On 04-11-20, 01:22, Bard Liao wrote: > From: Pierre-Louis Bossart <pierre-louis.bossart@xxxxxxxxxxxxxxx> > > The SoundWire 1.1 specification only allowed for reads and writes of > bytes. The SoundWire 1.2 specification adds a new capability to > transfer "Multi-Byte Quantities" (MBQ) across the bus. The transfers > still happens one-byte-at-a-time, but the update is atomic. > > For example when writing a 16-bit volume, the first byte transferred > is only taken into account when the second byte is successfully > transferred. > > The mechanism is symmetrical for read and writes: > - On a read, the address of the last byte to be read is modified by > setting the MBQ bit > - On a write, the address of all but the last byte to be written are > modified by setting the MBQ bit. The address for the last byte relies > on the MBQ bit being cleared. > > The current definitions for MBQ-based controls in the SDCA draft > standard are limited to 16 bits for volumes, so for now this is the > only supported format. An update will be provided if and when support > for 24-bit and 32-bit values is specified by the SDCA standard. > > One possible objection is that this code could have been handled with > regmap-sdw.c. However this is a new spec addition not handled by every > SoundWire 1.1 and non-SDCA device, so there's no reason to load code > that will never be used. > > Also in practice it's extremely unlikely that CONFIG_REGMAP would not > be selected with CONFIG_REGMAP_MBQ selected. However there's no > functional dependency between the two modules so they can be selected > separately. Reviewed-by: Vinod Koul <vkoul@xxxxxxxxxx> -- ~Vinod
