On Fri, Jul 12, 2019 at 02:39:05PM +0300, Pekka Paalanen wrote:
> On Thu, 11 Jul 2019 10:18:22 -0400
> Sean Paul <s...@poorly.run> wrote:
>
> > On Mon, Jul 08, 2019 at 04:51:11PM +0530, Ramalingam C wrote:
> > > This patch adds a DRM ENUM property to the selected connectors.
> > > This property is used for mentioning the protected content's type
> > > from userspace to kernel HDCP authentication.
> > >
> > > Type of the stream is decided by the protected content providers.
> > > Type 0 content can be rendered on any HDCP protected display wires.
> > > But Type 1 content can be rendered only on HDCP2.2 protected paths.
> > >
> > > So when a userspace sets this property to Type 1 and starts the HDCP
> > > enable, kernel will honour it only if HDCP2.2 authentication is through
> > > for type 1. Else HDCP enable will be failed.
> > >
> > > Need ACK for this new conenctor property from userspace consumer.
>
> ...
>
> > > diff --git a/drivers/gpu/drm/drm_connector.c
> > > b/drivers/gpu/drm/drm_connector.c
> > > index 068d4b05f1be..732f6645643d 100644
> > > --- a/drivers/gpu/drm/drm_connector.c
> > > +++ b/drivers/gpu/drm/drm_connector.c
> > > @@ -952,6 +952,45 @@ static const struct drm_prop_enum_list
> > > hdmi_colorspaces[] = {
> > > * is no longer protected and userspace should take appropriate
> > > action
> > > * (whatever that might be).
> > > *
> > > + * HDCP Content Type:
> > > + * This Enum property is used by the userspace to declare the
> > > content type
> > > + * of the display stream, to kernel. Here display stream stands
> > > for any
> > > + * display content that userspace intended to render with HDCP
> > > encryption.
> > > + *
> > > + * Content Type of a stream is decided by the owner of the stream,
> > > as
> > > + * "HDCP Type0" or "HDCP Type1".
> > > + *
> > > + * The value of the property can be one the below:
> > > + * - "HDCP Type0": DRM_MODE_HDCP_CONTENT_TYPE0 = 0
> > > + * - "HDCP Type1": DRM_MODE_HDCP_CONTENT_TYPE1 = 1
> > > + *
> > > + * When kernel starts the HDCP authentication upon the "DESIRED"
> > > state of
> > > + * the "Content Protection", it refers the "HDCP Content Type"
> > > property
> > > + * state. And perform the HDCP authentication with the display
> > > sink for
> > > + * the content type mentioned by "HDCP Content Type".
> > > + *
> > > + * Stream classified as HDCP Type0 can be transmitted on a link
> > > which is
> > > + * encrypted with HDCP 1.4 or higher versions of HDCP(i.e HDCP2.2
> > > + * and more).
> > > + *
> > > + * Streams classified as HDCP Type1 can be transmitted on a link
> > > which is
> > > + * encrypted only with HDCP 2.2. In future, HDCP versions >2.2
> > > also might
> > > + * support Type1 based on their spec.
> > > + *
> > > + * HDCP2.2 authentication protocol itself takes the "Content Type"
> > > as a
> > > + * parameter, which is a input for the DP HDCP2.2 encryption algo.
> > > + *
> > > + * Note that the HDCP Content Type property is introduced at HDCP
> > > 2.2, and
> > > + * defaults to type 0. It is only exposed by drivers supporting
> > > HDCP 2.2.
> > > + * Based on how next versions of HDCP specs are defined content
> > > Type could
> > > + * be used for higher versions too.
> > > + *
> > > + * If content type is changed when "Content Protection" is not
> > > UNDESIRED,
> > > + * then kernel will disable the HDCP and re-enable with new type
> > > in the
> > > + * same atomic commit. And when "Content Protection" is ENABLED,
> > > it means
> > > + * that link is HDCP authenticated and encrypted, for the
> > > transmission of
> > > + * the Type of stream mentioned at "HDCP Content Type".
> > > + *
> > > * HDR_OUTPUT_METADATA:
> > > * Connector property to enable userspace to send HDR Metadata to
> > > * driver. This metadata is based on the composition and blending
> >
> > Do we actually need an entirely new property? Can't we just add a new
> > entry to the existing Content Protection property which is "Desired Type1"
> > or
> > similar? The kernel will then either attempt 2.2 auth or it will ignore it
> > the
> > request if it's not supported.
>
> Hi,
>
> IMHO the existing "Content Protection" property is already complicated
> enough that one should not add anything new to it.
>
> If you added "desired-type-1", the readback of it would become
> ambiguous if it was "ENABLED", userspace would not know if the value
> written was "DESIRED" or "desired-type-1". Sure, it's not a problem
> when a display server knows what it just wrote into it, but shouldn't
> we try to keep KMS state readable as well, if for nothing but debugging?
Yeah, that's a fair point, it would also create a problem if the HDCP version
was somehow downgraded between u/s polling the property.
>
> I think using the same property for communicating in both directions
> between the kernel and userspace (value can be set by both userspace and
> kernel at times) was a mistake to begin with.
We can agree on that. I figured that since we already had the subpar UAPI, we're
stuck with it anyways.
In light of the above though, I agree a new property makes sense to me.
Sean
> It has already caused
> long discussions on what the readback actually should reflect and
> whether there are races for a given userspace implementation.
>
>
> Thanks,
> pq
--
Sean Paul, Software Engineer, Google / Chromium OS
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