linux-kernel - Re: [PATCH v3 2/3] drm/exynos: exynos7_drm_decon: fix call of decon

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Message-ID: <c4348867644c2e1d0a4fc47f3291855b@disroot.org>
Date: Fri, 27 Jun 2025 13:39:33 +0000
From: Kaustabh Chakraborty <kauschluss@...root.org>
To: Inki Dae <daeinki@...il.com>
Cc: Seung-Woo Kim <sw0312.kim@...sung.com>, Kyungmin Park
 <kyungmin.park@...sung.com>, David Airlie <airlied@...il.com>, Simona Vetter
 <simona@...ll.ch>, Krzysztof Kozlowski <krzk@...nel.org>, Alim Akhtar
 <alim.akhtar@...sung.com>, Maarten Lankhorst
 <maarten.lankhorst@...ux.intel.com>, Maxime Ripard <mripard@...nel.org>,
 Thomas Zimmermann <tzimmermann@...e.de>, Rob Herring <robh@...nel.org>,
 Conor Dooley <conor@...nel.org>, Ajay Kumar <ajaykumar.rs@...sung.com>,
 Akshu Agrawal <akshua@...il.com>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
 Conor Dooley <conor+dt@...nel.org>, dri-devel@...ts.freedesktop.org,
 linux-arm-kernel@...ts.infradead.org, linux-samsung-soc@...r.kernel.org,
 linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
 stable@...r.kernel.org
Subject: Re: [PATCH v3 2/3] drm/exynos: exynos7_drm_decon: fix call of
 decon_commit()

On 2025-06-27 04:06, Inki Dae wrote:
> Hi,
> 
> 2025년 6월 27일 (금) 오전 4:21, Kaustabh Chakraborty 
> <kauschluss@...root.org>님이 작성:
>> 
>> decon_commit() has a condition guard at the beginning:
>> 
>>         if (ctx->suspended)
>>                 return;
>> 
>> But, when it is being called from decon_atomic_enable(), 
>> ctx->suspended
>> is still set to true, which prevents its execution. decon_commit() is
>> vital for setting up display timing values, without which the display
>> pipeline fails to function properly. Call the function after
>> ctx->suspended is set to false as a fix.
> 
> Good observation. However, I think a more generic solution is needed.
> 
>> 
>> Cc: stable@...r.kernel.org
>> Fixes: 96976c3d9aff ("drm/exynos: Add DECON driver")
>> Signed-off-by: Kaustabh Chakraborty <kauschluss@...root.org>
>> ---
>>  drivers/gpu/drm/exynos/exynos7_drm_decon.c | 4 ++--
>>  1 file changed, 2 insertions(+), 2 deletions(-)
>> 
>> diff --git a/drivers/gpu/drm/exynos/exynos7_drm_decon.c 
>> b/drivers/gpu/drm/exynos/exynos7_drm_decon.c
>> index 
>> f91daefa9d2bc5e314c279822047e60ee0d7ca99..43bcbe2e2917df43d7c2d27a9771e892628dd682 
>> 100644
>> --- a/drivers/gpu/drm/exynos/exynos7_drm_decon.c
>> +++ b/drivers/gpu/drm/exynos/exynos7_drm_decon.c
>> @@ -583,9 +583,9 @@ static void decon_atomic_enable(struct 
>> exynos_drm_crtc *crtc)
>>         if (test_and_clear_bit(0, &ctx->irq_flags))
>>                 decon_enable_vblank(ctx->crtc);
>> 
>> -       decon_commit(ctx->crtc);
>> -
>>         ctx->suspended = false;
>> +
>> +       decon_commit(ctx->crtc);
> 
> There seem to be three possible solutions:
> 
> 1. Remove all code related to ctx->suspended. If the pipeline flow is
> properly managed as in the exynos5433_drm_decon.c module, checking the
> ctx->suspended state may no longer be necessary.
> 2. Remove the ctx->suspended check from decon_commit(). Since the
> runtime PM resume is already called before decon_commit() in
> decon_atomic_enable(), the DECON controller should already be enabled
> at the hardware level, and decon_commit() should work correctly.
> 3. Move the code that updates ctx->suspended from
> decon_atomic_enable() and decon_atomic_disable() to
> exynos7_decon_resume() and exynos7_decon_suspend(), respectively. The
> decon_atomic_enable() function calls pm_runtime_resume_and_get(),
> which ultimately triggers exynos7_decon_resume(). It would be more
> appropriate to set ctx->suspended = false in the
> exynos7_decon_resume() function, as this is the standard place to
> handle hardware state changes and resume actions.
> decon_atomic_enable() is responsible for requesting enablement of the
> DECON controller, but actual hardware state transitions will be
> handled within exynos7_decon_resume() and exynos7_decon_suspend().
> 
> 
> Unfortunately, I do not have hardware to test this patch myself. Would
> it be possible for you to try one of these approaches and verify the
> behavior?
> Option 1 would be the best solution if feasible.

Yes, it works fine indeed. Thanks!

> 
> Thanks,
> Inki Dae
> 
>>  }
>> 
>>  static void decon_atomic_disable(struct exynos_drm_crtc *crtc)
>> 
>> --
>> 2.49.0
>> 
>>