Re: [PATCH] drm/simpledrm: Drop superfluous primary plane .atomic_check return logic

[Thomas Zimmermann <tzimmermann@suse.de>]

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Hi

Am 05.09.22 um 13:06 schrieb Javier Martinez Canillas:
> Hello Thomas,
> 
> On 9/5/22 12:57, Thomas Zimmermann wrote:
>> Hi Javier
>>
>> Am 31.08.22 um 13:12 schrieb Javier Martinez Canillas:
>>> The simpledrm_primary_plane_helper_atomic_check() function is more complex
>>> than needed. It first checks drm_atomic_helper_check_plane_state() returns
>>> value to decide whether to return this or zero.
>>>
>>> But it could just return that function return value directly. It also does
>>> a check if new_plane_state->visible isn't set, but returns zero regardless.
>>>
>>> Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
>>> ---
>>>
>>>    drivers/gpu/drm/tiny/simpledrm.c | 15 ++++-----------
>>>    1 file changed, 4 insertions(+), 11 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/tiny/simpledrm.c b/drivers/gpu/drm/tiny/simpledrm.c
>>> index a81f91814595..0be47f40247a 100644
>>> --- a/drivers/gpu/drm/tiny/simpledrm.c
>>> +++ b/drivers/gpu/drm/tiny/simpledrm.c
>>> @@ -485,21 +485,14 @@ static int simpledrm_primary_plane_helper_atomic_check(struct drm_plane *plane,
>>>    	struct drm_plane_state *new_plane_state = drm_atomic_get_new_plane_state(new_state, plane);
>>>    	struct drm_crtc *new_crtc = new_plane_state->crtc;
>>>    	struct drm_crtc_state *new_crtc_state = NULL;
>>> -	int ret;
>>>    
>>>    	if (new_crtc)
>>>    		new_crtc_state = drm_atomic_get_new_crtc_state(new_state, new_crtc);
>>>    
>>> -	ret = drm_atomic_helper_check_plane_state(new_plane_state, new_crtc_state,
>>> -						  DRM_PLANE_NO_SCALING,
>>> -						  DRM_PLANE_NO_SCALING,
>>> -						  false, false);
>>> -	if (ret)
>>> -		return ret;
>>> -	else if (!new_plane_state->visible)
>>> -		return 0;
>>> -
>>> -	return 0;
>>> +	return drm_atomic_helper_check_plane_state(new_plane_state, new_crtc_state,
>>> +						   DRM_PLANE_NO_SCALING,
>>> +						   DRM_PLANE_NO_SCALING,
>>> +						   false, false);
>>
>> I'm undecided on this change. I know it's correct and more to the point.
>> But the call's logic is non-intuitive: the call either returns an error
>> or we have to test ->visible afterwards. So I wrote it explicitly.
>>
> 
> Yes, but the check has no effect so I found it even less intuitive. Maybe
> add a comment then if you wan to keep the current code?
>   
>> I saw that your change to ssd130x also uses the pattern. If we find more
>> such drivers, we could implement the atomic check as a helper. I suggest
>> drm_plane_helper_atomic_check_fixed() in drm_plane_helper.c
>>
> 
> Sure. I can add a preparatory change in v2 that adds that helper and then
> use it in the follow-up patch.
> 

Maybe wait for your ssd130x changes to land and then you can convert 
both drivers to the new helper.

Best regards
Thomas


-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev

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