[Intel-gfx] [PATCH 1/2] drm/i915: Restore lost DPLL register write on gen2-4

[Ville Syrjälä]

On Thu, Oct 08, 2015 at 10:17:30AM +0200, Daniel Vetter wrote:
> On Wed, Oct 07, 2015 at 10:08:24PM +0300, ville.syrjala at linux.intel.com wrote:
> > From: Ville Syrjälä <ville.syrjala at linux.intel.com>
> > 
> > We accidentally lost the initial DPLL register write in
> > 1c4e02746147 drm/i915: Fix DVO 2x clock enable on 830M
> > 
> > The "three times for luck" hack probably saved us from a total
> > disaster. But anyway, bring the initial write back so that the
> > code actually makes some sense.
> > 
> > Cc: stable at vger.kernel.org
> > Cc: Nick Bowler <nbowler at draconx.ca>
> Reported-and-tested-by: Nick Bowler <nbowler at draconx.ca>
> References: http://lists.freedesktop.org/archives/intel-gfx/2015-October/077463.html
> 
> > Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
> > ---
> >  drivers/gpu/drm/i915/intel_display.c | 2 ++
> >  1 file changed, 2 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> > index 147e700..f4fdff9 100644
> > --- a/drivers/gpu/drm/i915/intel_display.c
> > +++ b/drivers/gpu/drm/i915/intel_display.c
> > @@ -1743,6 +1743,8 @@ static void i9xx_enable_pll(struct intel_crtc *crtc)
> >  			   I915_READ(DPLL(!crtc->pipe)) | DPLL_DVO_2X_MODE);
> 
> Don't we also need a POSTING_READ here to make sure the two-step 2x mode
> sequence is still followed?

We don't do write combining on registers, and there are no shadow
register type of things to consider in this case either.

> 
> With that addressed Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>
> >  	}
> >  
> > +	I915_WRITE(reg, dpll);
> > +
> >  	/* Wait for the clocks to stabilize. */
> >  	POSTING_READ(reg);
> >  	udelay(150);
> > -- 
> > 2.4.9
> > 
> > _______________________________________________
> > Intel-gfx mailing list
> > Intel-gfx at lists.freedesktop.org
> > http://lists.freedesktop.org/mailman/listinfo/intel-gfx
> 
> -- 
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch

-- 
Ville Syrjälä
Intel OTC