On Fri, 2018-07-13 at 14:22 -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?
>
> >
> > Some USB-C MST hubs cause us to get
> > stuck in this loop on hot-plugging indefinitely as
Also include the information (the vswing toggling part) about why it is
stuck in the loop.
> > 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@xxxxxxxxxxxxxxx>
> > ---
> > 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;
> }
>
> Thanks,
> Rodrigo.
>
> >
> > }
> > }
> >
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