usb: musb: introduce api for dma code to check compatibility with usb request

Gadget MUSB driver handles dma mappings in musb_gadget_queue(). Where as it is
possible for  dma code to reject the usb request later at ->channel_program()
called from txstate()/rxstate()

For example ->channel_program in tusb6010_omap.c:

static int tusb_omap_dma_program(struct dma_channel *channel, u16 packet_sz,
        u8 rndis_mode, dma_addr_t dma_addr, u32 len)
{
...
	if (unlikely(dma_addr & 0x1) || (len < 32) || (len > packet_sz))
		return false;
...
	if (dma_addr & 0x2)
		return false;
...
}

In this case, usb request will be handled in PIO mode which renders dma mapping
operations unnecessary.

This patch adds an api to allow dma code to indicate incompatibility with usb
request. Gadget musb driver call this api, if available, before dma mappings to
avoid any unnecessary mapping operations.
Signed-off-by: Mian Yousaf Kaukab <mian.yousaf.kaukab@stericsson.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>

drivers/usb/musb/musb_dma.h

@@ -169,6 +169,9 @@ struct dma_controller {
 							dma_addr_t dma_addr,
 							u32 length);
 	int			(*channel_abort)(struct dma_channel *);
+	int			(*is_compatible)(struct dma_channel *channel,
+							u16 maxpacket,
+							void *buf, u32 length);
 };
 
 /* called after channel_program(), may indicate a fault */

drivers/usb/musb/musb_gadget.c

@@ -100,11 +100,25 @@
 static inline void map_dma_buffer(struct musb_request *request,
 			struct musb *musb, struct musb_ep *musb_ep)
 {
+	int compatible = true;
+	struct dma_controller *dma = musb->dma_controller;
+
 	request->map_state = UN_MAPPED;
 
 	if (!is_dma_capable() || !musb_ep->dma)
 		return;
 
+	/* Check if DMA engine can handle this request.
+	 * DMA code must reject the USB request explicitly.
+	 * Default behaviour is to map the request.
+	 */
+	if (dma->is_compatible)
+		compatible = dma->is_compatible(musb_ep->dma,
+				musb_ep->packet_sz, request->request.buf,
+				request->request.length);
+	if (!compatible)
+		return;
+
 	if (request->request.dma == DMA_ADDR_INVALID) {
 		request->request.dma = dma_map_single(
 				musb->controller,