[Intel-gfx] [PATCH] drm/i915/dp: Give up link training clock recovery after 10 failed attempts

[Nathan Ciobanu]

On Fri, Jul 13, 2018 at 02:22:03PM -0700, Rodrigo Vivi wrote:
> On Fri, Jul 13, 2018 at 10:32:15AM -0700, Nathan Ciobanu wrote:
> > Limit the link training clock recovery loop to 10 failed attempts at
> > LANEx_CR_DONE per DP 1.4 spec.
> 
> Where exactly in the spec?
I'll add the section number to the commit message.
> 
> > Some USB-C MST hubs cause us to get
> > stuck in this loop on hot-plugging indefinitely as
> > drm_dp_clock_recovery_ok() never returns true and none of the
> > other conditions occur.
> 
> Although it seems really bad situation that we need to avoid...
> 
> > 
> > Signed-off-by: Nathan Ciobanu <nathan.d.ciobanu at linux.intel.com>
> > ---
> >  drivers/gpu/drm/i915/intel_dp_link_training.c | 8 +++++++-
> >  1 file changed, 7 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/intel_dp_link_training.c b/drivers/gpu/drm/i915/intel_dp_link_training.c
> > index 4da6e33c7fa1..66c1a70343ba 100644
> > --- a/drivers/gpu/drm/i915/intel_dp_link_training.c
> > +++ b/drivers/gpu/drm/i915/intel_dp_link_training.c
> > @@ -129,7 +129,7 @@ static bool intel_dp_link_max_vswing_reached(struct intel_dp *intel_dp)
> >  intel_dp_link_training_clock_recovery(struct intel_dp *intel_dp)
> >  {
> >  	uint8_t voltage;
> > -	int voltage_tries, max_vswing_tries;
> > +	int voltage_tries, max_vswing_tries, cr_tries;
> >  	uint8_t link_config[2];
> >  	uint8_t link_bw, rate_select;
> >  
> > @@ -172,6 +172,7 @@ static bool intel_dp_link_max_vswing_reached(struct intel_dp *intel_dp)
> >  
> >  	voltage_tries = 1;
> >  	max_vswing_tries = 0;
> > +	cr_tries = 0;
> >  	for (;;) {
> >  		uint8_t link_status[DP_LINK_STATUS_SIZE];
> >  
> > @@ -215,6 +216,11 @@ static bool intel_dp_link_max_vswing_reached(struct intel_dp *intel_dp)
> >  		if (intel_dp_link_max_vswing_reached(intel_dp))
> >  			++max_vswing_tries;
> >  
> > +		if (cr_tries == 9) {
> > +			DRM_ERROR("Failed clock recovery 10 times, giving up!\n");
> > +			return false;
> > +		}
> > +		++cr_tries;
> 
> If I understood correctly this is a global thing for the for(;;) right?
> 
> Shouldn't we make then like a:
> 
> - for(;;)
> + for(cr_tries = 0; cr_tries < 10; cr_tries++)
> 	{
> 	}
> 
> + DRM_ERROR("Failed clock recovery 10 times, giving up!\n"); 
> + return false;
> }
That was my thought initially as well but I was worried that
it will not be immediately obvious why I'm returning false after
the loop - although the error message tells you why. I'll change
this. 

-Nathan
> 
> Thanks,
> Rodrigo.
> 
> >  	}
> >  }
> >  
> > -- 
> > 1.9.1
> > 
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>