linux-kernel - Re: [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 11:20:23 +0100
From:   Hans de Goede <hdegoede@...hat.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Jani Nikula <jani.nikula@...el.com>,
        intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        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>
Subject: Re: [PATCH v2 6/7] drm/i915/dsi: Replace poking of CHV GPIOs behind
 the driver's back

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.

> Meanwhile I will look into the change you sent (and hopefully we can
> incorporate something in v3 for v4).

Ok, lets go with your v3.

I'll prepare a patch  to move the unregistering of the existing
conflicting GPIO lookup from intel_dsi_vbt_gpio_cleanup()
to the end of intel_dsi_vbt_gpio_init() to avoid the conflict
we have there.

Note you still need the first part of my patch which is
an unrelated bugfix:

--- a/drivers/gpu/drm/i915/display/intel_dsi_vbt.c
+++ b/drivers/gpu/drm/i915/display/intel_dsi_vbt.c
@@ -219,8 +219,7 @@ static void soc_exec_gpio(struct intel_connector *connector, const char *con_id,
 	} else {
 		gpio_desc = devm_gpiod_get_index(dev_priv->drm.dev,
 						 con_id, gpio_index,
-						 value ? GPIOD_OUT_LOW :
-						 GPIOD_OUT_HIGH);
+						 value ? GPIOD_OUT_HIGH : GPIOD_OUT_LOW);
 		if (IS_ERR(gpio_desc)) {
 			drm_err(&dev_priv->drm,
 				"GPIO index %u request failed (%pe)\n",

Regards,

Hans