linux-kernel - Re: [PATCH v6 4/5] drm/bridge: anx7625: add HDCP support

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Date:   Mon, 29 Mar 2021 14:02:08 -0400
From:   Sean Paul <sean@...rly.run>
To:     Xin Ji <xji@...logixsemi.com>
Cc:     Foss <robert.foss@...aro.org>,
        Nicolas Boichat <drinkcat@...gle.com>,
        Andrzej Hajda <a.hajda@...sung.com>,
        devel@...verdev.osuosl.org,
        Jernej Skrabec <jernej.skrabec@...l.net>,
        Sheng Pan <span@...logixsemi.com>,
        Jonas Karlman <jonas@...boo.se>,
        David Airlie <airlied@...ux.ie>,
        Bernie Liang <bliang@...logixsemi.com>,
        Neil Armstrong <narmstrong@...libre.com>,
        Zhen Li <zhenli@...logixsemi.com>,
        LKML <linux-kernel@...r.kernel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Vasily Khoruzhick <anarsoul@...il.com>,
        Boris Brezillon <boris.brezillon@...labora.com>,
        Torsten Duwe <duwe@....de>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Hsin-Yi Wang <hsinyi@...omium.org>,
        Sam Ravnborg <sam@...nborg.org>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>
Subject: Re: [PATCH v6 4/5] drm/bridge: anx7625: add HDCP support

On Mon, Mar 29, 2021 at 6:27 AM Xin Ji <xji@...logixsemi.com> wrote:
>
> On Thu, Mar 25, 2021 at 02:19:23PM -0400, Sean Paul wrote:
> > On Fri, Mar 19, 2021 at 2:35 AM Xin Ji <xji@...logixsemi.com> wrote:
> > >
> > > Add HDCP feature, enable HDCP function through chip internal key
> > > and downstream's capability.
> > >
> > > Signed-off-by: Xin Ji <xji@...logixsemi.com>
> > > ---

/snip

> > >  static void anx7625_dp_start(struct anx7625_data *ctx)
> > >  {
> > >         int ret;
> > > @@ -643,6 +787,9 @@ static void anx7625_dp_start(struct anx7625_data *ctx)
> > >                 return;
> > >         }
> > >
> > > +       /* HDCP config */
> > > +       anx7625_hdcp_setting(ctx);
> >
> > You should really use the "Content Protection" property to
> > enable/disable HDCP instead of force-enabling it at all times.
> >
> > Sean
> Hi Sean, it's hard to implement "Content Protection" property, we have
> implemented HDCP in firmware, it is not compatible with it. We don't
> have interface to get Downstream Cert.
> Thanks,
> Xin

Hi Xin,
I'm sorry, I don't understand what you mean when you say you don't
have an interface to get Downstream Cert.

The Content Protection property is just a means through which
userspace can turn on and turn off HDCP when it needs. As far as I can
tell, your patch turns on HDCP when the display is enabled and leaves
it on until it is disabled. This is undesirable since it forces HDCP
on the user.

Is it impossible to enable/disable HDCP outside of display
enable/disable on your hardware?

Thanks,

Sean

> >
> > > +
> > >         if (ctx->pdata.is_dpi)
> > >                 ret = anx7625_dpi_config(ctx);
> > >         else

/snip