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Date:   Wed, 26 Aug 2020 09:04:41 +0800
From:   Bard liao <>
To:     Pierre-Louis Bossart <>,
Cc:     Kai Vehmanen <>,
        Guennadi Liakhovetski <>,,,,
        Ranjani Sridharan <>,
        Hui Wang <>,,,,,,
        Sanyog Kale <>,
        Rander Wang <>
Subject: Re: [PATCH 3/4] soundwire: SDCA: add helper macro to access controls

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 <>
> Reviewed-by: Guennadi Liakhovetski <>
> Reviewed-by: Kai Vehmanen <>
> Signed-off-by: Pierre-Louis Bossart <>

Acked-by: Bard Liao <>

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