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

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Date:   Wed, 26 Jun 2019 16:30:25 +0200
From:   Daniel Vetter <daniel@...ll.ch>
To:     Ville Syrjälä <ville.syrjala@...ux.intel.com>
Cc:     Robert Beckett <bob.beckett@...labora.com>,
        Maxime Ripard <maxime.ripard@...tlin.com>,
        Sean Paul <sean@...rly.run>, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, David Airlie <airlied@...ux.ie>,
        NXP Linux Team <linux-imx@....com>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Shawn Guo <shawnguo@...nel.org>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v3 3/4] drm/vblank: estimate vblank while disabling
 vblank if interrupt disabled

On Wed, Jun 26, 2019 at 04:27:32PM +0300, Ville Syrjälä wrote:
> 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.

Hm yeah we might need a power domain get/put around our
drm_crtc_vblank_off() call to make sure it dtrt. Revert sounds like a good
idea instead of adding more kludges ... a-b: me on the revert, even though
I did ack the original patch too.
-Daniel

> 
> > 
> > Signed-off-by: Robert Beckett <bob.beckett@...labora.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@...ts.freedesktop.org
> > https://lists.freedesktop.org/mailman/listinfo/dri-devel
> 
> -- 
> Ville Syrjälä
> Intel
> _______________________________________________
> dri-devel mailing list
> dri-devel@...ts.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/dri-devel

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

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