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

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Message-ID: <m3eeddhora.fsf@t19.piap.pl>
Date:   Mon, 07 Jun 2021 13:56:25 +0200
From:   Krzysztof Hałasa <khalasa@...p.pl>
To:     Hans Verkuil <hverkuil@...all.nl>
Cc:     Tim Harvey <tharvey@...eworks.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        linux-media@...r.kernel.org, lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] TDA1997x: enable EDID support

Hi Hans,

Hans Verkuil <hverkuil@...all.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.

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?
-- 
Krzysztof Hałasa

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