linux-kernel - Re: [PATCH v7 11/12] drm/atomic-helper: Re-order bridge chain pre-enable and post-disable

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Message-ID: <4518320e-4699-4026-adbe-b28514bde544@ideasonboard.com>
Date: Tue, 14 Jan 2025 15:04:12 +0200
From: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
To: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
 Aradhya Bhatia <aradhya.bhatia@...ux.dev>
Cc: Laurent Pinchart <laurent.pinchart@...asonboard.com>,
 Andrzej Hajda <andrzej.hajda@...el.com>,
 Neil Armstrong <neil.armstrong@...aro.org>, Robert Foss <rfoss@...nel.org>,
 Jonas Karlman <jonas@...boo.se>, Jernej Skrabec <jernej.skrabec@...il.com>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>,
 David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
 Nishanth Menon <nm@...com>, Vignesh Raghavendra <vigneshr@...com>,
 Devarsh Thakkar <devarsht@...com>, Praneeth Bajjuri <praneeth@...com>,
 Udit Kumar <u-kumar1@...com>, Jayesh Choudhary <j-choudhary@...com>,
 DRI Development List <dri-devel@...ts.freedesktop.org>,
 Linux Kernel List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v7 11/12] drm/atomic-helper: Re-order bridge chain
 pre-enable and post-disable

Hi,

On 14/01/2025 13:24, Dmitry Baryshkov wrote:
> On Tue, Jan 14, 2025 at 11:26:25AM +0530, Aradhya Bhatia wrote:
>> Move the bridge pre_enable call before crtc enable, and the bridge
>> post_disable call after the crtc disable.
>>
>> The sequence of enable after this patch will look like:
>>
>> 	bridge[n]_pre_enable
>> 	...
>> 	bridge[1]_pre_enable
>>
>> 	crtc_enable
>> 	encoder_enable
>>
>> 	bridge[1]_enable
>> 	...
>> 	bridge[n]_enable
>>
>> And, the disable sequence for the display pipeline will look like:
>>
>> 	bridge[n]_disable
>> 	...
>> 	bridge[1]_disable
>>
>> 	encoder_disable
>> 	crtc_disable
>>
>> 	bridge[1]_post_disable
>> 	...
>> 	bridge[n]_post_disable
>>
>> The definition of bridge pre_enable hook says that,
>> "The display pipe (i.e. clocks and timing signals) feeding this bridge
>> will not yet be running when this callback is called".
>>
>> Since CRTC is also a source feeding the bridge, it should not be enabled
>> before the bridges in the pipeline are pre_enabled. Fix that by
>> re-ordering the sequence of bridge pre_enable and bridge post_disable.
> 
> The patch contains both refactoring of the corresponding functions and
> changing of the order. Please split it into two separate commits.
> 
>>
>> Signed-off-by: Aradhya Bhatia <a-bhatia1@...com>
>> Signed-off-by: Aradhya Bhatia <aradhya.bhatia@...ux.dev>
>> ---
>>   drivers/gpu/drm/drm_atomic_helper.c | 300 +++++++++++++++++-----------
>>   1 file changed, 181 insertions(+), 119 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
>> index 5186d2114a50..ad6290a4a528 100644
>> --- a/drivers/gpu/drm/drm_atomic_helper.c
>> +++ b/drivers/gpu/drm/drm_atomic_helper.c
>> @@ -74,6 +74,12 @@
>>    * also shares the &struct drm_plane_helper_funcs function table with the plane
>>    * helpers.
>>    */
>> +
>> +enum bridge_chain_operation_type {
>> +	DRM_BRIDGE_PRE_ENABLE_OR_POST_DISABLE,
>> +	DRM_BRIDGE_ENABLE_OR_DISABLE,
>> +};
>> +
> 
> I have mixed feelings towards this approach. I doubt that it actually
> helps. Would you mind replacing it with just 'bool pre_enable' / 'bool
> post_disable' arguments?

If my memory serves, I suggested the enum. I don't like it too much 
either. But neither do I like the boolean that much, as this is not a 
yes/no, on/off case... Then again, maybe boolean is fine here, as the 
"off" case is the "normal/default" case so it's still ok-ish.

But this doesn't matter much, I think. It's internal, and can be 
trivially adjusted later.

  Tomi