[Intel-gfx] [PATCH] drm/i915/dp: Poll for DDI Idle status to be 0 after enabling DDI Buf

[Manasi Navare]

On Tue, Jun 16, 2020 at 11:22:32PM +0300, Ville Syrjälä wrote:
> On Tue, Jun 16, 2020 at 12:30:56PM -0700, Manasi Navare wrote:
> > The Bspec sequence expects us to poll for DDI Idle status
> > to be 0 (not idle) with a timeout of 600usecs after enabling the
> > DDI BUF CTL. But currently in the driver we just wait for 600usecs
> > without polling so add that.
> > 
> > Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
> > Cc: Imre Deak <imre.deak at intel.com>
> > Signed-off-by: Manasi Navare <manasi.d.navare at intel.com>
> > ---
> >  drivers/gpu/drm/i915/display/intel_ddi.c | 6 +++++-
> >  1 file changed, 5 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/display/intel_ddi.c b/drivers/gpu/drm/i915/display/intel_ddi.c
> > index ca7bb2294d2b..de7e15de0bc5 100644
> > --- a/drivers/gpu/drm/i915/display/intel_ddi.c
> > +++ b/drivers/gpu/drm/i915/display/intel_ddi.c
> > @@ -4023,7 +4023,11 @@ static void intel_ddi_prepare_link_retrain(struct intel_dp *intel_dp)
> >  	intel_de_write(dev_priv, DDI_BUF_CTL(port), intel_dp->DP);
> >  	intel_de_posting_read(dev_priv, DDI_BUF_CTL(port));
> >  
> > -	udelay(600);
> > +	if (wait_for_us(!(intel_de_read(dev_priv, DDI_BUF_CTL(port)) &
> > +			  DDI_BUF_IS_IDLE),
> > +			600))
> > +		drm_err(&dev_priv->drm, "DDI port:%c buffer idle\n",
> > +			port_name(port));
> 
> Another thing I just noticed is that icl+ need this for HDMI as well.
> The slightly odd thing is that glk is documented to need this for
> DP but not HDMI. But I'm thinking doing it also for glk HDMI should
> be fine.
> 
> So I guess to line up with the spec we should:
> - fixed >518us enable delay for pre-glk (not sure if polling
>   would be ok for hsw/bdw/skl)
> - poll for enable on glk+
> - fixed 16us disable delay for bxt
> - poll for disable on !bxt
> 
> And do it for both DP and HDMI for consistency.

So since its different one each platform, should we create a per platform hook
like wait_for_non_idle_status or something per platform?

Manasi

> 
> 
> >  }
> >  
> >  static void intel_ddi_set_link_train(struct intel_dp *intel_dp,
> > -- 
> > 2.19.1
> 
> -- 
> Ville Syrjälä
> Intel