Re: [PATCH v5 1/4] ACPI: NHLT: Reintroduce types the table consists of

[Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>]

On 3/4/24 14:34, Cezary Rojewski wrote:
> On 2024-03-04 9:22 PM, Pierre-Louis Bossart wrote:
>> On 3/4/24 13:49, Andy Shevchenko wrote:
>>> On Mon, Mar 04, 2024 at 10:57:39AM -0600, Pierre-Louis Bossart wrote:
>>>>> +/* Values for link_type field above */
>>>>> +
>>>>> +#define ACPI_NHLT_LINKTYPE_HDA            0
>>>>> +#define ACPI_NHLT_LINKTYPE_DSP            1
>>>>> +#define ACPI_NHLT_LINKTYPE_PDM            2
>>>>> +#define ACPI_NHLT_LINKTYPE_SSP            3
>>>>> +#define ACPI_NHLT_LINKTYPE_SLIMBUS        4
>>>>> +#define ACPI_NHLT_LINKTYPE_SDW            5
>>>>> +#define ACPI_NHLT_LINKTYPE_UAOL            6
>>>>
>>>> More than half of those values are not used. Is there really any
>>>> benefit
>>>> in exposing them?
>>>
>>> Sometimes a code is the (only) documentation. Since it's a global
>>> header and
>>> part of ACPICA we probably better to expose all bits that are defined.
>>
>> NHLT is an Intel-only solution - no other company uses it.
>> Intel does not have any designs where SlimBus is productized.
>>
>> I fail to see the wisdom of exposing a non-existent option with
>> LINKTYPE_SLIMBUS. It's not because this case was listed in a document
>> that we have to add the information verbatim in a open-source header.
>>
>> Likewise for SoundWire we do NOT use NHLT at all...
>>
>> Options 4 and 5 are completely irrelevant. 0 and 1 most likely as well.
> 
> Hello,
> 
> How relevant or not given field is in LINKTYPE enumeration is..
> irrelevant. Those values are reserved since the dawn of the table.
> Renaming those with range of RESERVED_X(s) is hardly an alternative. On
> top of that, specs which have been publicly shared since 2016 _do_ list
> the non-I2S/PDW constants when describing LINKTYPE.

I maintain that all those values, while spec-defined, should be treated
as not supported. It's not unusual in engineering to change directions
and back-annotate, demote or cleanup initial designs. Change is the only
constant.