linux-kernel - Re: [PATCH 15/20] drivers/gpu/drm/i915/display: remove I2C_CLASS

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Message-ID: <105d8b23-e199-4fef-bf28-f66f29b7932f@gmail.com>
Date:   Mon, 13 Nov 2023 19:20:29 +0100
From:   Heiner Kallweit <hkallweit1@...il.com>
To:     Jani Nikula <jani.nikula@...ux.intel.com>,
        Wolfram Sang <wsa@...nel.org>
Cc:     linux-i2c@...r.kernel.org,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 15/20] drivers/gpu/drm/i915/display: remove I2C_CLASS_DDC
 support

On 13.11.2023 18:50, Jani Nikula wrote:
> On Mon, 13 Nov 2023, Heiner Kallweit <hkallweit1@...il.com> wrote:
>> On 13.11.2023 13:17, Jani Nikula wrote:
>>> On Mon, 13 Nov 2023, Heiner Kallweit <hkallweit1@...il.com> wrote:
>>>> After removal of the legacy EEPROM driver and I2C_CLASS_DDC support in
>>>> olpc_dcon there's no i2c client driver left supporting I2C_CLASS_DDC.
>>>> Class-based device auto-detection is a legacy mechanism and shouldn't
>>>> be used in new code. So we can remove this class completely now.
>>>
>>> So this is copy-pasted to all commits and the cover letter, but please
>>> do explain why there are no functional changes here (or are there?),
>>> without me having to go through the i2c stack and try to find the
>>> commits alluded to in "After removal of the legacy ...".
>>>
>> Legacy eeprom driver was marked deprecated 4 yrs ago with:
>> 3079b54aa9a0 ("eeprom: Warn that the driver is deprecated")
>> Now it has been removed with:
>> 0113a99b8a75 ("eeprom: Remove deprecated legacy eeprom driver")
>>
>> Declaration of I2C_CLASS_DDC support is a no-op now, so there's
>> no functional change in this patch.
>>
>> If loaded manually, the legacy eeprom driver exposed the DDC EEPROM
>> to userspace. If this functionality is needed, then now the DDC
>> EEPROM has to be explicitly instantiated using at24.
>>
>> See also:
>> https://docs.kernel.org/i2c/instantiating-devices.html
> 
> I'll take your word for it. Though none of the documentation I can find
> say that setting the class is legacy or deprecated or should be
> avoided. *shrug*.
> 
I have to agree that it's not obvious that class-based instantiation
is considered a legacy mechanism. The commit message of this 9 yrs old
commit provides an explanation.

0c176170089c ("i2c: add deprecation warning for class based instantiation")

> Acked-by: Jani Nikula <jani.nikula@...el.com>
> 
Thanks

> 
>>
>>
>>> What does this mean?
>>>
>>>
>>> BR,
>>> Jani.
>>>
>> Heiner
>>
>>>
>>>>
>>>> Preferably this series should be applied via the i2c tree.
>>>>
>>>> Signed-off-by: Heiner Kallweit <hkallweit1@...il.com>
>>>>
>>>> ---
>>>>  drivers/gpu/drm/i915/display/intel_gmbus.c |    1 -
>>>>  drivers/gpu/drm/i915/display/intel_sdvo.c  |    1 -
>>>>  2 files changed, 2 deletions(-)
>>>>
>>>> diff --git a/drivers/gpu/drm/i915/display/intel_gmbus.c b/drivers/gpu/drm/i915/display/intel_gmbus.c
>>>> index 40d7b6f3f..e9e4dcf34 100644
>>>> --- a/drivers/gpu/drm/i915/display/intel_gmbus.c
>>>> +++ b/drivers/gpu/drm/i915/display/intel_gmbus.c
>>>> @@ -899,7 +899,6 @@ int intel_gmbus_setup(struct drm_i915_private *i915)
>>>>  		}
>>>>  
>>>>  		bus->adapter.owner = THIS_MODULE;
>>>> -		bus->adapter.class = I2C_CLASS_DDC;
>>>>  		snprintf(bus->adapter.name,
>>>>  			 sizeof(bus->adapter.name),
>>>>  			 "i915 gmbus %s", gmbus_pin->name);
>>>> diff --git a/drivers/gpu/drm/i915/display/intel_sdvo.c b/drivers/gpu/drm/i915/display/intel_sdvo.c
>>>> index a636f42ce..5e64d1baf 100644
>>>> --- a/drivers/gpu/drm/i915/display/intel_sdvo.c
>>>> +++ b/drivers/gpu/drm/i915/display/intel_sdvo.c
>>>> @@ -3311,7 +3311,6 @@ intel_sdvo_init_ddc_proxy(struct intel_sdvo_ddc *ddc,
>>>>  	ddc->ddc_bus = ddc_bus;
>>>>  
>>>>  	ddc->ddc.owner = THIS_MODULE;
>>>> -	ddc->ddc.class = I2C_CLASS_DDC;
>>>>  	snprintf(ddc->ddc.name, I2C_NAME_SIZE, "SDVO %c DDC%d",
>>>>  		 port_name(sdvo->base.port), ddc_bus);
>>>>  	ddc->ddc.dev.parent = &pdev->dev;
>>>>
>>>
>>
>