Revert "usb: musb: use DMA mode 1 whenever possible"

This reverts commit 4f3e8d263d34e52e75b5adfa14811467d3033d8e.

it turns out that current implementation of Mode 1
DMA added a few regressions to some users, so we
need to revert this patch and let author work on
a better version of Mode 1 DMA support.

Signed-off-by: Felipe Balbi <balbi@ti.com>

diff --git a/drivers/usb/musb/musb_gadget.c b/drivers/usb/musb/musb_gadget.c
index d0b87e7..b6b84da 100644 (file)
--- 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;