Re: [PATCH 14/21] drm: mxsfb: Enable vblank handling

From: Stefan Agner <stefan@agner.ch>
To: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Marek Vasut <marex@denx.de>,
	kernel@pengutronix.de, dri-devel@lists.freedesktop.org,
	linux-imx@nxp.com
Subject: Re: [PATCH 14/21] drm: mxsfb: Enable vblank handling
Date: Tue, 24 Mar 2020 00:08:16 +0100	[thread overview]
Message-ID: <c6a1ff930152e17b61ec9e032fa7e4cb@agner.ch> (raw)
In-Reply-To: <20200309195216.31042-15-laurent.pinchart@ideasonboard.com>

On 2020-03-09 20:52, Laurent Pinchart wrote:
> Enable vblank handling when the CRTC is turned on and disable it when it
> is turned off. This requires moving vblank init after the KMS pipeline
> initialisation, otherwise drm_vblank_init() gets called with 0 CRTCs.
> 
> Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

With this patch applied I start to get system resets on my Colibri iMX7
test device during system boot shortly after initializing mxsfb. It
happens not on every boot, but rather often, I would say every second or
third. From what I can tell the interrupt handling should be safe, but
it seems that every now and then something races. Any idea what that
could be?

--
Stefan

> ---
>  drivers/gpu/drm/mxsfb/mxsfb_drv.c | 15 +++++++++------
>  drivers/gpu/drm/mxsfb/mxsfb_kms.c |  6 +++++-
>  2 files changed, 14 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/gpu/drm/mxsfb/mxsfb_drv.c
> b/drivers/gpu/drm/mxsfb/mxsfb_drv.c
> index e324bd2a63a5..72b4f6a947a4 100644
> --- a/drivers/gpu/drm/mxsfb/mxsfb_drv.c
> +++ b/drivers/gpu/drm/mxsfb/mxsfb_drv.c
> @@ -160,12 +160,6 @@ static int mxsfb_load(struct drm_device *drm,
> unsigned long flags)
>  
>  	pm_runtime_enable(drm->dev);
>  
> -	ret = drm_vblank_init(drm, drm->mode_config.num_crtc);
> -	if (ret < 0) {
> -		dev_err(drm->dev, "Failed to initialise vblank\n");
> -		goto err_vblank;
> -	}
> -
>  	/* Modeset init */
>  	drm_mode_config_init(drm);
>  
> @@ -175,6 +169,15 @@ static int mxsfb_load(struct drm_device *drm,
> unsigned long flags)
>  		goto err_vblank;
>  	}
>  
> +	ret = drm_vblank_init(drm, drm->mode_config.num_crtc);
> +	if (ret < 0) {
> +		dev_err(drm->dev, "Failed to initialise vblank\n");
> +		goto err_vblank;
> +	}
> +
> +	/* Start with vertical blanking interrupt reporting disabled. */
> +	drm_crtc_vblank_off(&mxsfb->crtc);
> +
>  	ret = mxsfb_attach_bridge(mxsfb);
>  	if (ret) {
>  		dev_err(drm->dev, "Cannot connect bridge: %d\n", ret);
> diff --git a/drivers/gpu/drm/mxsfb/mxsfb_kms.c
> b/drivers/gpu/drm/mxsfb/mxsfb_kms.c
> index ac2696c8483d..640305fb1068 100644
> --- a/drivers/gpu/drm/mxsfb/mxsfb_kms.c
> +++ b/drivers/gpu/drm/mxsfb/mxsfb_kms.c
> @@ -322,8 +322,10 @@ static void mxsfb_crtc_atomic_enable(struct drm_crtc *crtc,
>  	dma_addr_t paddr;
>  
>  	pm_runtime_get_sync(drm->dev);
> -
>  	mxsfb_enable_axi_clk(mxsfb);
> +
> +	drm_crtc_vblank_on(crtc);
> +
>  	mxsfb_crtc_mode_set_nofb(mxsfb);
>  
>  	/* Write cur_buf as well to avoid an initial corrupt frame */
> @@ -353,6 +355,8 @@ static void mxsfb_crtc_atomic_disable(struct drm_crtc *crtc,
>  	}
>  	spin_unlock_irq(&drm->event_lock);
>  
> +	drm_crtc_vblank_off(crtc);
> +
>  	mxsfb_disable_axi_clk(mxsfb);
>  	pm_runtime_put_sync(drm->dev);
>  }
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