Re: [PATCH] media: em28xx: fix silent audio capture on EM2860/TVP5150 reference design

[David Wood <d01.devel@gmail.com>]

On Sun, 13 Sep 2026 23:10:13 +0200, Mauro Carvalho Chehab wrote:

> Instead of touching the reference design, and except if you have the
> real em2861 reference card (unlikely unless you're a manufacturer or
> if some manufacturer donated one to you), you need to create a
> board-specific entry with the brand name used on it, and use
> card=<number>.

Agreed. It is a retail StarTech.com SVID2USB23. v2 adds a board entry
for it and leaves the reference design entry alone.

Since the USB ID is the generic eb1a:5051, v2 identifies the board by
EEPROM hash (0x11b79572), the way em28xx_eeprom_hash[] already does for
other boards with shared IDs, with a lookup in em28xx_card_setup() for
devices that arrive as the reference design. Boards that do not match a
hash keep the reference design entry exactly as before, with no extra
log output. card=114 also works.

> It may also mean that the AC97 chip - either emp202 or a different
> model - is wired on a non-standard way. Those chips have multiple
> inputs that are wired on different ways depending on the board.

It is an EMP202 (vendor ID reads back as such, features 0x6a90) and
Line In is wired as on the reference design: with the record source set
to Line In the capture is clean line level. The only thing missing is
that nothing ever programs the ADC record source, because audio on this
board leaves over a USB Audio Class endpoint fed by the EMP202 ADC
rather than the em28xx vendor path, and .amux only reaches the mixer
volume registers.

> Please use your name instead of "d01".

Done.

> Most boards don't require adjusting aout. On most cases, just amux is
> needed. The above setup also sounds weird: why does it need 3 audio
> lines there?

Two are needed. em28xx_audio_analog_set() only writes AC97_REC_SEL when
EM28XX_AOUT_PCM_IN is set, and EM28XX_AOUT_PCM_LINE is what selects
Line In as the record source, so v2 uses exactly those two, matching the
other entries that set PCM_IN. EM28XX_AOUT_MASTER was only carried over
from the old fallback so the master volume register would keep tracking
the V4L2 volume control; it has no effect on capture on this board, so
it is gone in v2.

Thanks for the review,
David