Re: [PATCH] TDA1997x: enable EDID support

Hans Verkuil
2021-06-08T07:27:39Z

Hi Krzysztof,

On 08/06/2021 06:54, Krzysztof Hałasa wrote:
> Tim,
>
> Tim Harvey <tharvey@gateworks.com> writes:
>
>>> 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 where the source above is from (this was all so long ago) but
>
> That's your gateworks_fslc_3.14_1.0.x_ga branch (3.14 is the kernel and
> 1.0.x_ga is IIRC some Freescale versioning) :-)
>
>> 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.
>
> Right. I guess the else meant it was available and &= ~83 meant no
> EDID... Anyway one could simply drop a 24c02 or a similar chip directly
> to SDA/SCL HDMI lines, that's what the monitor makers had been doing for
> a long time. Then, I guess, you would need the internal_edid = 0
> (otherwise the TDA chip would be fighting the EEPROM on the SDA line).
> Not that I know of any such design using this driver, I guess we can
> safely skip this part.
>

OK, I think the history is clear. Can you post a v2 with a Fixes tag and
comment a bit on why this was not caught before?

Regards,

Hans