[05/11] of: Ratify of_dma_configure() interface

From: Robin Murphy <robin.murphy@arm.com>


For various DMA masters not directly represented in DT, we pass the OF
node of their parent or bridge device as the master_np argument to
of_dma_configure(), such that they can inherit the appropriate DMA
configuration from whatever is described there. This creates an
ambiguity for properties which are not valid for a device itself but
only for its parent bus, since we don't know whether to start looking
for those at master_np or master_np->parent.

Fortunately, the de-facto interface since the prototype change in
1f5c69aa51f9 ("of: Move of_dma_configure() to device.c to help re-use")
is pretty clear-cut: either master_np is redundant with dev->of_node, or
dev->of_node is NULL and master_np is already the relevant parent. Let's
formally ratify that so we can start relying on it.

Signed-off-by: Robin Murphy <robin.murphy@arm.com>

Signed-off-by: Rob Herring <robh@kernel.org>

---
 drivers/of/device.c       | 12 ++++++++++--
 include/linux/of_device.h |  4 ++--
 2 files changed, 12 insertions(+), 4 deletions(-)

-- 
2.20.1

On Mon, Sep 30, 2019 at 8:32 AM Nicolas Saenz Julienne
<nsaenzjulienne@suse.de> wrote:
>

> On Mon, 2019-09-30 at 05:57 -0700, Christoph Hellwig wrote:

> > On Thu, Sep 26, 2019 at 07:24:49PM -0500, Rob Herring wrote:

> > > -int of_dma_configure(struct device *dev, struct device_node *np, bool

> > > force_dma)

> > > +int of_dma_configure(struct device *dev, struct device_node *parent, bool

> > > force_dma)

> >

> > This creates a > 80 char line.

> >

> > >  {

> > >     u64 dma_addr, paddr, size = 0;

> > >     int ret;

> > >     bool coherent;

> > >     unsigned long offset;

> > >     const struct iommu_ops *iommu;

> > > +   struct device_node *np;

> > >     u64 mask;

> > >

> > > +   np = dev->of_node;

> > > +   if (!np)

> > > +           np = parent;

> > > +   if (!np)

> > > +           return -ENODEV;

> >

> > I have to say I find the older calling convention simpler to understand.

> > If we want to enforce the invariant I'd rather do that explicitly:

> >

> >       if (dev->of_node && np != dev->of_node)

> >               return -EINVAL;

>

> As is, this would break Freescale Layerscape fsl-mc bus' dma_configure():


This may break PCI too for devices that have a DT node.

> static int fsl_mc_dma_configure(struct device *dev)

> {

>         struct device *dma_dev = dev;

>

>         while (dev_is_fsl_mc(dma_dev))

>                 dma_dev = dma_dev->parent;

>

>         return of_dma_configure(dev, dma_dev->of_node, 0);

> }

>

> But I think that with this series, given the fact that we now treat the lack of

> dma-ranges as a 1:1 mapping instead of an error, we could rewrite the function

> like this:


Now, I'm reconsidering allowing this abuse... It's better if the code
which understands the bus structure in DT for a specific bus passes in
the right thing. Maybe I should go back to Robin's version (below).
OTOH, the existing assumption that 'dma-ranges' was in the immediate
parent was an assumption on the bus structure which maybe doesn't
always apply.

diff --git a/drivers/of/device.c b/drivers/of/device.c
index a45261e21144..6951450bb8f3 100644
--- a/drivers/of/device.c
+++ b/drivers/of/device.c
@@ -98,12 +98,15 @@ int of_dma_configure(struct device *dev, struct
device_node *parent, bool force_
        u64 mask;

        np = dev->of_node;
-       if (!np)
-               np = parent;
+       if (np)
+               parent = of_get_dma_parent(np);
+       else
+               np = of_node_get(parent);
        if (!np)
                return -ENODEV;

-       ret = of_dma_get_range(np, &dma_addr, &paddr, &size);
+       ret = of_dma_get_range(parent, &dma_addr, &paddr, &size);
+       of_node_put(parent);
        if (ret < 0) {
                /*
                 * For legacy reasons, we have to assume some devices need

On Thu, 2019-10-03 at 20:53 -0500, Rob Herring wrote:
> > > > But I think that with this series, given the fact that we now treat the

> > > > lack

> > > > of

> > > > dma-ranges as a 1:1 mapping instead of an error, we could rewrite the

> > > > function

> > > > like this:

> > > 

> > > Now, I'm reconsidering allowing this abuse... It's better if the code

> > > which understands the bus structure in DT for a specific bus passes in

> > > the right thing. Maybe I should go back to Robin's version (below).

