[PATCH 07/15] drm/dp: Do not busy-loop during link training

[Thierry Reding]

On Fri, Oct 18, 2019 at 05:31:19PM -0400, Lyude Paul wrote:
> On Tue, 2019-10-15 at 16:35 +0200, Thierry Reding wrote:
> > From: Thierry Reding <treding at nvidia.com>
> > 
> > Use microsecond sleeps for the clock recovery and channel equalization
> > delays during link training. The duration of these delays can be from
> > 100 us up to 16 ms. It is rude to busy-loop for that amount of time.
> > 
> > While at it, also convert to standard coding style by putting the
> > opening braces in a function definition on a new line.
> > 
> > v2: use correct multiplier for training delays (Philipp Zabel)
> > 
> > Signed-off-by: Thierry Reding <treding at nvidia.com>
> > ---
> >  drivers/gpu/drm/drm_dp_helper.c | 30 ++++++++++++++++++------------
> >  1 file changed, 18 insertions(+), 12 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/drm_dp_helper.c
> > b/drivers/gpu/drm/drm_dp_helper.c
> > index 8f2d7c4850ca..ad2671d2ee8f 100644
> > --- a/drivers/gpu/drm/drm_dp_helper.c
> > +++ b/drivers/gpu/drm/drm_dp_helper.c
> > @@ -120,33 +120,39 @@ u8 drm_dp_get_adjust_request_pre_emphasis(const u8
> > link_status[DP_LINK_STATUS_SI
> >  }
> >  EXPORT_SYMBOL(drm_dp_get_adjust_request_pre_emphasis);
> >  
> > -void drm_dp_link_train_clock_recovery_delay(const u8
> > dpcd[DP_RECEIVER_CAP_SIZE]) {
> > -	int rd_interval = dpcd[DP_TRAINING_AUX_RD_INTERVAL] &
> > -			  DP_TRAINING_AUX_RD_MASK;
> > +void drm_dp_link_train_clock_recovery_delay(const u8
> > dpcd[DP_RECEIVER_CAP_SIZE])
> > +{
> > +	unsigned int rd_interval = dpcd[DP_TRAINING_AUX_RD_INTERVAL] &
> > +					DP_TRAINING_AUX_RD_MASK;
> 
> Did you mean to put this conversion from signed to unsigned in the previous
> patch?

It doesn't really belong in the previous patch, though I guess it might
be better in the subsequent patch where the new interval helper is used
from this function.

Thierry

> 
> >  
> >  	if (rd_interval > 4)
> > -		DRM_DEBUG_KMS("AUX interval %d, out of range (max 4)\n",
> > +		DRM_DEBUG_KMS("AUX interval %u, out of range (max 4)\n",
> >  			      rd_interval);
> >  
> >  	if (rd_interval == 0 || dpcd[DP_DPCD_REV] >= DP_DPCD_REV_14)
> > -		udelay(100);
> > +		rd_interval = 100;
> >  	else
> > -		mdelay(rd_interval * 4);
> > +		rd_interval *= 4 * USEC_PER_MSEC;
> > +
> > +	usleep_range(rd_interval, rd_interval * 2);
> >  }
> >  EXPORT_SYMBOL(drm_dp_link_train_clock_recovery_delay);
> >  
> > -void drm_dp_link_train_channel_eq_delay(const u8
> > dpcd[DP_RECEIVER_CAP_SIZE]) {
> > -	int rd_interval = dpcd[DP_TRAINING_AUX_RD_INTERVAL] &
> > -			  DP_TRAINING_AUX_RD_MASK;
> > +void drm_dp_link_train_channel_eq_delay(const u8
> > dpcd[DP_RECEIVER_CAP_SIZE])
> > +{
> > +	unsigned int rd_interval = dpcd[DP_TRAINING_AUX_RD_INTERVAL] &
> > +					DP_TRAINING_AUX_RD_MASK;
> >  
> >  	if (rd_interval > 4)
> > -		DRM_DEBUG_KMS("AUX interval %d, out of range (max 4)\n",
> > +		DRM_DEBUG_KMS("AUX interval %u, out of range (max 4)\n",
> >  			      rd_interval);
> >  
> >  	if (rd_interval == 0)
> > -		udelay(400);
> > +		rd_interval = 400;
> >  	else
> > -		mdelay(rd_interval * 4);
> > +		rd_interval *= 4 * USEC_PER_MSEC;
> > +
> > +	usleep_range(rd_interval, rd_interval * 2);
> >  }
> >  EXPORT_SYMBOL(drm_dp_link_train_channel_eq_delay);
> >  
> -- 
> Cheers,
> 	Lyude Paul
> 
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