linux-kernel - Re: [PATCH v1 RFC] video/hdmi: Fix HDMI_VENDOR_INFOFRAME

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Message-ID: <CAFBinCC6RRiN0=XYNw464omzjHrRcNZn39i3_Ztfq6M2xMpgRw@mail.gmail.com>
Date:   Tue, 14 Feb 2023 22:26:24 +0100
From:   Martin Blumenstingl <martin.blumenstingl@...glemail.com>
To:     Ville Syrjälä <ville.syrjala@...ux.intel.com>
Cc:     dri-devel@...ts.freedesktop.org, Helge Deller <deller@....de>,
        linux-fbdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        Hans Verkuil <hans.verkuil@...co.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Bernard Zhao <bernard@...o.com>
Subject: Re: [PATCH v1 RFC] video/hdmi: Fix HDMI_VENDOR_INFOFRAME_SIZE

On Mon, Feb 13, 2023 at 12:11 PM Ville Syrjälä
<ville.syrjala@...ux.intel.com> wrote:
[...]
> > One could use HDMI_VENDOR_INFOFRAME_SIZE with this as well:
> >   u8 buffer[HDMI_INFOFRAME_SIZE(VENDOR)];
> > But it would only result in an 8 byte wide buffer.
> > Nobody uses it like this yet.
>
> Not sure that would make any sense since a vendor
> specific infoframe has no defined size until you
> figure out which vendor defined it (via the OUI).
My understanding is that all of the existing HDMI vendor infoframe
code is built for HDMI_IEEE_OUI.

> I suppose the current value of 4 is also a bit nonsense
> as well then, becasue that is a legal value for the
> HDMI 1.4 vendor specific infoframe, but might not be
> valid for any other infoframe.
>
> We should perhaps just get rid of HDMI_VENDOR_INFOFRAME_SIZE
> entirely.
My thought was to make it the correct size for
drm_hdmi_vendor_infoframe_from_display_mode(). Then developers using
this "common" vendor infoframe don't have to worry much.
If there's another vendor infoframe implementation (which I'm not
aware of, but it may exist - since as you point out: it's vendor
specific) then the driver code shouldn't use
drm_hdmi_vendor_infoframe_from_display_mode() but rather implement
something custom. At that point the person implementing that will also
need to know their specific infoframe maximum size.


Best regards,
Martin