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From:   =?utf-8?Q?Krzysztof_Ha=C5=82asa?= <khalasa@piap.pl>
To:     Tim Harvey <tharvey@gateworks.com>
Cc:     Hans Verkuil <hverkuil@xs4all.nl>,
        Mauro Carvalho Chehab <mchehab@kernel.org>,
        linux-media <linux-media@vger.kernel.org>,
        lkml <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] TDA1997x: enable EDID support
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Date:   Tue, 08 Jun 2021 06:54:57 +0200
In-Reply-To: <CAJ+vNU0E_0pB-1T+VpdmjJNVirAwCUNjKVbEV4wEbqHOzURj_A@mail.gmail.com>
        (Tim Harvey's message of "Mon, 7 Jun 2021 08:48:19 -0700")
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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 =3D io_read(REG_EDID_ENABLE);
>>      if (!tda1997x->internal_edid)
>>          reg &=3D ~0x83; /* EDID Nack ON */
>>      else
>>          reg |=3D 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 &=3D ~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 =3D 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.
--=20
Krzysztof Ha=C5=82asa

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