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

[Jon Hunter]

On 18/11/2022 14:27, Akhil R wrote:
> > 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.
> I saw ACPI_COMPANION_SET() as an empty function if CONFIG_ACPI is not set.

That's not the issue. By default CONFIG_ACPI is enabled for arm64 but 
for Tegra we typically boot with device-tree. So I was more concerned 
about the case where ACPI_COMPANION_SET() is not an empty function.

> Yes, I agree that I should have mentioned this in the commit message.
> Shall I send a v2 with the details added in the commit description?

No need, especially as Thierry has already applied. I am not familiar 
with this function and primary/secondary fwnodes so wanted to understand 
there is no issue for device tree.

Jon

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