Re: [EXTERNAL] Re: [PATCH v9] ASoc: tas2783: Add tas2783 codec driver
From: Pierre-Louis Bossart
Date: Mon Feb 26 2024 - 11:06:18 EST
On 2/23/24 12:20 PM, Mark Brown wrote:
On Fri, Feb 23, 2024 at 10:12:49AM +0000, Ding, Shenghao wrote:
Hi Pierre-Louis
In the SoundWire spec, the unique_id is *LINK SPECIFIC*, and only used at
the bus level within the context of a link to help avoid enumeration
conflicts
If you are using the unique_id as a SYSTEM-UNIQUE value to lookup EFI
data, this is a TI-specific requirement that needs to be documented.
That also means you need to double-check for errors so make sure there
are no board configurations where the same unique_id is used in multiple
links, or by devices other than tas2783.
This code only covers the tas2783s sitting in the same bus link. As to cases of the
different SWD links, customer will be required to have the secondary development
on current code. I'm sure my customers have much knowledge to handle this.
PC OEMs don't usually have a Linux team capable of handling this sort of
low-level plumbing, so the burden of this "secondary development" will
come back at you...
As Pierre says I think we really should have some sort of defensive
programming here, even if you're going to leave multi-link systems to
future work people will still have older versions in distributions or
whtaever. While I'm not sure the consequences of getting things wrong
are likely to be that bad (I'm expecting bad quality audio) it's also
going to be kind of hard to figure out if we just silently pick the
wrong calibration, especially if it's actually a valid calibration for
another device in the system. Other vendors (eg, Cirrus) seem to have
figured out a scheme here?
Leaving multi-link aside has to be seen as as temporary step, there are
a number of electrical issues that will prevent more than 4 amps to be
placed on the same link. And indeed this "secondary development" has to
be backwards compatible with initial calibration schemes.