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

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Date:   Fri, 18 Nov 2022 11:06:49 +0000
From:   Jon Hunter <jonathanh@...dia.com>
To:     Thierry Reding <thierry.reding@...il.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 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@...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.

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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