Re: [PATCH] drm/atomic: Handling the case when setting old crtc for plane

[Daniel Vetter]

On Thu, May 03, 2018 at 11:19:32AM +0530, Satendra Singh Thakur wrote:
> In the func drm_atomic_set_crtc_for_plane, with the current code,
> if crtc of the plane_state and crtc passed as argument to the func
> are same, entire func will executed in vein.
> It will get state of crtc and clear and set the bits in plane_mask.
> All these steps are not required for same old crtc.
> Ideally, we should do nothing in this case, this patch handles the same,
> and causes the program to return without doing anything in such scenario.
> 
> Signed-off-by: Satendra Singh Thakur <satendra.t@xxxxxxxxxxx>
> Cc: Madhur Verma <madhur.verma@xxxxxxxxxxx>
> Cc: Hemanshu Srivastava <hemanshu.s@xxxxxxxxxxx>
> ---
>  drivers/gpu/drm/drm_atomic.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
> index 7d25c42..5bd3365 100644
> --- a/drivers/gpu/drm/drm_atomic.c
> +++ b/drivers/gpu/drm/drm_atomic.c
> @@ -1421,7 +1421,9 @@ drm_atomic_set_crtc_for_plane(struct drm_plane_state *plane_state,
>  {
>  	struct drm_plane *plane = plane_state->plane;
>  	struct drm_crtc_state *crtc_state;
> -
> +	/* Nothing to do for same crtc*/
> +	if (plane_state->crtc == crtc)
> +		return 0;

I didn't do this (both here and in the set_crtc_for_connector functions)
because the overhead is probably way down in the noise compared to the
overall atomic commit machinery. Do you really see this as a hotpath?
-Daniel

>  	if (plane_state->crtc) {
>  		crtc_state = drm_atomic_get_crtc_state(plane_state->state,
>  						       plane_state->crtc);
> -- 
> 2.7.4
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch