linux-kernel - Re: [PATCH 30/39] drm: renesas: shmobile: Wait for page flip when turning CRTC off

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Message-ID: <20230623170808.GH2112@pendragon.ideasonboard.com>
Date:   Fri, 23 Jun 2023 20:08:08 +0300
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Geert Uytterhoeven <geert+renesas@...der.be>
Cc:     Kieran Bingham <kieran.bingham+renesas@...asonboard.com>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Magnus Damm <magnus.damm@...il.com>,
        dri-devel@...ts.freedesktop.org, linux-renesas-soc@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 30/39] drm: renesas: shmobile: Wait for page flip when
 turning CRTC off

Hi Geert,

Thank you for the patch.

On Thu, Jun 22, 2023 at 11:21:42AM +0200, Geert Uytterhoeven wrote:
> Turning a CRTC off will prevent a queued page flip from ever completing,
> potentially confusing userspace.  Wait for queued page flips to complete
> before turning the CRTC off to avoid this.
> 
> Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>

Given that you're duplicating the rcar-du page flip handling code, I
have a feeling core helpers would be handy. It's not a blocker for this
series though, so

Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@...asonboard.com>

> ---
>  .../gpu/drm/renesas/shmobile/shmob_drm_crtc.c | 37 +++++++++++++++++++
>  .../gpu/drm/renesas/shmobile/shmob_drm_crtc.h |  3 ++
>  2 files changed, 40 insertions(+)
> 
> diff --git a/drivers/gpu/drm/renesas/shmobile/shmob_drm_crtc.c b/drivers/gpu/drm/renesas/shmobile/shmob_drm_crtc.c
> index 1d7fcf64bf2aab80..d2a0ac5f9368c11c 100644
> --- a/drivers/gpu/drm/renesas/shmobile/shmob_drm_crtc.c
> +++ b/drivers/gpu/drm/renesas/shmobile/shmob_drm_crtc.c
> @@ -285,11 +285,40 @@ void shmob_drm_crtc_finish_page_flip(struct shmob_drm_crtc *scrtc)
>  	scrtc->event = NULL;
>  	if (event) {
>  		drm_crtc_send_vblank_event(&scrtc->base, event);
> +		wake_up(&scrtc->flip_wait);
>  		drm_crtc_vblank_put(&scrtc->base);
>  	}
>  	spin_unlock_irqrestore(&dev->event_lock, flags);
>  }
>  
> +static bool shmob_drm_crtc_page_flip_pending(struct shmob_drm_crtc *scrtc)
> +{
> +	struct drm_device *dev = scrtc->base.dev;
> +	unsigned long flags;
> +	bool pending;
> +
> +	spin_lock_irqsave(&dev->event_lock, flags);
> +	pending = scrtc->event != NULL;
> +	spin_unlock_irqrestore(&dev->event_lock, flags);
> +
> +	return pending;
> +}
> +
> +static void shmob_drm_crtc_wait_page_flip(struct shmob_drm_crtc *scrtc)
> +{
> +	struct drm_crtc *crtc = &scrtc->base;
> +	struct shmob_drm_device *sdev = to_shmob_device(crtc->dev);
> +
> +	if (wait_event_timeout(scrtc->flip_wait,
> +			       !shmob_drm_crtc_page_flip_pending(scrtc),
> +			       msecs_to_jiffies(50)))
> +		return;
> +
> +	dev_warn(sdev->dev, "page flip timeout\n");
> +
> +	shmob_drm_crtc_finish_page_flip(scrtc);
> +}
> +
>  /* -----------------------------------------------------------------------------
>   * CRTC Functions
>   */
> @@ -302,6 +331,12 @@ static void shmob_drm_crtc_stop(struct shmob_drm_crtc *scrtc)
>  	if (!scrtc->started)
>  		return;
>  
> +	/*
> +	 * Wait for page flip completion before stopping the CRTC as userspace
> +	 * expects page flips to eventually complete.
> +	 */
> +	shmob_drm_crtc_wait_page_flip(scrtc);
> +
>  	/* Stop the LCDC. */
>  	shmob_drm_crtc_start_stop(scrtc, false);
>  
> @@ -515,6 +550,8 @@ int shmob_drm_crtc_create(struct shmob_drm_device *sdev)
>  	unsigned int i;
>  	int ret;
>  
> +	init_waitqueue_head(&sdev->crtc.flip_wait);
> +
>  	sdev->crtc.dpms = DRM_MODE_DPMS_OFF;
>  
>  	primary = shmob_drm_plane_create(sdev, 0);
> diff --git a/drivers/gpu/drm/renesas/shmobile/shmob_drm_crtc.h b/drivers/gpu/drm/renesas/shmobile/shmob_drm_crtc.h
> index 2c6d7541427581a6..b9863e026e8a9b83 100644
> --- a/drivers/gpu/drm/renesas/shmobile/shmob_drm_crtc.h
> +++ b/drivers/gpu/drm/renesas/shmobile/shmob_drm_crtc.h
> @@ -14,6 +14,8 @@
>  #include <drm/drm_connector.h>
>  #include <drm/drm_encoder.h>
>  
> +#include <linux/wait.h>
> +
>  #include <video/videomode.h>
>  
>  struct drm_pending_vblank_event;
> @@ -24,6 +26,7 @@ struct shmob_drm_crtc {
>  	struct drm_crtc base;
>  
>  	struct drm_pending_vblank_event *event;
> +	wait_queue_head_t flip_wait;
>  	int dpms;
>  
>  	const struct shmob_drm_format_info *format;

-- 
Regards,

Laurent Pinchart