linux-kernel - Re: [PATCH] TDA1997x: enable EDID support

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Message-ID: <m3k0n57y72.fsf@t19.piap.pl>
Date:   Tue, 08 Jun 2021 06:54:57 +0200
From:   Krzysztof Hałasa <khalasa@...p.pl>
To:     Tim Harvey <tharvey@...eworks.com>
Cc:     Hans Verkuil <hverkuil@...all.nl>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        linux-media <linux-media@...r.kernel.org>,
        lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] TDA1997x: enable EDID support

Tim,

Tim Harvey <tharvey@...eworks.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.
-- 
Krzysztof Hałasa

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