linux-kernel - Re: [PATCH 3/4] iio: light: max44009: add missing OF device matching

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Message-ID: <c9cfb54e-1418-ac98-9021-0c27a8bc3c20@linaro.org>
Date:   Sun, 12 Mar 2023 11:15:01 +0100
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Jonathan Cameron <jic23@...nel.org>
Cc:     Marek Vasut <marek.vasut@...il.com>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Michael Hennerich <Michael.Hennerich@...log.com>,
        Robert Eshleman <bobbyeshleman@...il.com>,
        linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/4] iio: light: max44009: add missing OF device matching

On 11/03/2023 19:35, Jonathan Cameron wrote:
> On Sat, 11 Mar 2023 13:28:17 +0100
> Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org> wrote:
> 
>> On 11/03/2023 13:26, Jonathan Cameron wrote:
>>> On Sat, 11 Mar 2023 12:14:56 +0100
>>> Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org> wrote:
>>>   
>>>> The driver currently matches only via i2c_device_id, but also has
>>>> of_device_id table:
>>>>
>>>>   drivers/iio/light/max44009.c:545:34: error: ‘max44009_of_match’ defined but not used [-Werror=unused-const-variable=]
>>>>
>>>> Fixes: 6aef699a7d7e ("iio: light: add driver for MAX44009")
>>>> Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>  
>>>
>>> Don't use of_match_ptr() unless you are absolutely sure no other firmware
>>> route will make use of the of_match_table.
>>>
>>> In this particular case ACPI using PRP0001 is broken by that macro.  
>>
>> It's not broken because there was no matching via PRP0001 due to missing
>> table.
>>
>>>
>>> So good to set the of_match_table, but make sure to always set it
>>> and hence you don't need the __maybe_unused.  
>>
>> So you want to add PRP0001? We can, the fix is for different issue, though.
> 
> There is nothing to add.  You need to do less than you have done in this patch.
> Drop the of_match_ptr() and the __maybe_unused and PRP0001 based matching will just
> work. The PRP0001 path just uses the of_device_id table and needs no

Sure, but that's *adding a feature*. You said that "ACPI using PRP0001
is broken", but it was never here in the first place. PRP0001 *was*
already broken here, not *is*. The patch does not decrease the
functionality.

> specific support in a driver - it doesn't need an ACPI id table or anything like
> that.
> 
> It's a long story, but hindsight says that of_match_ptr() should never have
> existed as it only serves to stop things working that otherwise work for free.

Sure, I can go with ID table always present.

Best regards,
Krzysztof