[PATCH] drm/edid: Refine HDMI VSDB detect

[Lee, Shawn C]

On Monday, December 13, 2021 at 02:36 p.m, Ville Syrjälä wrote:
>On Mon, Dec 13, 2021 at 02:09:33PM +0000, Lee, Shawn C wrote:
>> 
>> On Monday, December 13, 2021 at 12:45 p.m, Ville Syrjälä wrote:
>> >On Mon, Dec 13, 2021 at 12:42:22PM +0000, Lee, Shawn C wrote:
>> >> 
>> >> On Monday, December 13, 2021 8:31 PM, Ville Syrjälä wrote:
>> >> >On Sun, Dec 12, 2021 at 11:33:31PM +0800, Lee Shawn C wrote:
>> >> >> According to CEA-861-F chapter 7.5.4. It says "The VSDB shall contain 
>> >> >> the
>> >> >> 3 bytes of the IEEE OUI as well as any additional payload bytes needed."
>> >> >> Now DRM driver check HDMI OUI but VSDB payload size at least five bytes.
>> >> >> That may caused some HDMI monitors' audio feature can't be enabled.
>> >> >> Because of they only have three bytes payload (OUI only) in VSDB.
>> >> >
>> >> >HDMI 1.4a says
>> >> >"Sinks shall contain an HDMI VSDB minimally containing a 2-byte Source  Physical Address field following the 24-bit identifier. ...
>> >> > The minimum value of N (length) is 5 and the maximum value of N is 31."
>> >> >
>> >> >Do you actually have an EDID that violates that?
>> >> >
>> >> 
>> >> Yes! User report when connect to HDMI port on Acer V226HQL. Audio is not working.
>> >> But windows system did not have the same problem. We found its VSDB just have 3 bytes
>> >> payload (OUI). Then we share this patch to user then they report audio works properly
>> >> with this patch.
>> >
>> >Hrm. This deserves a comment then since it clearly violates the spec.
>> >Also a link to the bug if you have one would be nice to include here.
>> >
>> 
>> Let me create an issue and update monitor's EDID for you reference.
>> But I'm not sure which community is suitable to report this problem.
>> It looks to me should belong to DRM driver https://gitlab.freedesktop.org/drm/misc/-/issues.
>
>That seems fine to me.
>

Here is the link, thanks! https://gitlab.freedesktop.org/drm/misc/-/issues/28

>> Do you have any suggestion? Thanks!
>> 
>> >> 
>> >> Best regards,
>> >> Shawn
>> >> 
>> >> >> 
>> >> >> Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
>> >> >> Cc: Adam Jackson <ajax at redhat.com>
>> >> >> Cc: Dave Airlie <airlied at redhat.com>
>> >> >> Signed-off-by: Lee Shawn C <shawn.c.lee at intel.com>
>> >> >> ---
>> >> >>  drivers/gpu/drm/drm_edid.c | 2 +-
>> >> >>  1 file changed, 1 insertion(+), 1 deletion(-)
>> >> >> 
>> >> >> diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c 
>> >> >> index 12893e7be89b..5aa4a6bf4a13 100644
>> >> >> --- a/drivers/gpu/drm/drm_edid.c
>> >> >> +++ b/drivers/gpu/drm/drm_edid.c
>> >> >> @@ -4205,7 +4205,7 @@ static bool cea_db_is_hdmi_vsdb(const u8 *db)
>> >> >>  	if (cea_db_tag(db) != VENDOR_BLOCK)
>> >> >>  		return false;
>> >> >>  
>> >> >> -	if (cea_db_payload_len(db) < 5)
>> >> >> +	if (cea_db_payload_len(db) < 3)
>> >> >>  		return false;
>> >> >>  
>> >> >>  	return oui(db[3], db[2], db[1]) == HDMI_IEEE_OUI;
>> >> >> --
>> >> >> 2.31.1
>> >> >
>> >> >--
>> >> >Ville Syrjälä
>> >> >Intel
>> >> >
>