linux-kernel - Re: [PATCH 1/2] drm/virtio: fix unblank

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Message-ID: <20200901102006.GZ2352366@phenom.ffwll.local>
Date:   Tue, 1 Sep 2020 12:20:06 +0200
From:   Daniel Vetter <daniel@...ll.ch>
To:     Gerd Hoffmann <kraxel@...hat.com>
Cc:     dri-devel@...ts.freedesktop.org, Daniel Vetter <daniel@...ll.ch>,
        1882851@...s.launchpad.net, David Airlie <airlied@...ux.ie>,
        Chia-I Wu <olvaffe@...il.com>,
        "open list:VIRTIO GPU DRIVER" 
        <virtualization@...ts.linux-foundation.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] drm/virtio: fix unblank

On Tue, Aug 18, 2020 at 09:25:10AM +0200, Gerd Hoffmann wrote:
> When going through a disable/enable cycle without changing the
> framebuffer the optimization added by commit 3954ff10e06e ("drm/virtio:
> skip set_scanout if framebuffer didn't change") causes the screen stay
> blank.  Add a bool to force an update to fix that.
> 
> v2: use drm_atomic_crtc_needs_modeset() (Daniel).
> 
> Cc: 1882851@...s.launchpad.net
> Fixes: 3954ff10e06e ("drm/virtio: skip set_scanout if framebuffer didn't change")
> Signed-off-by: Gerd Hoffmann <kraxel@...hat.com>
> ---
>  drivers/gpu/drm/virtio/virtgpu_drv.h     |  1 +
>  drivers/gpu/drm/virtio/virtgpu_display.c | 11 +++++++++++
>  drivers/gpu/drm/virtio/virtgpu_plane.c   |  4 +++-
>  3 files changed, 15 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/virtio/virtgpu_drv.h b/drivers/gpu/drm/virtio/virtgpu_drv.h
> index 9ff9f4ac0522..4ab1b0ba2925 100644
> --- a/drivers/gpu/drm/virtio/virtgpu_drv.h
> +++ b/drivers/gpu/drm/virtio/virtgpu_drv.h
> @@ -138,6 +138,7 @@ struct virtio_gpu_output {
>  	int cur_x;
>  	int cur_y;
>  	bool enabled;
> +	bool needs_modeset;

Maybe for a follow-up in -next: The clean atomic way of doing this is to
put this into a virtio_crtc_state, compute it in atomic_check, and then
fish it out (through old_state->state lookup, somewhat contrived I know)
in the commit side. Putting random atomic commit state tracking stuff into
non-state structures without appropriate amounts of locks is kinda iffy
and means more work for reviewers pondering whether it all works
correctly.

Cheers, Daniel


>  };
>  #define drm_crtc_to_virtio_gpu_output(x) \
>  	container_of(x, struct virtio_gpu_output, crtc)
> diff --git a/drivers/gpu/drm/virtio/virtgpu_display.c b/drivers/gpu/drm/virtio/virtgpu_display.c
> index 2c2742b8d657..6c26b41f4e0d 100644
> --- a/drivers/gpu/drm/virtio/virtgpu_display.c
> +++ b/drivers/gpu/drm/virtio/virtgpu_display.c
> @@ -123,6 +123,17 @@ static int virtio_gpu_crtc_atomic_check(struct drm_crtc *crtc,
>  static void virtio_gpu_crtc_atomic_flush(struct drm_crtc *crtc,
>  					 struct drm_crtc_state *old_state)
>  {
> +	struct virtio_gpu_output *output = drm_crtc_to_virtio_gpu_output(crtc);
> +
> +	/*
> +	 * virtio-gpu can't do modeset and plane update operations
> +	 * independant from each other.  So the actual modeset happens
> +	 * in the plane update callback, and here we just check
> +	 * whenever we must force the modeset.
> +	 */
> +	if (drm_atomic_crtc_needs_modeset(crtc->state)) {
> +		output->needs_modeset = true;
> +	}
>  }
>  
>  static const struct drm_crtc_helper_funcs virtio_gpu_crtc_helper_funcs = {
> diff --git a/drivers/gpu/drm/virtio/virtgpu_plane.c b/drivers/gpu/drm/virtio/virtgpu_plane.c
> index 52d24179bcec..65757409d9ed 100644
> --- a/drivers/gpu/drm/virtio/virtgpu_plane.c
> +++ b/drivers/gpu/drm/virtio/virtgpu_plane.c
> @@ -163,7 +163,9 @@ static void virtio_gpu_primary_plane_update(struct drm_plane *plane,
>  	    plane->state->src_w != old_state->src_w ||
>  	    plane->state->src_h != old_state->src_h ||
>  	    plane->state->src_x != old_state->src_x ||
> -	    plane->state->src_y != old_state->src_y) {
> +	    plane->state->src_y != old_state->src_y ||
> +	    output->needs_modeset) {
> +		output->needs_modeset = false;
>  		DRM_DEBUG("handle 0x%x, crtc %dx%d+%d+%d, src %dx%d+%d+%d\n",
>  			  bo->hw_res_handle,
>  			  plane->state->crtc_w, plane->state->crtc_h,
> -- 
> 2.18.4
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch