Re: [PATCH v2] drm/i915/hsw: Add display Audio codec disable sequence for Haswell

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Wed, Sep 04, 2013 at 08:50:13PM +0200, Daniel Vetter wrote:
> On Fri, Aug 30, 2013 at 1:50 AM,  <mengdong.lin@intel.com> wrote:
> > +       /* Wait for 2 vertical blanks */
> > +       intel_wait_for_vblank(dev, pipe);
> > +       intel_wait_for_vblank(dev, pipe);
> > +
> > +       /* Disable audio PD. This is optional as per Bspec.  */
> > +       temp = I915_READ(HSW_AUD_PIN_ELD_CP_VLD);
> > +       temp &= ~(AUDIO_OUTPUT_ENABLE_A << (pipe * 4));
> > +       I915_WRITE(HSW_AUD_PIN_ELD_CP_VLD, temp);
> 
> If this is optional do we really need the two vblank waits above?
> Adding them just for fun when we generally try to rip out as many
> vblank waits as possible from the modeset code isn't all that great
> ...

One idea I had for these kinds of vblank waits (there also one required
for IPS for instance) is that we might just sample a vblank counter
after the first step, then at the latest point we can, we'd wait for the
frame counter to have passed the sampled vaoue + whatever extra is
needed. That might allow us to do other stuff in parallel while the
required number of vblanks will elapese.

-- 
Ville Syrjälä
Intel OTC