Daniel Mack wrote:
we're hunting a weird bug on PXA3xx/ssp based audio devices which causes the playback channels to be swapped when the capture stream is started at the same time. Content for the left channel appears on the right and vice versa, in approximately 50% of all test runs
IIRC there was some other CPU where it was tried to program a generic serial output to handle I²S data. The same symptoms appeared because it was not possible to synchronize the start of the L/R signal to the start of the DMA.
Apparently, the starting of the capture stream affects the L/R synchronization of the playback stream.
Does starting playback first work?
I guess this is some sort of a race condition in the stream startup, and suspected sound/soc/pxa/pxa-ssp.c to lack some locking, so I added a spinlock around all register read-modify-write cycles. But that doesn't seem to be the reason.
I'd guess this is a race in the programming of the L/R clock signals; try putting a lock/mutex about all the stream initialization code, and maybe adding some delay.
Regards, Clemens