Re: [PATCH v3 3/4] drm/vblank: estimate vblank while disabling vblank if interrupt disabled

From: "Ville Syrjälä" <ville.syrjala@linux•intel.com>
To: Robert Beckett <bob.beckett@collabora•com>
Cc: Maxime Ripard <maxime.ripard@bootlin•com>,
	Sean Paul <sean@poorly•run>,
	linux-kernel@vger•kernel.org, dri-devel@lists•freedesktop.org,
	David Airlie <airlied@linux•ie>,
	NXP Linux Team <linux-imx@nxp•com>,
	Pengutronix Kernel Team <kernel@pengutronix•de>,
	Shawn Guo <shawnguo@kernel•org>,
	linux-arm-kernel@lists•infradead.org
Subject: Re: [PATCH v3 3/4] drm/vblank: estimate vblank while disabling vblank if interrupt disabled
Date: Wed, 26 Jun 2019 16:27:32 +0300	[thread overview]
Message-ID: <20190626132732.GP5942@intel.com> (raw)
In-Reply-To: <b96132cef4b63118df1026a99b3c345692e3de26.1561483965.git.bob.beckett@collabora.com>

On Tue, Jun 25, 2019 at 06:59:14PM +0100, Robert Beckett wrote:
> If interrupts are disabled (e.g. via vblank_disable_fn) and we come to
> disable vblank, update the vblank count to best guess as to what it
> would be had the interrupts remained enabled, and update the timesamp to
> now.
> 
> This avoids a stale vblank event being sent while disabling crtcs during
> atomic modeset.
> 
> Fixes: 68036b08b91bc ("drm/vblank: Do not update vblank count if interrupts
> are already disabled.")

I don't understand that commit. drm_vblank_off() should be called
when the power is still present, so it looks to me like that
commit is actually wrong. So I think we may want to just revert
it and figure out what the actual bug was.

> 
> Signed-off-by: Robert Beckett <bob.beckett@collabora•com>
> ---
>  drivers/gpu/drm/drm_vblank.c | 16 +++++++++++++++-
>  1 file changed, 15 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c
> index 7dabb2bdb733..db68b8cbf797 100644
> --- a/drivers/gpu/drm/drm_vblank.c
> +++ b/drivers/gpu/drm/drm_vblank.c
> @@ -375,9 +375,23 @@ void drm_vblank_disable_and_save(struct drm_device *dev, unsigned int pipe)
>  	 * interrupts were enabled. This avoids calling the ->disable_vblank()
>  	 * operation in atomic context with the hardware potentially runtime
>  	 * suspended.
> +	 * If interrupts are disabled (e.g. via blank_disable_fn) then make
> +	 * best guess as to what it would be now and make sure we have an up
> +	 * to date timestamp.
>  	 */
> -	if (!vblank->enabled)
> +	if (!vblank->enabled) {
> +		ktime_t now = ktime_get();
> +		u32 diff = 0;
> +		if (vblank->framedur_ns) {
> +			u64 diff_ns = ktime_to_ns(ktime_sub(now, vblank->time));
> +			diff = DIV_ROUND_CLOSEST_ULL(diff_ns,
> +						     vblank->framedur_ns);
> +		}
> +
> +		store_vblank(dev, pipe, diff, now, vblank->count);
> +
>  		goto out;
> +	}
>  
>  	/*
>  	 * Update the count and timestamp to maintain the
> -- 
> 2.18.0
> 
> _______________________________________________
> dri-devel mailing list
> dri-devel@lists•freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/dri-devel

-- 
Ville Syrjälä
Intel

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