Re: [PATCH] TDA1997x: enable EDID support

Tim Harvey
2021-06-07T15:49:50Z

On Mon, Jun 7, 2021 at 4:56 AM Krzysztof Hałasa <khalasa@piap.pl> wrote:
>
> Hi Hans,
>
> Hans Verkuil <hverkuil@xs4all.nl> writes:
>
> >> Without this patch, the TDA19971 chip's EDID is inactive.
> >
> > Was this wrong from the very beginning? How can this ever have been tested
> > without an EDID?
>
> It seems so. I suspect it might have worked in tests because this
> register isn't cleared on reboot. I.e., setting it once after power up
> makes it work to the next power up.
> Or, maybe, the HDMI signal source didn't need EDID.
>

Krzysztof,

Most likely it was that the HDMI signal source I tested with didn't
need EDID. I primarily used a V-SG4K HMDI signal generator in my
testing and development of the driver
(http://www.marshall-usa.com/monitors/model/V-SG4K-HDI.php) which
definitely doesn't need it. Other devices I tested with were another
Gateworks board with HDMI out (which also didn't need EDID) and
occasionally a 1st gen Google Chromecast and Amazon Fire stick (which
I'm not sure about).

> I'm looking at the previous version of this driver from Gateworks and it
> contains:
>
> /* Configure EDID
> *
> * EDID_ENABLE bits:
> * 7 - nack_off
> * 6 - edid_only
> * 1 - edid_b_en
> * 0 - edid_a_en
> */
> reg = io_read(REG_EDID_ENABLE);
> if (!tda1997x->internal_edid)
> reg &= ~0x83; /* EDID Nack ON */
> else
> reg |= 0x83; /* EDID Nack OFF */
> io_write(REG_EDID_ENABLE, reg);
>
> Not sure what the "non-internal" EDID could be - a separate I2C EEPROM
> chip? I'm using this on Gateworks' GW54xx boards and I can't see any
> such EEPROM in the vicinity of the TDA19971, but I don't know how it is
> wired - perhaps Tim has some idea?

Not sure where the source above is from (this was all so long ago) but
my guess is that 'internal_edid' meant an EDID had been provided via
software and the else case meant there was no EDID available. There is
no support on that chip for an external EEPROM.

Tim