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: <c257c80e-c449-4750-b822-94f1d1bd8a57@linux.dev>
Date: Tue, 14 Jan 2025 22:22:51 +0530
From: Aradhya Bhatia <aradhya.bhatia@...ux.dev>
To: Maxime Ripard <mripard@...nel.org>
Cc: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>,
 Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
 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>,
 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 22:13, Maxime Ripard wrote:
> On Tue, Jan 14, 2025 at 10:05:56PM +0530, Aradhya Bhatia wrote:
>>
>>
>> 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.
> 
> Whatever you do, I think that we're at a point where the bridge chain
> traversal is complicated enough that we'll want to have tests for all
> cases.
>

I don't think I follow. Which all cases are you referring to?


Regards
Aradhya