linux-kernel - Re: [Intel-gfx] [PATCH v2 6/7] drm/i915/dsi: Replace poking of CHV GPIOs behind the driver's back

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Date:   Wed, 1 Nov 2023 11:40:35 +0100
From:   Hans de Goede <hdegoede@...hat.com>
To:     Ville Syrjälä <ville.syrjala@...ux.intel.com>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Jani Nikula <jani.nikula@...el.com>,
        intel-gfx@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, Daniel Vetter <daniel@...ll.ch>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        David Airlie <airlied@...il.com>
Subject: Re: [Intel-gfx] [PATCH v2 6/7] drm/i915/dsi: Replace poking of CHV
 GPIOs behind the driver's back

Hi,

On 11/1/23 11:34, Ville Syrjälä wrote:
> On Wed, Nov 01, 2023 at 11:20:23AM +0100, Hans de Goede wrote:
>> Hi,
>>
>> On 11/1/23 10:32, Andy Shevchenko wrote:
>>> On Tue, Oct 31, 2023 at 10:15:52PM +0100, Hans de Goede wrote:
>>>> On 10/31/23 17:07, Hans de Goede wrote:
>>>>> On 10/24/23 18:11, Andy Shevchenko wrote:
>>>>>> On Tue, Oct 24, 2023 at 06:57:38PM +0300, Andy Shevchenko wrote:
>>>
>>> ...
>>>
>>>>> As for the CHT support, I have not added that to my tree yet, I would
>>>>> prefer to directly test the correct/fixed patch.
>>>>
>>>> And I hit the "jackpot" on the first device I tried and the code needed
>>>> some fixing to actually work, so here is something to fold into v3 to
>>>> fix things:
>>>
>>> Thanks!
>>>
>>> But let me first send current v3 as it quite differs to v2 in the sense
>>> of how I do instantiate GPIO lookup tables.
>>
>> The problem is there already is a GPIO lookup table registered for
>> the "0000:00:02.0" device by intel_dsi_vbt_gpio_init() and there can
>> be only be one GPIO lookup table per device. So no matter how you
>> instantiate GPIO lookup tables it will not work.
>>
>> The solution that I chose is to not instantiate a GPIO lookup table
>> at all and instead to extend the existing table with an extra entry.
>>
>> Although thinking more about it I must admit that this is racy.
>>
>> So a better idea would be to unregister the GPIO lookup
>> table registered by intel_dsi_vbt_gpio_init() after getting
>> the GPIOs there, that would allow instantiating a new one
>> from soc_exec_opaque_gpio() as it currently does and that
>> would be race free.
> 
> The proper solution would likely be be to pre-parse the sequences
> to determine which GPIOs are actually needed. That would also get
> rid of the bxt_gpio_table[] eyesore.

Interesting suggestion. Note that intel_dsi_vbt_gpio_init() arm
only runs on byt and cht though, so that is something to keep
in mind.

Regards,

Hans