> > > OTOH, the existing assumption that 'dma-ranges' was in the immediate

> > > parent was an assumption on the bus structure which maybe doesn't

> > > always apply.

> > > 

> > > diff --git a/drivers/of/device.c b/drivers/of/device.c

> > > index a45261e21144..6951450bb8f3 100644

> > > --- a/drivers/of/device.c

> > > +++ b/drivers/of/device.c

> > > @@ -98,12 +98,15 @@ int of_dma_configure(struct device *dev, struct

> > > device_node *parent, bool force_

> > >         u64 mask;

> > > 

> > >         np = dev->of_node;

> > > -       if (!np)

> > > -               np = parent;

> > > +       if (np)

> > > +               parent = of_get_dma_parent(np);

> > > +       else

> > > +               np = of_node_get(parent);

> > >         if (!np)

> > >                 return -ENODEV;

> > > 

> > > -       ret = of_dma_get_range(np, &dma_addr, &paddr, &size);

> > > +       ret = of_dma_get_range(parent, &dma_addr, &paddr, &size);

> > > +       of_node_put(parent);

> > >         if (ret < 0) {

> > >                 /*

> > >                  * For legacy reasons, we have to assume some devices need

> > 

> > I spent some time thinking about your comments and researching. I came to

> > the

> > realization that both these solutions break the usage in

> > drivers/gpu/drm/sun4i/sun4i_backend.c:805. In that specific case both

> > 'dev->of_node' and 'parent' exist yet the device receiving the configuration

> > and 'parent' aren't related in any way.

> 

> I knew there was some reason I didn't like those virtual DT nodes...

> 

> That does seem to be the oddest case. Several of the others are just

> non-DT child platform devices. Perhaps we need a "copy the DMA config

> from another struct device (or parent struct device)" function to

> avoid using a DT function on a non-DT device.

> 

> > IOW we can't just use 'dev->of_node' as a starting point to walk upwards the

> > tree. We always have to respect whatever DT node the bus provided, and start

> > there. This clashes with the current solutions, as they are based on the

> > fact

> > that we can use dev->of_node when present.

> 

> Yes, you are right.

> 

> > My guess at this point, if we're forced to honor that behaviour, is that we

> > have to create a new API for the PCI use case. Something the likes of

> > of_dma_configure_parent().

> 

> I think of_dma_configure just has to work with the device_node of

> either the device or the device parent and dev->of_node is never used

> unless the caller sets it.


Fine, so given the following two distinct uses of
of_dma_configure(struct device *dev, struct device_node *np, bool ...):

- dev->of_node == np: Platform bus' typical use, we imperatively have to start
  parsing dma-ranges from np's DMA parent, as the device we're configuring
  might be a bus containing dma-ranges himself. For example a platform PCIe bus.

- dev->of_node != np: Here the bus is pulling some trick. The device might or
  might not be represented in DT and np might be a bus or a device. But one
  thing I realised is that device being configured never represents a memory
  mapped bus. Assuming this assumption is acceptable, we can traverse the DT
  tree starting from np and get a correct configuration as long as dma-ranges
  not being present is interpreted as a 1:1 mapping.

The resulting code, which I tested on an RPi4, Freescale Layerscape and passes
OF's unit tests, looks like this:

int of_dma_configure(struct device *dev, struct device_node *np, bool force_dma)
{
	u64 dma_addr, paddr, size = 0;
	struct device_node *parent;
	u64 mask;
	int ret;

	if (!np)
		return -ENODEV;

	parent = of_node_get(np);
	if (dev->of_node == parent)
		parent = of_get_next_dma_parent(np);

	ret = of_dma_get_range(parent, &dma_addr, &paddr, &size);
	of_node_put(parent);

	[...]
}

Would that be acceptable?

Regards,
Nicolas