linux-kernel - Re: [PATCH] drm/amd/display: fix the ability to use lower resolution modes on eDP

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Date:   Thu, 14 Sep 2023 17:04:18 -0400
From:   Hamza Mahfooz <hamza.mahfooz@....com>
To:     Harry Wentland <harry.wentland@....com>,
        amd-gfx@...ts.freedesktop.org
Cc:     stable@...r.kernel.org, Leo Li <sunpeng.li@....com>,
        Rodrigo Siqueira <Rodrigo.Siqueira@....com>,
        Alex Deucher <alexander.deucher@....com>,
        Christian König <christian.koenig@....com>,
        "Pan, Xinhui" <Xinhui.Pan@....com>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Qingqing Zhuo <Qingqing.Zhuo@....com>,
        Aurabindo Pillai <aurabindo.pillai@....com>,
        Hersen Wu <hersenxs.wu@....com>,
        Srinivasan Shanmugam <srinivasan.shanmugam@....com>,
        Stylon Wang <stylon.wang@....com>,
        Wayne Lin <wayne.lin@....com>, Alan Liu <haoping.liu@....com>,
        Joshua Ashton <joshua@...ggi.es>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/amd/display: fix the ability to use lower resolution
 modes on eDP


On 9/14/23 16:40, Harry Wentland wrote:
> On 2023-09-14 13:53, Hamza Mahfooz wrote:
>> On eDP we can receive invalid modes from dm_update_crtc_state() for
>> entirely new streams for which drm_mode_set_crtcinfo() shouldn't be
>> called on. So, instead of calling drm_mode_set_crtcinfo() from within
>> create_stream_for_sink() we can instead call it from
>> amdgpu_dm_connector_mode_valid(). Since, we are guaranteed to only call
>> drm_mode_set_crtcinfo() for valid modes from that function (invalid
>> modes are rejected by that callback) and that is the only user
>> of create_validate_stream_for_sink() that we need to call
>> drm_mode_set_crtcinfo() for (as before commit cb841d27b876
>> ("drm/amd/display: Always pass connector_state to stream validation"),
>> that is the only place where create_validate_stream_for_sink()'s
>> dm_state was NULL).
>>
> 
> I don't seem to see how a NULL dm_state in
> create_validate_stream_for_sink() (or create_stream_for_sink() for that
> matter) has an impact on the drm_mode_set_crtcinfo() call. That one depends
> on !old_stream and &mode.

If we look back to commit 4a2df0d1f28e ("drm/amd/display: Fixed
non-native modes not lighting up") it seems like the intent was to only
have drm_mode_set_crtcinfo() called for
amdgpu_dm_connector_mode_valid(). Since, even if we go that far back
create_stream_for_sink()'s dm_state was only NULL when it was called
from amdgpu_dm_connector_mode_valid().

> 
> It does look like &mode is an empty mode if we can't find a preferred_mode,
> though. Not sure if that can cause an issue.

I don't think it should be an issue, since before commit 4a2df0d1f28e
("drm/amd/display: Fixed non-native modes not lighting up") we always
called drm_mode_set_crtcinfo() in the aforementioned case (and only for 
that case).

> 
> Harry
> 
>> Cc: stable@...r.kernel.org
>> Link: https://gitlab.freedesktop.org/drm/amd/-/issues/2693
>> Fixes: cb841d27b876 ("drm/amd/display: Always pass connector_state to stream validation")
>> Signed-off-by: Hamza Mahfooz <hamza.mahfooz@....com>
>> ---
>>   drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 4 ++--
>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
>> index 933c9b5d5252..beef4fef7338 100644
>> --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
>> +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
>> @@ -6128,8 +6128,6 @@ create_stream_for_sink(struct amdgpu_dm_connector *aconnector,
>>   
>>   	if (recalculate_timing)
>>   		drm_mode_set_crtcinfo(&saved_mode, 0);
>> -	else if (!old_stream)
>> -		drm_mode_set_crtcinfo(&mode, 0);
>>   
>>   	/*
>>   	 * If scaling is enabled and refresh rate didn't change
>> @@ -6691,6 +6689,8 @@ enum drm_mode_status amdgpu_dm_connector_mode_valid(struct drm_connector *connec
>>   		goto fail;
>>   	}
>>   
>> +	drm_mode_set_crtcinfo(mode, 0);
>> +
>>   	stream = create_validate_stream_for_sink(aconnector, mode,
>>   						 to_dm_connector_state(connector->state),
>>   						 NULL);
> 
-- 
Hamza