[PATCH] drm/i915: drop buggy write to FDI_RX_CHICKEN register

[PATCH] drm/i915: drop buggy write to FDI_RX_CHICKEN register

[Daniel Vetter]

Jani Nikula noticed that the parentheses are wrong and we & the bit
with the register address instead of the read-back value. He sent a
patch to correct that.

On second look, we write the same register in the previous line, and
the w/a seems to be to set FDI_RX_PHASE_SYNC_POINTER_OVR to enable the
logic, then keep always set FDI_RX_PHASE_SYNC_POINTER_OVR and toggle
~FDI_RX_PHASE_SYNC_POINTER_EN before/after enabling the pc transcoder.

So the right things seems to be to simply kill the 2nd write.

Cc: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
---
 drivers/gpu/drm/i915/intel_display.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index f95d537..ed79e51 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -2924,9 +2924,6 @@ static void ironlake_fdi_disable(struct drm_crtc *crtc)
 	/* Ironlake workaround, disable clock pointer after downing FDI */
 	if (HAS_PCH_IBX(dev)) {
 		I915_WRITE(FDI_RX_CHICKEN(pipe), FDI_RX_PHASE_SYNC_POINTER_OVR);
-		I915_WRITE(FDI_RX_CHICKEN(pipe),
-			   I915_READ(FDI_RX_CHICKEN(pipe) &
-				     ~FDI_RX_PHASE_SYNC_POINTER_EN));
 	} else if (HAS_PCH_CPT(dev)) {
 		cpt_phase_pointer_disable(dev, pipe);
 	}
-- 
1.7.11.4

Re: [PATCH] drm/i915: drop buggy write to FDI_RX_CHICKEN register

[Chris Wilson]

On Wed, 14 Nov 2012 17:47:39 +0100, Daniel Vetter <daniel.vetter@ffwll.ch> wrote:
> Jani Nikula noticed that the parentheses are wrong and we & the bit
> with the register address instead of the read-back value. He sent a
> patch to correct that.
> 
> On second look, we write the same register in the previous line, and
> the w/a seems to be to set FDI_RX_PHASE_SYNC_POINTER_OVR to enable the
> logic, then keep always set FDI_RX_PHASE_SYNC_POINTER_OVR and toggle
> ~FDI_RX_PHASE_SYNC_POINTER_EN before/after enabling the pc transcoder.
> 
> So the right things seems to be to simply kill the 2nd write.
> 
> Cc: Jani Nikula <jani.nikula@intel.com>
> Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

Looks sane(r).
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre

Re: [PATCH] drm/i915: drop buggy write to FDI_RX_CHICKEN register

[Daniel Vetter]

On Thu, Nov 15, 2012 at 10:42:02AM +0000, Chris Wilson wrote:
> On Wed, 14 Nov 2012 17:47:39 +0100, Daniel Vetter <daniel.vetter@ffwll.ch> wrote:
> > Jani Nikula noticed that the parentheses are wrong and we & the bit
> > with the register address instead of the read-back value. He sent a
> > patch to correct that.
> > 
> > On second look, we write the same register in the previous line, and
> > the w/a seems to be to set FDI_RX_PHASE_SYNC_POINTER_OVR to enable the
> > logic, then keep always set FDI_RX_PHASE_SYNC_POINTER_OVR and toggle
> > ~FDI_RX_PHASE_SYNC_POINTER_EN before/after enabling the pc transcoder.
> > 
> > So the right things seems to be to simply kill the 2nd write.
> > 
> > Cc: Jani Nikula <jani.nikula@intel.com>
> > Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> 
> Looks sane(r).
> Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Queued for -next, thanks for the review.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch