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path: root/drivers/usb/musb/musb_gadget.c
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Diffstat (limited to 'drivers/usb/musb/musb_gadget.c')
-rw-r--r--drivers/usb/musb/musb_gadget.c30
1 files changed, 26 insertions, 4 deletions
diff --git a/drivers/usb/musb/musb_gadget.c b/drivers/usb/musb/musb_gadget.c
index d0b87e7b4abf..b6b84dacc791 100644
--- a/drivers/usb/musb/musb_gadget.c
+++ b/drivers/usb/musb/musb_gadget.c
@@ -707,11 +707,12 @@ static void rxstate(struct musb *musb, struct musb_request *req)
fifo_count = musb_readw(epio, MUSB_RXCOUNT);
/*
- * use mode 1 only if we expect data of at least ep packet_sz
- * and have not yet received a short packet
+ * Enable Mode 1 on RX transfers only when short_not_ok flag
+ * is set. Currently short_not_ok flag is set only from
+ * file_storage and f_mass_storage drivers
*/
- if ((request->length - request->actual >= musb_ep->packet_sz) &&
- (fifo_count >= musb_ep->packet_sz))
+
+ if (request->short_not_ok && fifo_count == musb_ep->packet_sz)
use_mode_1 = 1;
else
use_mode_1 = 0;
@@ -727,6 +728,27 @@ static void rxstate(struct musb *musb, struct musb_request *req)
c = musb->dma_controller;
channel = musb_ep->dma;
+ /* We use DMA Req mode 0 in rx_csr, and DMA controller operates in
+ * mode 0 only. So we do not get endpoint interrupts due to DMA
+ * completion. We only get interrupts from DMA controller.
+ *
+ * We could operate in DMA mode 1 if we knew the size of the tranfer
+ * in advance. For mass storage class, request->length = what the host
+ * sends, so that'd work. But for pretty much everything else,
+ * request->length is routinely more than what the host sends. For
+ * most these gadgets, end of is signified either by a short packet,
+ * or filling the last byte of the buffer. (Sending extra data in
+ * that last pckate should trigger an overflow fault.) But in mode 1,
+ * we don't get DMA completion interrupt for short packets.
+ *
+ * Theoretically, we could enable DMAReq irq (MUSB_RXCSR_DMAMODE = 1),
+ * to get endpoint interrupt on every DMA req, but that didn't seem
+ * to work reliably.
+ *
+ * REVISIT an updated g_file_storage can set req->short_not_ok, which
+ * then becomes usable as a runtime "use mode 1" hint...
+ */
+
/* Experimental: Mode1 works with mass storage use cases */
if (use_mode_1) {
csr |= MUSB_RXCSR_AUTOCLEAR;