linux-kernel - Re: [PATCH] drm/vkms: Solve bug on kms_crc

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Message-ID: <20190228101107.GL2665@phenom.ffwll.local>
Date:   Thu, 28 Feb 2019 11:11:07 +0100
From:   Daniel Vetter <daniel@...ll.ch>
To:     Shayenne Moura <shayenneluzmoura@...il.com>
Cc:     Rodrigo Siqueira <rodrigosiqueiramelo@...il.com>,
        Haneen Mohammed <hamohammed.sa@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/vkms: Solve bug on kms_crc_cursor tests

On Mon, Feb 25, 2019 at 11:26:06AM -0300, Shayenne Moura wrote:
> vkms_crc_work_handle needs the value of the actual frame to
> schedule the workqueue that calls periodically the vblank
> handler and the destroy state functions. However, the frame
> value returned from vkms_vblank_simulate is updated and
> diminished in vblank_get_timestamp because it is not in a
> vblank interrupt, and return an inaccurate value.
> 
> Solve this getting the actual vblank frame directly from the
> vblank->count inside the `struct drm_crtc`, instead of using
> the `drm_accurate_vblank_count` function.
> 
> Signed-off-by: Shayenne Moura <shayenneluzmoura@...il.com>

Sorry for the delay, I'm a bit swamped right now :-/

Debug work you're doing here is really impressive! But I have no idea
what's going on. It doesn't look like it's just papering over a bug (like
the in_vblank_irq check we've discussed on irc), but I also have no idea
why it works.

I'll pull in Ville, he understands this better than me.
-Daniel

> ---
>  drivers/gpu/drm/vkms/vkms_crc.c  | 4 +++-
>  drivers/gpu/drm/vkms/vkms_crtc.c | 4 +++-
>  2 files changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/vkms/vkms_crc.c b/drivers/gpu/drm/vkms/vkms_crc.c
> index d7b409a3c0f8..09a8b00ef1f1 100644
> --- a/drivers/gpu/drm/vkms/vkms_crc.c
> +++ b/drivers/gpu/drm/vkms/vkms_crc.c
> @@ -161,6 +161,8 @@ void vkms_crc_work_handle(struct work_struct *work)
>  	struct vkms_output *out = drm_crtc_to_vkms_output(crtc);
>  	struct vkms_device *vdev = container_of(out, struct vkms_device,
>  						output);
> +	unsigned int pipe = drm_crtc_index(crtc);
> +	struct drm_vblank_crtc *vblank = &crtc->dev->vblank[pipe];
>  	struct vkms_crc_data *primary_crc = NULL;
>  	struct vkms_crc_data *cursor_crc = NULL;
>  	struct drm_plane *plane;
> @@ -196,7 +198,7 @@ void vkms_crc_work_handle(struct work_struct *work)
>  	if (primary_crc)
>  		crc32 = _vkms_get_crc(primary_crc, cursor_crc);
>  
> -	frame_end = drm_crtc_accurate_vblank_count(crtc);
> +	frame_end = vblank->count;
>  
>  	/* queue_work can fail to schedule crc_work; add crc for
>  	 * missing frames
> diff --git a/drivers/gpu/drm/vkms/vkms_crtc.c b/drivers/gpu/drm/vkms/vkms_crtc.c
> index 8a9aeb0a9ea8..9bf3268e2e92 100644
> --- a/drivers/gpu/drm/vkms/vkms_crtc.c
> +++ b/drivers/gpu/drm/vkms/vkms_crtc.c
> @@ -10,6 +10,8 @@ static enum hrtimer_restart vkms_vblank_simulate(struct hrtimer *timer)
>  						  vblank_hrtimer);
>  	struct drm_crtc *crtc = &output->crtc;
>  	struct vkms_crtc_state *state = to_vkms_crtc_state(crtc->state);
> +	unsigned int pipe = drm_crtc_index(crtc);
> +	struct drm_vblank_crtc *vblank = &crtc->dev->vblank[pipe];
>  	u64 ret_overrun;
>  	bool ret;
>  
> @@ -20,7 +22,7 @@ static enum hrtimer_restart vkms_vblank_simulate(struct hrtimer *timer)
>  		DRM_ERROR("vkms failure on handling vblank");
>  
>  	if (state && output->crc_enabled) {
> -		u64 frame = drm_crtc_accurate_vblank_count(crtc);
> +		u64 frame = vblank->count;
>  
>  		/* update frame_start only if a queued vkms_crc_work_handle()
>  		 * has read the data
> -- 
> 2.17.1
> 

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