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

[Jani Nikula <jani.nikula@linux.intel.com>]

On Thu, 08 Oct 2015, Ville Syrjälä <ville.syrjala@linux.intel.com> wrote:
> 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@linux.intel.com wrote:
>> > From: Ville Syrjälä <ville.syrjala@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@vger.kernel.org
>> > Cc: Nick Bowler <nbowler@draconx.ca>
>> Reported-and-tested-by: Nick Bowler <nbowler@draconx.ca>
>> References: http://lists.freedesktop.org/archives/intel-gfx/2015-October/077463.html
>> 
>> > Signed-off-by: Ville Syrjälä <ville.syrjala@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@ffwll.ch>


Daniel, are you happy with the responses about posting reads, for both
patches?

BR,
Jani.





>> >  	}
>> >  
>> > +	I915_WRITE(reg, dpll);
>> > +
>> >  	/* Wait for the clocks to stabilize. */
>> >  	POSTING_READ(reg);
>> >  	udelay(150);
>> > -- 
>> > 2.4.9
>> > 
>> > _______________________________________________
>> > Intel-gfx mailing list
>> > Intel-gfx@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
> _______________________________________________
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> Intel-gfx@lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/intel-gfx

-- 
Jani Nikula, Intel Open Source Technology Center