Jerzy Kasenberg 8b37aa1579 nrf5x: Fix DMA access ...

There were two problems:
- dma_running flag could be checked in USB interrupt (not set yet) then higher priority
  interrupt could start transfer, check dma_running (not set yet) set it to true start
  DMA; then when USB interrupt continues it starts another DMA that is not allowed
- when DMA is started some registers can't be safely accessed, read can yield invalid
  values (SIZE.EPOUT, SIZE.EPISO)
  current implementation could start DMA for one OUT endpoint then check that another
  endpoint also has data and while DMA was not started right away, SIZE.EPOUT was copied
  already to MAXCNT register. Later on when DMA was started not all data was read from
  endpoint due to incorrect DMA size previously set.

To prevent both cases dma_running is changed in atomic way.
Only code that actually set this value to true starts DMA, code that tried and
had dma_running flag already set simply defers DMA start to USB task.
This eliminates also need to have mutex that was there to limit access to dma_running flag
to one task only.
transfer also now has started flag that is set only after dcd_edpt_xfer() sets up total_len
and actua_len. Previously USB interrupt was disabled when total_len and actual_len were
setup to prevent race condition when data arrived to ednpoint before transfer was setup
was finished.

2022-06-02 17:23:35 +02:00

..

dcd_nrf5x.c

nrf5x: Fix DMA access

2022-06-02 17:23:35 +02:00