linux-kernel - RE: [PATCH v2 1/2] dt-bindings: drm/bridge: MHDP8546 bridge binding changes for HDCP

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Message-ID: <DM5PR07MB3196C4564D51182A8068DD81C1929@DM5PR07MB3196.namprd07.prod.outlook.com>
Date:   Tue, 9 Mar 2021 08:02:32 +0000
From:   Parshuram Raju Thombare <pthombar@...ence.com>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>
CC:     "robert.foss@...aro.org" <robert.foss@...aro.org>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "airlied@...ux.ie" <airlied@...ux.ie>,
        "daniel@...ll.ch" <daniel@...ll.ch>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "a.hajda@...sung.com" <a.hajda@...sung.com>,
        "narmstrong@...libre.com" <narmstrong@...libre.com>,
        "nikhil.nd@...com" <nikhil.nd@...com>,
        "kishon@...com" <kishon@...com>,
        Swapnil Kashinath Jakhade <sjakhade@...ence.com>,
        Milind Parab <mparab@...ence.com>
Subject: RE: [PATCH v2 1/2] dt-bindings: drm/bridge: MHDP8546 bridge binding
 changes for HDCP

>> >>> Is this a property of the hardware, that is, are there multiple versions
>> >>> of this IP core covered by the same compatible string that support HDCP
>> >>> 1.4 only, DHCP 2.2 only or both ? Or is it a way to select what a given
>> >>> system will offer ?[]
>> >>
>> >> MHDP hardware supports both HDCP 2.2 and 1.4. So, this is a way
>> >> to select the version of HDCP, system wish to support.
>> >
>> > Then I'm not sure this qualifies as a DT property, which should describe
>> > the system, not configure it. A way for userspace to configure this
>> > would be better.
>>
>> Since this is for source device, I am not sure how useful it is to allow
>> user to change HDCP version supported. I think doing it in DTS
>> gives more control over HDCP to system designer/integrator.
>
>But how would they do so ? What would be the rationale for selecting a
>particular version in DT ?
>
>I'm not thinking about giving control of this parameter to the end-user,
>but in the context of an embedded system, it may be useful to select
>which HDCP versions to offer based on different constraints at runtime.
>This really seems like a system configuration parameter to me, not a
>system description.

Ok, we can remove this parameter from DTS and let driver attempt both
HDCP 2.2 and HDCP 1.4 in the same sequence so that HDCP version is
selected based on sink capabilities. But then user space application will
not have information about the HDCP version with which content will be
protected. I suppose most UHD 4k content would need HDCP 2.2.
So, forcing HDCP version in DTS was the easiest way.

Regards,
Parshuram Thombare