Re:Re: [PATCH] gpu/drm: make crtc check before new_connector circle

[Bernard]

From: Daniel Vetter <daniel@xxxxxxxx>
Date: 2020-11-02 18:17:24
To:  Bernard Zhao <bernard@xxxxxxxx>
Cc:  Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx>,Maxime Ripard <mripard@xxxxxxxxxx>,Thomas Zimmermann <tzimmermann@xxxxxxx>,David Airlie <airlied@xxxxxxxx>,Daniel Vetter <daniel@xxxxxxxx>,dri-devel@xxxxxxxxxxxxxxxxxxxxx,linux-kernel@xxxxxxxxxxxxxxx,opensource.kernel@xxxxxxxx
Subject: Re: [PATCH] gpu/drm: make crtc check before new_connector circle>On Sun, Nov 01, 2020 at 06:58:51PM -0800, Bernard Zhao wrote:
>> In function prepare_signaling, crtc check (c==0) is not related
>> with the next new_connector circle, maybe we can put the crtc
>> check just after the crtc circle and before new_connector circle.
>> This change is to make the code to run a bit first.
>
>I'm a bit confused here with your explanation, I'm not understanding why
>you do this change ... Can you pls elaborate? Maybe give an example or
>something of the problem this patch solves, that often helps.
>
>Thanks, Daniel

Hi:

This change is to make the function return error earlier when run into the error branch:
if (c == 0 && (arg->flags & DRM_MODE_PAGE_FLIP_EVENT))
    return -EINVAL;
There two main FOR circles in this function, and the second FOR circle never changes the if condition("(c == 0 && (arg->flags & DRM_MODE_PAGE_FLIP_EVENT))") variable`s value, like c & arg->flags.
So I think maybe we can check this condition before the second for circle, and return the error earlier when run into this error branch.

BR//Bernard

>> 
>> Signed-off-by: Bernard Zhao <bernard@xxxxxxxx>
>> ---
>>  drivers/gpu/drm/drm_atomic_uapi.c | 13 ++++++-------
>>  1 file changed, 6 insertions(+), 7 deletions(-)
>> 
>> diff --git a/drivers/gpu/drm/drm_atomic_uapi.c b/drivers/gpu/drm/drm_atomic_uapi.c
>> index 25c269bc4681..566110996474 100644
>> --- a/drivers/gpu/drm/drm_atomic_uapi.c
>> +++ b/drivers/gpu/drm/drm_atomic_uapi.c
>> @@ -1182,6 +1182,12 @@ static int prepare_signaling(struct drm_device *dev,
>>  
>>  		c++;
>>  	}
>> +	/*
>> +	 * Having this flag means user mode pends on event which will never
>> +	 * reach due to lack of at least one CRTC for signaling
>> +	 */
>> +	if (c == 0 && (arg->flags & DRM_MODE_PAGE_FLIP_EVENT))
>> +		return -EINVAL;
>>  
>>  	for_each_new_connector_in_state(state, conn, conn_state, i) {
>>  		struct drm_writeback_connector *wb_conn;
>> @@ -1220,13 +1226,6 @@ static int prepare_signaling(struct drm_device *dev,
>>  		conn_state->writeback_job->out_fence = fence;
>>  	}
>>  
>> -	/*
>> -	 * Having this flag means user mode pends on event which will never
>> -	 * reach due to lack of at least one CRTC for signaling
>> -	 */
>> -	if (c == 0 && (arg->flags & DRM_MODE_PAGE_FLIP_EVENT))
>> -		return -EINVAL;
>> -
>>  	return 0;
>>  }
>>  
>> -- 
>> 2.29.0
>> 
>
>-- 
>Daniel Vetter
>Software Engineer, Intel Corporation
>http://blog.ffwll.ch