While bringing up EHCI (8-CURRENT, new USB stack) on ARM machine we have found cache-related problem in the USB stack.
The usb_pc_cpu_flush() and usb_pc_cpu_invalidate() functions are used to flush/invalidate CPU caches in various places in USB code. Internally, the functions are implemented using bus_dmamap_sync(). In our case, on ARM machine, flags passed to the bus_dmamap_sync() function did not correspond with requested operation. We have fixed the problem by changing flags passed to the bus_dmamap_sync() function (see attached patch). My question is about general idea of bus_dma usage for cache operations. In my opinion we should not rely on bus_dmamap_sync() behaviour as this function may do different things on different architectures. This not always works as expected, which is clearly visible in our case. Better solution is to use cpu-specific functions implementing cache operations. Please comment on why CPU-specific functions are not used... Patch fixing our problem: diff --git a/sys/dev/usb/usb_busdma.c b/sys/dev/usb/usb_busdma.c index 3d6a5be..69a6fff 100644 --- a/sys/dev/usb/usb_busdma.c +++ b/sys/dev/usb/usb_busdma.c @@ -658,8 +658,7 @@ usb_pc_cpu_invalidate(struct usb_page_cache *pc) /* nothing has been loaded into this page cache! */ return; } - bus_dmamap_sync(pc->tag, pc->map, - BUS_DMASYNC_POSTWRITE | BUS_DMASYNC_POSTREAD); + bus_dmamap_sync(pc->tag, pc->map, BUS_DMASYNC_PREREAD); } /*------------------------------------------------------------------------* @@ -672,8 +671,7 @@ usb_pc_cpu_flush(struct usb_page_cache *pc) /* nothing has been loaded into this page cache! */ return; } - bus_dmamap_sync(pc->tag, pc->map, - BUS_DMASYNC_PREWRITE | BUS_DMASYNC_PREREAD); + bus_dmamap_sync(pc->tag, pc->map, BUS_DMASYNC_PREWRITE); } /*------------------------------------------------------------------------* -- Best regards. Piotr Ziecik _______________________________________________ freebsd-usb@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-usb To unsubscribe, send any mail to "freebsd-usb-unsubscr...@freebsd.org"