Re: [PATCH 1/4] drm/i915: Avoid EBUSY retry on intel_dp_aux_ch.

["Vivi, Rodrigo" <rodrigo.vivi@intel.com>]

On Wed, 2015-10-21 at 23:31 +0530, Thulasimani, Sivakumar wrote:
> 
> On 10/21/2015 7:54 PM, Vivi, Rodrigo wrote:
> > On Wed, 2015-10-21 at 12:19 +0300, Ville Syrjälä wrote:
> > > On Wed, Oct 21, 2015 at 10:28:51AM -0700, Rodrigo Vivi wrote:
> > > > EBUSY retries are already in place at drm level.
> > > > We don't need to replicate the job here.
> > > > 
> > > > Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
> > > > ---
> > > >   drivers/gpu/drm/i915/intel_dp.c | 20 ++------------------
> > > >   1 file changed, 2 insertions(+), 18 deletions(-)
> > > > 
> > > > diff --git a/drivers/gpu/drm/i915/intel_dp.c
> > > > b/drivers/gpu/drm/i915/intel_dp.c
> > > > index 09bdd94..d054129 100644
> > > > --- a/drivers/gpu/drm/i915/intel_dp.c
> > > > +++ b/drivers/gpu/drm/i915/intel_dp.c
> > > > @@ -818,24 +818,8 @@ intel_dp_aux_ch(struct intel_dp *intel_dp,
> > > >   
> > > >   	intel_aux_display_runtime_get(dev_priv);
> > > >   
> > > > -	/* Try to wait for any previous AUX channel activity 
> > > > */
> > > > -	for (try = 0; try < 3; try++) {
> > > > -		status = I915_READ_NOTRACE(ch_ctl);
> > > > -		if ((status & DP_AUX_CH_CTL_SEND_BUSY) == 0)
> > > > -			break;
> > > > -		msleep(1);
> > > The dp helper doesn't sleep at all between the retries, so 
> > > dropping
> > > the
> > > sleep from here may change the behaviour.
> > hm indeed... what about
> > + msleep(1);
> > + ret = -EBUSY
> > + goto out;
> > ?
> the current code is one of few test cases that pass during compliance 
> testing
> so please confirm this change does not break that :).

which one specifically are you telling about?
anyway basic tests here were at the same rate (128 pass/skip and 2
fails on bdw 1 fail on skl) without and with this series.

> 
> regards,
> Sivakumar
> > > > -	}
> > > > -
> > > > -	if (try == 3) {
> > > > -		static u32 last_status = -1;
> > > > -		const u32 status = I915_READ(ch_ctl);
> > > > -
> > > > -		if (status != last_status) {
> > > > -			WARN(1, "dp_aux_ch not started status
> > > > 0x%08x\n",
> > > > -			     status);
> > > > -			last_status = status;
> > > > -		}
> > > > -
> > > > +	status = I915_READ_NOTRACE(ch_ctl);
> > > > +	if ((status & DP_AUX_CH_CTL_SEND_BUSY) != 0) {
> > > >   		ret = -EBUSY;
> > > >   		goto out;
> > > >   	}
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