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

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Message-ID: <YEaMTbJ7Wx7otX2k@pendragon.ideasonboard.com>
Date:   Mon, 8 Mar 2021 22:42:53 +0200
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Parshuram Raju Thombare <pthombar@...ence.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

Hi Parshuram,

On Tue, Mar 02, 2021 at 12:53:50PM +0000, Parshuram Raju Thombare wrote:
> Hi Laurent,
> 
> >>> 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.

-- 
Regards,

Laurent Pinchart