[alsa-devel] Rationale for BYTCR defaults in the kernel's bytcr_rt5640 machine driver ?

[Pierre-Louis Bossart]

On 05/01/2018 02:21 PM, Hans de Goede wrote:
> Hi Pierre-Louis,
>
> I'm finally wrapping up my rt5640 jack-detect work, as
> such I'm currently testing speaker + headphones + internal mic +
> headset-mic + jack-detect functionality on the 10 different
> x86 devices with a rt5640 codec which I've gathered.
>
> 2 of them stand out in that they use the BYTCR SoC, but don't
> have the ACPI table for detecting if SSP0 AIF1 or AIF2
> should be used. Currently the driver defaults to AIF2
> in this case.
>
> As the somewhat wildcard-ish DMI quirk for boards where
> the sys_vendor is "Insyde" (which applies to a lot of
> generic designs) shows:
>
>         {
>                 .callback = byt_rt5640_quirk_cb,
>                 .matches = {
>                         DMI_MATCH(DMI_SYS_VENDOR, "Insyde"),
>                 },
>                 .driver_data = (void *)(BYT_RT5640_IN3_MAP |
>                                         BYT_RT5640_MCLK_EN |
>                                         BYT_RT5640_SSP0_AIF1),
>
>         },
>
> AIF1 seems to be a better default both models without
> the ACPI table which I've here, a HP pavilion X2 and a
> Toshiba Click Mini L9W-B need a quirk to use AIF1.
>
> So I was wondering if there was a specific rationale for the
> AIF2 default and if it would not be better to change the default
> to AIF1 (which will unfortunately bring a chance of regressions) ?

yes there was a rationale: all the initial Baytrail designs had 
connections between SSP2-AIF1 and SSP0-AIF2. IIRC this was because there 
was a desire to support 44.1kHz on one SSP and 48kHz on the other.
So when BYT-CR was defined with SSP2 removed, most designs kept the 
existing SSP0-AIF2 link, except of course when they didn't...

I don't have a magic solution here, when the BIOS doesn't provide 
information it's difficult to make an educated guess. If you have 
statistical evidence that more devices without the BIOS information are 
based on AIF2 I don't mind changing it, alternatively we could keep the 
default and when things don't work users can still use a module 
parameter to override the default and get AIF1 to work