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

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Message-ID: <Y3dcDCgC42QcMX3k@orome>
Date:   Fri, 18 Nov 2022 11:18:52 +0100
From:   Thierry Reding <thierry.reding@...il.com>
To:     Jon Hunter <jonathanh@...dia.com>
Cc:     Akhil R <akhilrajeev@...dia.com>, christian.koenig@....com,
        digetx@...il.com, ldewangan@...dia.com, linux-i2c@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-tegra@...r.kernel.org,
        sumit.semwal@...aro.org, wsa@...nel.org,
        Zubair Waheed <zwaheed@...dia.com>
Subject: Re: [PATCH] i2c: tegra: Set ACPI node as primary fwnode

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@...dia.com>
> > Signed-off-by: Akhil R <akhilrajeev@...dia.com>
> > ---
> >   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.

I guess that the extra check might save a few cycles by not having to
run through all the various conditionals, but it seems a rather minor
saving.

Either way is fine with me, though.

Thierry

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