dwc_otg: checking the urb->transfer_buffer too early (#3332)

After enable the HIGHMEM and VMSPLIT_3G, the dwc_otg driver doesn't
work well on Pi2/3 boards with 1G physical ram. Users experience
the failure when copying a file of 600M size to the USB stick. And
at the same time, the dmesg shows:
usb 1-1.1.2: reset high-speed USB device number 8 using dwc_otg
sd 0:0:0:0: [sda] tag#0 FAILED Result: hostbyte=DID_ERROR driverbyte=DRIVER_OK
blk_update_request: I/O error, dev sda, sector 3024048 op 0x1:(WRITE) flags 0x4000 phys_seg 15 prio class 0

When this happens, the sg_buf sent to the driver is located in the
highmem region, the usb_sg_init() in the core/message.c will leave
transfer_buffer to NULL if the sg_buf is in highmem, but in the
dwc_otg driver, it returns -EINVAL unconditionally if transfer_buffer
is NULL.

The driver can handle the situation of buffer to be NULL, if it is in
DMA mode, it will convert an address from transfer_dma.

But if the conversion fails or it is in the PIO mode, we should check
buffer and return -EINVAL if it is NULL.

BugLink: https://bugs.launchpad.net/bugs/1852510
Signed-off-by: Hui Wang <hui.wang@canonical.com>

drivers/usb/host/dwc_otg/dwc_otg_hcd_linux.c

@@ -821,10 +821,6 @@ static int dwc_otg_urb_enqueue(struct usb_hcd *hcd,
 		dump_urb_info(urb, "dwc_otg_urb_enqueue");
 	}
 #endif
-
-	if (!urb->transfer_buffer && urb->transfer_buffer_length)
-		return -EINVAL;
-
 	if ((usb_pipetype(urb->pipe) == PIPE_ISOCHRONOUS)
 	    || (usb_pipetype(urb->pipe) == PIPE_INTERRUPT)) {
 		if (!dwc_otg_hcd_is_bandwidth_allocated
@@ -881,6 +877,13 @@ static int dwc_otg_urb_enqueue(struct usb_hcd *hcd,
 			      &urb->transfer_dma, buf);
 	}
 
+	if (!buf && urb->transfer_buffer_length) {
+		DWC_FREE(dwc_otg_urb);
+		DWC_ERROR("transfer_buffer is NULL in PIO mode or both "
+			   "transfer_buffer and transfer_dma are NULL in DMA mode\n");
+		return -EINVAL;
+	}
+
 	if (!(urb->transfer_flags & URB_NO_INTERRUPT))
 		flags |= URB_GIVEBACK_ASAP;
 	if (urb->transfer_flags & URB_ZERO_PACKET)