[Intel-gfx] [PATCH] drm/i915: HDCP: retry link integrity check on failure

[Oliver Barta]

On Tue, May 5, 2020 at 9:38 AM Ramalingam C <ramalingam.c at intel.com> wrote:
>
> On 2020-05-04 at 14:35:24 +0200, Oliver Barta wrote:
> > From: Oliver Barta <oliver.barta at aptiv.com>
> >
> > A single Ri mismatch doesn't automatically mean that the link integrity
> > is broken. Update and check of Ri and Ri' are done asynchronously. In
> > case an update happens just between the read of Ri' and the check against
> > Ri there will be a mismatch even if the link integrity is fine otherwise.
>
> Thanks for working on this. Btw, did you face this sporadic link check
> failure or theoretically you are fixing it?
>
> IMO this change will rule out possible sporadic link check failures as
> mentioned in the commit msg. Though I haven't faced this issue at my
> testings.
>
> Reviewed-by: Ramalingam C <ramalingam.c at intel.com>
>

I found it by code inspection, the probability for this to happen is
very low. In order to test the patch I'm decreasing the value of
DRM_HDCP_CHECK_PERIOD_MS to just a few ms. Once you do that it happens
every few seconds.

Thanks,
Oliver

> >
> > Signed-off-by: Oliver Barta <oliver.barta at aptiv.com>
> > ---
> >  drivers/gpu/drm/i915/display/intel_hdmi.c | 19 ++++++++++++++++---
> >  1 file changed, 16 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/display/intel_hdmi.c b/drivers/gpu/drm/i915/display/intel_hdmi.c
> > index 010f37240710..3156fde392f2 100644
> > --- a/drivers/gpu/drm/i915/display/intel_hdmi.c
> > +++ b/drivers/gpu/drm/i915/display/intel_hdmi.c
> > @@ -1540,7 +1540,7 @@ int intel_hdmi_hdcp_toggle_signalling(struct intel_digital_port *intel_dig_port,
> >  }
> >
> >  static
> > -bool intel_hdmi_hdcp_check_link(struct intel_digital_port *intel_dig_port)
> > +bool intel_hdmi_hdcp_check_link_once(struct intel_digital_port *intel_dig_port)
> >  {
> >       struct drm_i915_private *i915 = to_i915(intel_dig_port->base.base.dev);
> >       struct intel_connector *connector =
> > @@ -1563,8 +1563,7 @@ bool intel_hdmi_hdcp_check_link(struct intel_digital_port *intel_dig_port)
> >       if (wait_for((intel_de_read(i915, HDCP_STATUS(i915, cpu_transcoder, port)) &
> >                     (HDCP_STATUS_RI_MATCH | HDCP_STATUS_ENC)) ==
> >                    (HDCP_STATUS_RI_MATCH | HDCP_STATUS_ENC), 1)) {
> > -             drm_err(&i915->drm,
> > -                     "Ri' mismatch detected, link check failed (%x)\n",
> > +             drm_dbg_kms(&i915->drm, "Ri' mismatch detected (%x)\n",
> >                       intel_de_read(i915, HDCP_STATUS(i915, cpu_transcoder,
> >                                                       port)));
> >               return false;
> > @@ -1572,6 +1571,20 @@ bool intel_hdmi_hdcp_check_link(struct intel_digital_port *intel_dig_port)
> >       return true;
> >  }
> >
> > +static
> > +bool intel_hdmi_hdcp_check_link(struct intel_digital_port *intel_dig_port)
> > +{
> > +     struct drm_i915_private *i915 = to_i915(intel_dig_port->base.base.dev);
> > +     int retry;
> > +
> > +     for (retry = 0; retry < 3; retry++)
> > +             if (intel_hdmi_hdcp_check_link_once(intel_dig_port))
> > +                     return true;
> > +
> > +     drm_err(&i915->drm, "Link check failed\n");
> > +     return false;
> > +}
> > +
> >  struct hdcp2_hdmi_msg_timeout {
> >       u8 msg_id;
> >       u16 timeout;
> > --
> > 2.20.1
> >