Re: [PATCH] i2c: tegra: Set ACPI node as primary fwnode

[Jon Hunter]

On 18/11/2022 10:18, Thierry Reding wrote:
> On Fri, Nov 18, 2022 at 09:38:52AM +0000, Jon Hunter wrote:
> > On 17/11/2022 10:04, Akhil R wrote:
> > > Set ACPI node as the primary fwnode of I2C adapter to allow
> > > enumeration of child devices from the ACPI table
> > >
> > > Signed-off-by: Zubair Waheed <zwaheed@xxxxxxxxxx>
> > > Signed-off-by: Akhil R <akhilrajeev@xxxxxxxxxx>
> > > ---
> > >    drivers/i2c/busses/i2c-tegra.c | 1 +
> > >    1 file changed, 1 insertion(+)
> > >
> > > diff --git a/drivers/i2c/busses/i2c-tegra.c b/drivers/i2c/busses/i2c-tegra.c
> > > index 954022c04cc4..69c9ae161bbe 100644
> > > --- a/drivers/i2c/busses/i2c-tegra.c
> > > +++ b/drivers/i2c/busses/i2c-tegra.c
> > > @@ -1826,6 +1826,7 @@ static int tegra_i2c_probe(struct platform_device *pdev)
> > >    	i2c_dev->adapter.class = I2C_CLASS_DEPRECATED;
> > >    	i2c_dev->adapter.algo = &tegra_i2c_algo;
> > >    	i2c_dev->adapter.nr = pdev->id;
> > > +	ACPI_COMPANION_SET(&i2c_dev->adapter.dev, ACPI_COMPANION(&pdev->dev));
> > >    	if (i2c_dev->hw->supports_bus_clear)
> > >    		i2c_dev->adapter.bus_recovery_info = &tegra_i2c_recovery_info;
> >
> >
> > Do we always want to set as the primary fwnode even when booting with
> > device-tree? I some other drivers do, but I also see some others ...
> >
> >   if (has_acpi_companion(dev))
> >          ACPI_COMPANION_SET(&i2c_dev->adapter.dev,
> >                             ACPI_COMPANION(&pdev->dev));
> >
> > It would be nice to know why it is OK to always do this even for device-tree
> > because it is not clear to me.
>
> ACPI_COMPANION() returns NULL if there is no ACPI companion, which will
> cause ACPI_COMPANION_SET() to set the primary fwnode to NULL. If I read
> the code for set_primary_fwnode() correctly, that's essentially a no-op
> for DT devices.

Yes it does, but doesn't it is not clear to me if it is a good idea to 
pass NULL to set_primary_fwnode(). It does seem to handle this but my 
biggest gripe is the lack of explanation in the commit message why this 
is OK.

Jon

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