[PATCH 2/4] ALSA: hda: intel-nhlt: add intel_nhlt_ssp_mclk_mask()

[Pierre-Louis Bossart]

>>>> +
>>>> +            fmt = (struct nhlt_fmt *)(epnt->config.caps +
>>>> epnt->config.size);
>>>> +            cfg = fmt->fmt_config;
>>>> +
>>>> +            /*
>>>> +             * In theory all formats should use the same MCLK but it
>>>> doesn't hurt to
>>>> +             * double-check that the configuration is consistent
>>>> +             */
>>>> +            for (j = 0; j < fmt->fmt_count; j++) {
>>>> +                u32 *blob;
>>>> +                int mdivc_offset;
>>>> +
>>>> +                if (cfg->config.size >= SSP_BLOB_V1_0_SIZE) {
>>>> +                    blob = (u32 *)cfg->config.caps;
>>>> +
>>>> +                    if (blob[1] == SSP_BLOB_VER_2_0)
>>>> +                        mdivc_offset = SSP_BLOB_V2_0_MDIVC_OFFSET;
>>>> +                    else if (blob[1] == SSP_BLOB_VER_1_5)
>>>> +                        mdivc_offset = SSP_BLOB_V1_5_MDIVC_OFFSET;
>>>> +                    else
>>>> +                        mdivc_offset = SSP_BLOB_V1_0_MDIVC_OFFSET;
>>>> +
>>>> +                    mclk_mask |=  blob[mdivc_offset] & GENMASK(1, 0);
> 
> One more thing, where does this GENMASK come from, as far as I can tell
> HW specifies and FW uses one bit field to signal that MCLK is enabled?
> (mdivc is simply a value written to HW register to configure it).

There are two MCLK signals, that's the point of this patch. We need to
find which one is used. Platforms typically use MCLK0 except when they
don't..

BIT(0) set in mdivc enables MCLK0
BIT(1) set in mdivc enabled MCLK1

see
https://github.com/thesofproject/sof/blob/44a5200c87625588f0028aa08d560e68f2b8dc82/src/drivers/intel/ssp/mn.c#L150

>>>> +                }
>>>> +
>>>> +                cfg = (struct nhlt_fmt_cfg *)(cfg->config.caps +
>>>> cfg->config.size);
>>>> +            }
>>>> +        }
>>>> +        epnt = (struct nhlt_endpoint *)((u8 *)epnt + epnt->length);
>>>> +    }
>>>> +
>>>> +    return mclk_mask;
>>>
>>> Although I understand that it is relegated to the caller, but if both
>>> mclk being set is considered an error maybe add some kind of check here
>>> instead and free callers from having to remember about it?
>>>
>>> if (hweight_long(mclk_mask) != 1)
>>>      return -EINVAL;
>>>
>>> return mclk_mask;
>>
>> I went back and forth multiple times on this one. I can't figure out if
>> this would be a bug or a feature, it could be e.g. a test capability and
>> it's supported in hardware. I decided to make the decision in the caller
>> rather than a lower level in the library.
>>
>> If the tools used to generate NHLT don't support this multi-MCLK mode
>> then we could indeed move the test here.
>>
> 
> Considering comment I added above I've asked Czarek to also check this
> series. I'm not sure it even makes sense to name the field "_mask" when
> it is one bit...

it's two bits, see above.