linux-kernel - Re: [PATCH 5.2 048/215] drm/omap: dont check dispc timings for DSI

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Message-ID: <20190730141448.hvmkffa4s23pweci@earth.universe>
Date:   Tue, 30 Jul 2019 16:14:48 +0200
From:   Sebastian Reichel <sebastian.reichel@...labora.com>
To:     Pavel Machek <pavel@...x.de>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Tony Lindgren <tony@...mide.com>,
        Tomi Valkeinen <tomi.valkeinen@...com>,
        Sasha Levin <sashal@...nel.org>
Subject: Re: [PATCH 5.2 048/215] drm/omap: dont check dispc timings for DSI

Hi,

On Tue, Jul 30, 2019 at 01:37:51PM +0200, Pavel Machek wrote:
> On Mon 2019-07-29 21:20:44, Greg Kroah-Hartman wrote:
> > [ Upstream commit ad9df7d91b4a6e8f4b20c2bf539ac09b3b2ad6eb ]
> > 
> > While most display types only forward their VM to the DISPC, this
> > is not true for DSI. DSI calculates the VM for DISPC based on its
> > own, but it's not identical. Actually the DSI VM is not even a valid
> > DISPC VM making this check fail. Let's restore the old behaviour
> > and avoid checking the DISPC VM for DSI here.
> > 
> > Fixes: 7c27fa57ef31 ("drm/omap: Call dispc timings check operation directly")
> > Acked-by: Pavel Machek <pavel@....cz>
> > Tested-by: Tony Lindgren <tony@...mide.com>
> > Tested-by: Pavel Machek <pavel@....cz>
> > Signed-off-by: Sebastian Reichel <sebastian.reichel@...labora.com>
> > Signed-off-by: Tomi Valkeinen <tomi.valkeinen@...com>
> > Signed-off-by: Sasha Levin <sashal@...nel.org>
> 
> Not sure if this is good idea for stable. IIRC there's series of
> patches to enable display on droid4 (etc), which is useful, but this
> patch is not going to do any good on its own.

It does not hurt to have it. I know that some people have out of
tree omapdrm DSI drivers and those also need this regression fix.

-- Sebastian

> 
> 								Pavel
> 
> >  drivers/gpu/drm/omapdrm/omap_crtc.c | 18 ++++++++++++++----
> >  1 file changed, 14 insertions(+), 4 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/omapdrm/omap_crtc.c b/drivers/gpu/drm/omapdrm/omap_crtc.c
> > index 8712af79a49c..4c43dd282acc 100644
> > --- a/drivers/gpu/drm/omapdrm/omap_crtc.c
> > +++ b/drivers/gpu/drm/omapdrm/omap_crtc.c
> > @@ -384,10 +384,20 @@ static enum drm_mode_status omap_crtc_mode_valid(struct drm_crtc *crtc,
> >  	int r;
> >  
> >  	drm_display_mode_to_videomode(mode, &vm);
> > -	r = priv->dispc_ops->mgr_check_timings(priv->dispc, omap_crtc->channel,
> > -					       &vm);
> > -	if (r)
> > -		return r;
> > +
> > +	/*
> > +	 * DSI might not call this, since the supplied mode is not a
> > +	 * valid DISPC mode. DSI will calculate and configure the
> > +	 * proper DISPC mode later.
> > +	 */
> > +	if (omap_crtc->pipe->output->next == NULL ||
> > +	    omap_crtc->pipe->output->next->type != OMAP_DISPLAY_TYPE_DSI) {
> > +		r = priv->dispc_ops->mgr_check_timings(priv->dispc,
> > +						       omap_crtc->channel,
> > +						       &vm);
> > +		if (r)
> > +			return r;
> > +	}
> >  
> >  	/* Check for bandwidth limit */
> >  	if (priv->max_bandwidth) {
> 
> -- 
> (english) http://www.livejournal.com/~pavelmachek
> (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html



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