Re: [PATCH v1 RFC] video/hdmi: Fix HDMI_VENDOR_INFOFRAME_SIZE

[Martin Blumenstingl]

On Mon, Feb 13, 2023 at 12:11 PM Ville Syrjälä
<ville.syrjala@xxxxxxxxxxxxxxx> 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