Re: [PATCH] drm/i915: Simplify the way BC bifurcation state consistency is kept

From: Daniel Vetter <daniel@ffwll.ch>
To: "Ville Syrjälä" <ville.syrjala@linux.intel.com>
Cc: "Conselvan De Oliveira,
	Ander" <ander.conselvan.de.oliveira@intel.com>,
	"intel-gfx@lists.freedesktop.org"
	<intel-gfx@lists.freedesktop.org>
Subject: Re: [PATCH] drm/i915: Simplify the way BC bifurcation state consistency is kept
Date: Wed, 11 Mar 2015 21:42:48 +0100	[thread overview]
Message-ID: <20150311204248.GP3800@phenom.ffwll.local> (raw)
In-Reply-To: <20150311165812.GV11371@intel.com>

On Wed, Mar 11, 2015 at 06:58:12PM +0200, Ville Syrjälä wrote:
> On Wed, Mar 11, 2015 at 11:37:54AM +0000, Conselvan De Oliveira, Ander wrote:
> > On Wed, 2015-03-11 at 13:35 +0200, Ander Conselvan de Oliveira wrote:
> > > Remove the global modeset resource function that would disable the
> > > bifurcation bit, and instead enable/disable it when enabling the pch
> > > transcoder. The mode set consistency check should prevent us from
> > > disabling the bit if pipe C is enabled so the change should be safe.
> > > 
> > > Note that this doens't affect the logic that prevents the bit being
> > > set while a pipe is active, since the patch retains the behavior of
> > > only chaging the bit if necessary. Because of the checks during mode
> > > set, the first change would necessarily happen with both pipes B and
> > > C disabled, and any subsequent write would be skipped.
> > > 
> > > v2: Only change the bit during pch trancoder enable. (Ville)
> > 
> > Oops, I forgot the sob line.
> > 
> > Signed-off-by: Ander Conselvan de Oliveira
> > <ander.conselvan.de.oliveira@intel.com>
> 
> 
> So I was staring at this stuff for a while and I believe it should be
> fine. We don't keep the bifurcation state entirely consistent when
> neither of the the pipes B/C are actually driving a PCH transcoder, but
> that shouldn't really matter. If we want to make it consistent then I
> suggest that we go with my earlier idea of only changing the state at
> transcoder B with >2 lanes enable/disable, and otherwise keep it enabled
> all the time. The slight complication there is the initial state we get
> from the BIOS which might not match that, so we'd need to sanitize it
> or something.
> 
> Anyway, I also posted a couple of patches on top that try to sort out
> ironlake_check_fdi_lanes() [1]. With those and this one I think things
> should work even better than before.
> 
> So for this patch:
> Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

Queued for -next, thanks for the patch.
-Daniel
>-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch
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