Message-ID: <392a239a-14da-c544-a1f9-09d8b25d3e07@gmail.com>
Date:   Fri, 3 Dec 2021 16:58:11 +0100
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To:     Mark Yacoub <markyacoub@chromium.org>,
        dri-devel@lists.freedesktop.org
Cc:     seanpaul@chromium.org, chunkuang.hu@kernel.org,
        p.zabel@pengutronix.de, jason-jh.lin@mediatek.com,
        tzungbi@google.com, Mark Yacoub <markyacoub@google.com>,
        Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
        Maxime Ripard <mripard@kernel.org>,
        Thomas Zimmermann <tzimmermann@suse.de>,
        David Airlie <airlied@linux.ie>,
        Daniel Vetter <daniel@ffwll.ch>, linux-kernel@vger.kernel.org
References: <20211202151200.3125685-1-markyacoub@chromium.org>
From:   Matthias Brugger <matthias.bgg@gmail.com>
Subject: Re: [PATCH] drm: send vblank event with the attached sequence rather
 than current
In-Reply-To: <20211202151200.3125685-1-markyacoub@chromium.org>
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Hi Mark,

On 02/12/2021 16:11, Mark Yacoub wrote:
> From: Mark Yacoub <markyacoub@google.com>
> 

please make sure to add the linux-mediatek mailinglist in any follow-up 
communication.

Regards,
Matthias

> [Why]
> drm_handle_vblank_events loops over vblank_event_list to send any event
> that is current or has passed.
> More than 1 event could be pending with past sequence time that need to
> be send. This can be a side effect of drivers without hardware vblank
> counter and they depend on the difference in the timestamps and the
> frame/field duration calculated in drm_update_vblank_count. This can
> lead to 1 vblirq being ignored due to very small diff, resulting in a
> subsequent vblank with 2 pending vblank events to be sent, each with a
> unique sequence expected by user space.
> 
> [How]
> Send each pending vblank event with the sequence it's waiting on instead
> of assigning the current sequence to all of them.
> 
> Fixes igt@kms_flip "Unexpected frame sequence"
> Tested on Jacuzzi (MT8183)
> 
> Signed-off-by: Mark Yacoub <markyacoub@chromium.org>
> ---
>   drivers/gpu/drm/drm_vblank.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c
> index 3417e1ac79185..47da8056abc14 100644
> --- a/drivers/gpu/drm/drm_vblank.c
> +++ b/drivers/gpu/drm/drm_vblank.c
> @@ -1902,7 +1902,7 @@ static void drm_handle_vblank_events(struct drm_device *dev, unsigned int pipe)
>   
>   		list_del(&e->base.link);
>   		drm_vblank_put(dev, pipe);
> -		send_vblank_event(dev, e, seq, now);
> +		send_vblank_event(dev, e, e->sequence, now);
>   	}
>   
>   	if (crtc && crtc->funcs->get_vblank_timestamp)
>