[PATCH v2] i2c: of: Try to find an I2C adapter matching the parent

[Thierry Reding]

On Sat, Jan 26, 2019 at 01:37:34PM +0100, Tristan Bastian wrote:
> Am 25.01.19 um 14:11 schrieb Thierry Reding:
> > From: Thierry Reding <treding at nvidia.com>
> > 
> > If an I2C adapter doesn't match the provided device tree node, also try
> > matching the parent's device tree node. This allows finding an adapter
> > based on the device node of the parent device that was used to register
> > it.
> > 
> > This fixes a regression on Tegra124-based Chromebooks (Nyan) where the
> > eDP controller registers an I2C adapter that is used to read to EDID.
> > After commit 993a815dcbb2 ("dt-bindings: panel: Add missing .txt
> > suffix") this stopped working because the I2C adapter could no longer
> > be found. The approach in this patch fixes the regression without
> > introducing the issues that the above commit solved.
> > 
> > Fixes: 17ab7806de0c ("drm: don't link DP aux i2c adapter to the hardware device node")
> > Signed-off-by: Thierry Reding <treding at nvidia.com>
> > ---
> > Changes in v2:
> > - check for both device and parent device tree nodes for each device
> >    instead of looping through the list of devices twice
> > 
> >   drivers/i2c/i2c-core-of.c | 14 +++++++++++++-
> >   1 file changed, 13 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/i2c/i2c-core-of.c b/drivers/i2c/i2c-core-of.c
> > index 6cb7ad608bcd..0f01cdba9d2c 100644
> > --- a/drivers/i2c/i2c-core-of.c
> > +++ b/drivers/i2c/i2c-core-of.c
> > @@ -121,6 +121,17 @@ static int of_dev_node_match(struct device *dev, void *data)
> >   	return dev->of_node == data;
> >   }
> > +static int of_dev_or_parent_node_match(struct device *dev, void *data)
> > +{
> > +	if (dev->of_node == data)
> > +		return 1;
> > +
> > +	if (dev->parent)
> > +		return dev->parent->of_node == data;
> > +
> > +	return 0;
> > +}
> > +
> >   /* must call put_device() when done with returned i2c_client device */
> >   struct i2c_client *of_find_i2c_device_by_node(struct device_node *node)
> >   {
> > @@ -145,7 +156,8 @@ struct i2c_adapter *of_find_i2c_adapter_by_node(struct device_node *node)
> >   	struct device *dev;
> >   	struct i2c_adapter *adapter;
> > -	dev = bus_find_device(&i2c_bus_type, NULL, node, of_dev_node_match);
> > +	dev = bus_find_device(&i2c_bus_type, NULL, node,
> > +			      of_dev_or_parent_node_match);
> >   	if (!dev)
> >   		return NULL;
> 
> I've tested this and can confirm that this fixes the issue on the nyan-big
> chromebook.

Excellent, thanks for testing! Typically if you've tested a patch and
verified that it fixes the problem that you were seeing, it's good to
send this on a line by itself along with your reply:

Tested-by: Tristan Bastian <tristan-c.bastian at gmx.de>

Patchwork will pick this up and it will become part of the commit
message when the patch is applied. This gives you the credit you deserve
for going through the trouble of testing the change.

> Is this fix going to be applied to the LTS kernels too?

The "Fixes:" line in the commit message should ensure that this does get
backported to relevant stable kernels.

Thierry
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