Re: [PATCH] drm/i915/hdcp: Avoid duplicate HDCP enables

[Sean Paul <sean@poorly.run>]

On Thu, May 21, 2020 at 5:36 AM Anshuman Gupta <anshuman.gupta@intel.com> wrote:
>
> On 2020-05-21 at 10:27:21 +0530, Ramalingam C wrote:
> > On 2020-05-20 at 15:47:44 -0400, Sean Paul wrote:
> > > From: Sean Paul <seanpaul@chromium.org>
> > >
> > > If userspace sets the CP property to DESIRED while it's already ENABLED,
> > > the driver will try to re-enable HDCP. On some displays, this will
> > > result in R0' mismatches. I'm guessing this is because the display is
> > > still sending back Ri instead of re-authenticating.
> > >
> > > At any rate, we can fix this inefficiency easily enough by just nooping
> > > the DESIRED property set if HDCP is already ENABLED.
> AFAIU may below patch also solves above issue implicitly.
> https://patchwork.freedesktop.org/patch/365758/?series=72251&rev=4
> Besides that +1 for below Ram comment, it would be better if such type of duplicate
> enable request should filter by drm_atomic_connector_set_property().

Thanks Anshuman, I didn't see that patch. Indeed that seems like it
accomplishes the same thing.

Let's drop this.

Sean

> Thanks,
> Anshuman Gupta.
>
> > Sean,
> >
> > This will skip the hdcp enable.
> >
> > But at present too we will be getting below WARN_ON from intel_hdcp_enable,
> > to indicate userspace is going wrong with request.
> >         drm_WARN_ON(&dev_priv->drm,
> >                     hdcp->value == DRM_MODE_CONTENT_PROTECTION_ENABLED);
> >
> > And if we need to filter this out, could we validate the incoming hdcp request at
> > drm_atomic_connector_set_property() itself? No point in going into the
> > atomic commit without a valid request. something like
> >
> > diff --git a/drivers/gpu/drm/drm_atomic_uapi.c b/drivers/gpu/drm/drm_atomic_uapi.c
> > index a1e5e262bae2..d98b2eeae78d 100644
> > --- a/drivers/gpu/drm/drm_atomic_uapi.c
> > +++ b/drivers/gpu/drm/drm_atomic_uapi.c
> > @@ -746,6 +746,12 @@ static int drm_atomic_connector_set_property(struct drm_connector *connector,
> >                         DRM_DEBUG_KMS("only drivers can set CP Enabled\n");
> >                         return -EINVAL;
> >                 }
> > +               if (config->content_protection_property ==
> > +                   DRM_MODE_CONTENT_PROTECTION_ENABLED &&
> > +                   val == DRM_MODE_CONTENT_PROTECTION_DESIRED) {
> > +                       DRM_DEBUG_KMS("Redundant req for content protection\n");
> > +                       return -EINVAL;
> > +               }
> >                 state->content_protection = val;
> >         } else if (property == config->hdcp_content_type_property) {
> >                 state->hdcp_content_type = val;
> >
> > -Ram
> >
> > >
> > > Signed-off-by: Sean Paul <seanpaul@chromium.org>
> > > ---
> > >
> > > I suspect this is the actual root cause I was chasing with
> > > "drm/i915/hdcp: Add additional R0' wait". I was able to reproduce the
> > > R0` messages by marking HDCP desired while it was already enabled. This
> > > _should_ work, but it seems like some displays handle it more graciously
> > > than others.
> > >
> > >
> > >  drivers/gpu/drm/i915/display/intel_hdcp.c | 10 +++++++---
> > >  1 file changed, 7 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/drivers/gpu/drm/i915/display/intel_hdcp.c b/drivers/gpu/drm/i915/display/intel_hdcp.c
> > > index 2cbc4619b4ce..f770fe0c5595 100644
> > > --- a/drivers/gpu/drm/i915/display/intel_hdcp.c
> > > +++ b/drivers/gpu/drm/i915/display/intel_hdcp.c
> > > @@ -2156,12 +2156,16 @@ void intel_hdcp_atomic_check(struct drm_connector *connector,
> > >     }
> > >
> > >     /*
> > > -    * Nothing to do if the state didn't change, or HDCP was activated since
> > > -    * the last commit. And also no change in hdcp content type.
> > > +    * Nothing to do if content type is unchanged and one of:
> > > +    *  - state didn't change
> > > +    *  - HDCP was activated since the last commit
> > > +    *  - attempting to set to desired while already enabled
> > >      */
> > >     if (old_cp == new_cp ||
> > >         (old_cp == DRM_MODE_CONTENT_PROTECTION_DESIRED &&
> > > -        new_cp == DRM_MODE_CONTENT_PROTECTION_ENABLED)) {
> > > +        new_cp == DRM_MODE_CONTENT_PROTECTION_ENABLED) ||
> > > +       (old_cp == DRM_MODE_CONTENT_PROTECTION_ENABLED &&
> > > +        new_cp == DRM_MODE_CONTENT_PROTECTION_DESIRED)) {
> > >             if (old_state->hdcp_content_type ==
> > >                             new_state->hdcp_content_type)
> > >                     return;
> > > --
> > > Sean Paul, Software Engineer, Google / Chromium OS
> > >
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