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

[Anshuman Gupta <anshuman.gupta@intel.com>]

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 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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