[Intel-gfx] [PATCH] drm/dp: Correctly mask DP_TRAINING_AUX_RD_INTERVAL values for DP 1.4

[Pandiyan, Dhinakaran]

On Tue, 2018-03-06 at 16:48 -0800, Dhinakaran Pandiyan wrote:
> 
> 
> On Tue, 2018-03-06 at 15:24 -0800, Rodrigo Vivi wrote:
> > On Tue, Mar 06, 2018 at 10:37:48AM -0800, matthew.s.atwood at intel.com wrote:
> > > From: Matt Atwood <matthew.s.atwood at intel.com>
> > > 
> > > DP_TRAINING_AUX_RD_INTERVAL with DP 1.3 spec changed bit scheme from 8
> > > bits to 7 bits in DPCD 0x000e. The 8th bit describes a new feature, for
> > > panels that use this new feature, this would cause a wait interval for
> > > clock recovery of at least 512 ms, much higher then spec maximum of 16 ms.
> > > This behavior is described in table 2-158 of DP 1.4 spec address 0000Eh.
> > > To avoid breaking panels 
> 
> See comment below:
> 
> > that are not spec compliant we now warn on
> > > invalid values.
> > > 
> > > V2: commit title/message, masking all 7 bits, warn on out of spec values.
> > 
> > this approach is even better imho.
> > 
> > > 
> > > Signed-off-by: Matt Atwood <matthew.s.atwood at intel.com>
> > 
> > Reviewed-by: Rodrigo Vivi <rodrigo.vivi at intel.com>
> > 
> > > ---
> > >  drivers/gpu/drm/drm_dp_helper.c | 18 ++++++++++++++----
> > >  include/drm/drm_dp_helper.h     |  1 +
> > >  2 files changed, 15 insertions(+), 4 deletions(-)
> > > 
> > > diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
> > > index adf79be..a718ccc 100644
> > > --- a/drivers/gpu/drm/drm_dp_helper.c
> > > +++ b/drivers/gpu/drm/drm_dp_helper.c
> > > @@ -119,18 +119,28 @@ 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]) {
> > > -	if (dpcd[DP_TRAINING_AUX_RD_INTERVAL] == 0)
> > > +	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)", rd_interval);
> 
> Some default for panels without a valid value?
> 		rd_interval = 4;
> 		"AUX read interval out of range, using max %d ms"
> 
> 	      
> > > +
> > > +	if (rd_interval == 0)
> > >  		udelay(100);
> > >  	else
> > > -		mdelay(dpcd[DP_TRAINING_AUX_RD_INTERVAL] * 4);
> > > +		mdelay(rd_interval * 4);

Btw, DP 1.4 spec also says this is 100 us for *all* values in the
register. Updating that for DP 1.4 panels should speed up link
training. 


> > >  }
> > >  EXPORT_SYMBOL(drm_dp_link_train_clock_recovery_delay);
> > >  
> > >  void drm_dp_link_train_channel_eq_delay(const u8 dpcd[DP_RECEIVER_CAP_SIZE]) {
> > > -	if (dpcd[DP_TRAINING_AUX_RD_INTERVAL] == 0)
> > > +	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)", rd_interval);
> > > +
> > > +	if (rd_interval == 0)
> > >  		udelay(400);
> > >  	else
> > > -		mdelay(dpcd[DP_TRAINING_AUX_RD_INTERVAL] * 4);
> > > +		mdelay(rd_interval * 4);
> > >  }
> > >  EXPORT_SYMBOL(drm_dp_link_train_channel_eq_delay);
> > >  
> > > diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h
> > > index da58a42..f80acf1 100644
> > > --- a/include/drm/drm_dp_helper.h
> > > +++ b/include/drm/drm_dp_helper.h
> > > @@ -118,6 +118,7 @@
> > >  # define DP_DPCD_DISPLAY_CONTROL_CAPABLE     (1 << 3) /* edp v1.2 or higher */
> > >  
> > >  #define DP_TRAINING_AUX_RD_INTERVAL         0x00e   /* XXX 1.2? */
> > > +# define DP_TRAINING_AUX_RD_MASK            0x7F     /* 1.3 */
> > >  
> > >  #define DP_ADAPTER_CAP			    0x00f   /* 1.2 */
> > >  # define DP_FORCE_LOAD_SENSE_CAP	    (1 << 0)
> > > -- 
> > > 2.7.4
> > > 
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