On 12/1/22 08:08, Richard Fitzgerald wrote:
Writing zero to the page registers after each message transaction can add up to a lot of overhead for codecs that need to transfer large amount of data - for example a firmware download.
There's no spec reason I can see for this zeroing. The page registers are only used for a paged address. The bus code uses a non-paged address for registers in page 0. It always writes the page registers at the start of a paged transaction.
If this zeroing was a workaround for anything, let me know and I will re-implement the zeroing as a quirk that can be enabled only when it is necessary.
It's a feature, not a bug :-)
The page registers have to be zeroed out so that any bus-management command hits the page0 instead of using a value that was set by codec driver for vendor-specific configurations.
The implementation is far from optimal though, and indeed if we have long transactions that are not interrupted by anything else we could avoid resetting the page registers.
I tried to implement a 'lazy approach' some time back, but at the time I didn't see any benefits due to the limited number of configurations.
I can't remember where the code is, but the initial enhancement was listed here: https://github.com/thesofproject/linux/issues/2881
Richard Fitzgerald (2): soundwire: bus: Don't zero page registers after every transaction soundwire: bus: Remove unused reset_page_addr() callback
drivers/soundwire/bus.c | 23 ----------------------- drivers/soundwire/cadence_master.c | 14 -------------- drivers/soundwire/cadence_master.h | 3 --- drivers/soundwire/intel_auxdevice.c | 1 - include/linux/soundwire/sdw.h | 3 --- 5 files changed, 44 deletions(-)