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: <4d2bf1a9-37d8-4f9e-b855-b372179258f2@linux.dev>
Date: Tue, 14 Jan 2025 22:05:56 +0530
From: Aradhya Bhatia <aradhya.bhatia@...ux.dev>
To: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>,
 Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
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



On 1/14/25 18:34, Tomi Valkeinen wrote:
> 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.
> 

Alright! I will drop the enum reference entirely, and just use the
booleans.

Regards
Aradhya