Messages in this thread | | | Subject | Re: [PATCH 3/4] soundwire: SDCA: add helper macro to access controls | From | Bard liao <> | Date | Wed, 26 Aug 2020 09:04:41 +0800 |
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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@linux.intel.com> > Reviewed-by: Guennadi Liakhovetski <guennadi.liakhovetski@linux.intel.com> > Reviewed-by: Kai Vehmanen <kai.vehmanen@linux.intel.com> > Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Acked-by: Bard Liao <yung-chuan.liao@linux.intel.com>
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