Re: [BUG] ASoC: tas2783-sdw: every amp on the link selects the same channel, so a two-amp board plays mono

[Andrey Golovko]

On 8/6/26 22:30, Pierre-Louis Bossart wrote:

> Maybe the mapping is implicit and defined by the Unique Number
>
> I am not sure though how that Unique Number maps to the -1 and -2 suffix
>
> sdw:0:1:0102:0000:01:8   TAS2783, device_number 3, slave-tas2783
> sdw:0:1:0102:0000:01:b   TAS2783, device_number 2, slave-tas2783
>
> which one is left and which one is right?

Measured on a second HN7306EAC (I'm the andrey.golovko in Cc - same
machine, same two amps at unique ID 0x8/0xB): 0x8 is the left speaker,
0xB the right. Confirmed by muting each amp's volume control in turn,
and by speaker-test with a per-amp one-channel mask applied: channel 1
comes out of the physically left speaker only, channel 2 out of the
right only. That matches Robin's amp 1 = left, amp 2 = right.

The Unique Number to -1/-2 suffix mapping is not implicit - it is
hardcoded in the kernel's machine descriptor. amd-acp70-acpi-match.c
has, for exactly this platform (rt721_l1u0_tas2783x2_l1u8b_adr):

  .adr = 0x0001380102000001  ->  .name_prefix = "tas2783-1", spk_l_endpoint
  .adr = 0x00013B0102000001  ->  .name_prefix = "tas2783-2", spk_r_endpoint

where spk_l_endpoint/spk_r_endpoint are aggregated endpoints with
group_position 0 and 1. So a channel-to-peripheral binding does exist
in the tree, keyed off the _ADR unique ID and complete with a
left/right position - it is just not plumbed into playback port
allocation: nothing turns group_position into a per-peripheral mask or
offset. device_number (2/3 here) is attach order and indeed cannot be
relied on; the unique ID via the match table can.

For cross-reference: the same mono issue on this machine was reported
in July by Antoine Monnet (added to Cc), with an inline patch of the
same shape as Robin's - per-amp one-channel mask derived from the
name_prefix suffix:

  https://lore.kernel.org/all/778f017a-e1c2-4ab6-9968-6e4c6285180b@xxxxxxxxxxxx/

I have been running it since late July with correct physical L/R on my
unit (Tested-by in that thread). Robin's finding that the mask value
is ignored and only its weight matters applies to that patch equally:
it works because the DAI-link codec order follows the adr_d table
order above, which happens to match the speakers. Given that the
descriptor already carries group_position per unique ID, deriving the
assignment from that rather than from parsing the name_prefix suffix
looks like the natural fix, and it would keep working if enumeration
order ever changed.

Thanks,
Andrey