HDCP Content Type Interface

[Harry Wentland]

On 2019-09-12 10:49 a.m., Ramalingam C wrote:
> On 2019-09-12 at 14:23:05 +0000, Harry Wentland wrote:
>> On 2019-09-12 3:47 a.m., Ramalingam C wrote:
>>> On 2019-09-09 at 15:54:50 +0000, Lakha, Bhawanpreet wrote:
>>>> Hi all,
>>>>
>>>> This is regarding the recent hdcp content type patch that was merged into drm-misc. (https://patchwork.freedesktop.org/patch/320958/?series=57233&rev=11)
>>>>
>>>> There are displays on the market that advertise HDCP 2.2 support and will pass authentication and encryption but will then show a corrupted/blue/black screen (the driver cannot detect this). These displays work with HDCP 1.4 without any issues. Due to the large number of HDCP-supporting devices on the market we might not be able to catch them with a blacklist.
>>>>
>>>> From the user modes perspective, HDCP1.4 and HDCP2.2 Type0 are the same thing. Meaning that this interface doesn't allow us to force the hdcp version. Due to the problems mentioned above we might want to expose the ability for a user to force an HDCP downgrade to a certain level (e.g. 1.4) in case they experience problems.
>>>>
>>>> What are your thoughts? and what would be a good way to deal with it?
>>> Hi,
>>>
>>> As you mentioned, uAPI is designed to be HDCP version agnostic. Kernel
>>> supposed to exercise the highest version of HDCP supported on panel and
>>> platform.
>>>
>>> As we implement the HDCP spec support, if a device is non-compliant with
>>> HDCP spec after completing the HDCP authentication, I dont think we need
>>> to worry about it.
>>>
>>
>> Tell that to our (or your) customers.
>>
>> In this case an enduser might plug in a bad monitor or TV and be unable
>> to play protected content.
>>
>> What if we add a new enum value to the content_type property that says
>> "DRM_MODE_HDCP_CONTENT_TYPE_FORCE_14"?
> "content type" is for defining the stream type. Adding an entry into it
> sounds like polluting it.
> 

For sure

> Separate uAPI for forcing a HDCP version might be need. Or wondering on
> using the sysfs of connector for this dirty job!?
> 

Did a bit more digging...

On other OS we got a monitor quirk for a few displays and also something
similar to a module parameter to force disable HDCP 2.x support.

It looks like there aren't too many quirky receivers so that might be an
acceptable solution. I'm still thinking a connector property might be
useful to force a certain HDCP version but maybe I'm overthinking it.

Harry

> -Ram
>>
>> Harry
>>
>>> In case if you want to track and implement a quirk for it, like not to
>>> project the HDCP2.2 capability, you can use the receiver id of that panel
>>> to track it.
>>>
>>> Thanks,
>>> -Ram
>>>>
>>>>
>>>> Thanks,
>>>>
>>>> Bhawan