[PATCH] ASoC: max98357a: set channels_max to 4

[Cheng-yi Chiang]

On Wed, Jun 16, 2021 at 12:00 AM Pierre-Louis Bossart
<pierre-louis.bossart at linux.intel.com> wrote:
>
>
>
> On 6/15/21 10:47 AM, Cheng-yi Chiang wrote:
> > Hi Tzung-Bi,
> >
> > On a platform, the four max98357a amps will be controlled by only one
> > codec device, as GPIO for SD_MODE is shared by all amps and is the
> > only thing to be controlled.
> > In this sense, I think we can treat max98357a DAI as if it supports
> > four channels.
> > I understand that this solution is not scalable, because one can
> > control as many amps as they want.
> > Theoretically, the number of supported channels by this codec device
> > is unlimited.
> > I found that rt1015.c has similar usage.
> > Do you have a better suggestion to support this kind of use case ?
> > Thanks!
>
> please don't top-post...
Hi Pierre-Louis,

I am sorry about that!
>
>
> I don't think it's correct to declare 4-channel support at the
> individual codec DAI level when in practice each device will be provided
> with a TDM mask that selects two slots.

On this platform there is no TDM support, so there were two I2S data lines.

>
> This is confusing device capabilities and TDM link configuration.

I see that in most of the use cases of multiple amps, we should use
codecs and num_codecs of the link.
But in this case we only want one codec to control the only GPIO
shared by 4 max98357a amps
I think we should be able to use 1 max98357 codec and 3 dummy codec to
fulfill this use case.
Not sure if the number of dummy codec would really matter.
With num_codec > 1 we should be able to bypass the channel checking
and just use the channel from CPU DAI.
Thanks for the suggestion.


>
> > On Tue, Jun 1, 2021 at 2:20 PM Tzung-Bi Shih <tzungbi at google.com> wrote:
> >>
> >> On Wed, May 26, 2021 at 11:47 PM Judy Hsiao <judyhsiao at chromium.org> wrote:
> >>> Sets channels_max to 4 to support QUAD channel.
> >>
> >> Could you point out probably the up-to-date MAX98357A datasheet for
> >> 4-channel support?
> >>
> >> On a related note, from the public datasheet I could find[1], "Table
> >> 5" only shows 2 channel's configuration.
> >>
> >> [1]: https://pdf1.alldatasheet.com/datasheet-pdf/view/623796/MAXIM/MAX98357A.html