Re: [PATCH 3/4] soundwire: SDCA: add helper macro to access controls

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On 8/26/2020 1:16 AM, Pierre-Louis Bossart wrote:
The upcoming SDCA (SoundWire Device Class Audio) specification defines
a hierarchical encoding to interface with Class-defined capabilities.

The specification is not yet accessible to the general public but this
information is released with explicit permission from the MIPI Board
to avoid delays with SDCA support on Linux platforms.

A block of 64 MBytes of register addresses are allocated to SDCA
controls, starting at address 0x40000000. The 26 LSBs which identify
individual controls are set based on the following variables:

- Function Number. An SCDA device can be split in up to 8 independent
   Functions. Each of these Functions is described in the SDCA
   specification, e.g. Smart Amplifier, Smart Microphone, Simple
   Microphone, Jack codec, HID, etc.

- Entity Number.  Within each Function,  an Entity is  an identifiable
   block.  Up   to  127  Entities   are  connected  in   a  pre-defined
   graph  (similar to  USB), with  Entity0 reserved  for Function-level
   configurations.  In  contrast  to  USB, the  SDCA  spec  pre-defines
   Function Types, topologies, and allowed  options, i.e. the degree of
   freedom  is not  unlimited to  limit  the possibility  of errors  in
   descriptors leading to software quirks.

- Control Selector. Within each Entity, the SDCA specification defines
   48 controls such as Mute, Gain, AGC, etc, and 16 implementation
   defined ones. Some Control Selectors might be used for low-level
   platform setup, and other exposed to applications and users. Note
   that the same Control Selector capability, e.g. Latency control,
   might be located at different offsets in different entities, the
   Control Selector mapping is Entity-specific.

- Control Number. Some Control Selectors allow channel-specific values
   to be set, with up to 64 channels allowed. This is mostly used for
   volume control.

- Current/Next values. Some Control Selectors are
   'Dual-Ranked'. Software may either update the Current value directly
   for immediate effect. Alternatively, software may write into the
   'Next' values and update the SoundWire 1.2 'Commit Groups' register
   to copy 'Next' values into 'Current' ones in a synchronized
   manner. This is different from bank switching which is typically
   used to change the bus configuration only.

- MBQ. the Multi-Byte Quantity bit is used to provide atomic updates
   when accessing more that one byte, for example a 16-bit volume
   control would be updated consistently, the intermediate values
   mixing old MSB with new LSB are not applied.

These 6 parameters are used to build a 32-bit address to access the
desired Controls. Because of address range, paging is required, but
the most often used parameter values are placed in the lower 16 bits
of the address. This helps to keep the paging registers constant while
updating Controls for a specific Device/Function.

Reviewed-by: Rander Wang <rander.wang@xxxxxxxxxxxxxxx>
Reviewed-by: Guennadi Liakhovetski <guennadi.liakhovetski@xxxxxxxxxxxxxxx>
Reviewed-by: Kai Vehmanen <kai.vehmanen@xxxxxxxxxxxxxxx>
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@xxxxxxxxxxxxxxx>

Acked-by: Bard Liao <yung-chuan.liao@xxxxxxxxxxxxxxx>





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