user of the platform data right now */ struct amba_pl011_data *plat = dev_get_platdata(uap->port.dev); @@ -275,9 +277,16 @@ static void pl011_dma_probe_initcall(struct device *dev, struct uart_amba_port * struct dma_chan *chan; dma_cap_mask_t mask; - chan = dma_request_slave_channel(dev, "tx"); + uap->dma_probed = true; + + chan = dma_request_slave_channel_reason(dev, "tx"); + if (IS_ERR(chan)) { + if (PTR_ERR(chan) == -EPROBE_DEFER) { + dev_warn(uap->port.dev, "DMA driver not ready\n"); + return; + } + dev_info(uap->port.dev, "no OF or ACPI DMA data\n"); - if (!chan) { /* We need platform data */ if (!plat || !plat->dma_filter) { dev_info(uap->port.dev, "no DMA platform data\n"); @@ -383,54 +392,9 @@ static void pl011_dma_probe_initcall(struct device *dev, struct uart_amba_port * dev_info(uap->port.dev, "DMA channel RX %s\n", dma_chan_name(uap->dmarx.chan)); } -} - -#ifndef MODULE -/* - * Stack up the UARTs and let the above initcall be done at device - * initcall time, because the serial driver is called as an arch - * initcall, and at this time the DMA subsystem is not yet registered. - * At this point the driver will switch over to using DMA where desired. - */ -struct dma_uap { - struct list_head node; - struct uart_amba_port *uap; - struct device *dev; -}; - -static LIST_HEAD(pl011_dma_uarts); - -static int __init pl011_dma_initcall(void) -{ - struct list_head *node, *tmp; - - list_for_each_safe(node, tmp, &pl011_dma_uarts) { - struct dma_uap *dmau = list_entry(node, struct dma_uap, node); - pl011_dma_probe_initcall(dmau->dev, dmau->uap); - list_del(node); - kfree(dmau); - } - return 0; -} - -device_initcall(pl011_dma_initcall); -static void pl011_dma_probe(struct device *dev, struct uart_amba_port *uap) -{ - struct dma_uap *dmau = kzalloc(sizeof(struct dma_uap), GFP_KERNEL); - if (dmau) { - dmau->uap = uap; - dmau->dev = dev; - list_add_tail(&dmau->node, &pl011_dma_uarts); - } + return; } -#else -static void pl011_dma_probe(struct device *dev, struct uart_amba_port *uap) -{ - pl011_dma_probe_initcall(dev, uap); -} -#endif - static void pl011_dma_remove(struct uart_amba_port *uap) { /* TODO: remove the initcall if it has not yet executed */ @@ -1548,6 +1512,9 @@ static int pl011_hwinit(struct uart_port *port) uap->im = readw(uap->port.membase + UART011_IMSC); writew(UART011_RTIM | UART011_RXIM, uap->port.membase + UART011_IMSC); + if (!uap->dma_probed) + pl011_dma_probe(uap->port.dev, uap); + if (dev_get_platdata(uap->port.dev)) { struct amba_pl011_data *plat; @@ -2218,7 +2185,6 @@ static int pl011_probe(struct amba_device *dev, const struct amba_id *id) uap->port.ops = &amba_pl011_pops; uap->port.flags = UPF_BOOT_AUTOCONF; uap->port.line = i; - pl011_dma_probe(&dev->dev, uap); /* Ensure interrupts from this UART are masked and cleared */ writew(0, uap->port.membase + UART011_IMSC);
Fix a race condition that happens when device_initcall(pl011_dma_initicall) is executed before all the devices have been probed - this issue was observed on an hisi_6220 SoC (HiKey board from Linaro). The deferred driver probing framework relies on late_initcall to trigger deferred probes so it is just possible that, even with a valid DMA driver ready to be loaded, we fail to synchronize with it. The proposed implementation delays probing of the DMA until the uart device is opened. As hw_init is invoked on port startup and port resume - but the DMA probe is only required once - we avoid calling multiple times using a new field in uart_amba_port to track this scenario. Signed-off-by: Jorge Ramirez-Ortiz <jorge.ramirez-ortiz@linaro.org> --- drivers/tty/serial/amba-pl011.c | 66 ++++++++++------------------------------- 1 file changed, 16 insertions(+), 50 deletions(-)