[alsa-devel] [PATCH] ASoC: rt1011: export r0 and temperature config

[Cheng-yi Chiang]

On Tue, Oct 8, 2019 at 6:51 PM Mark Brown <broonie at kernel.org> wrote:
>
> On Tue, Oct 08, 2019 at 09:33:24AM +0000, Shuming [范書銘] wrote:
>
> > In chromebook case, the machine driver will get the
> > r0 calibration data and temperature from VPD.
> > Therefore, the codec exports r0 and temperature config API for it.
>
> Why will the machine driver do this?

Hi Mark,
The calibration data (R0 values and temperature) were measured and
written to VPD in the factory. When machine driver initializes sound
card, it reads the value from VPD and uses the exported API to set
calibration value for codec. The purpose is to protect speaker. This
needs to be done before sound card is initialized. If, alternatively,
this process is done in user space through mixer control after the
sound card is initialized, user space may use audio before calibration
is done, and this will allow the possibility to damage speakers.
Hope this clarifies the intention of this patch.
Thanks!