usb: gadget: mass_storage: allow for deeper queue lengths

Instead of allowing a range of 2 to 4 requests,
let's allow the user choose up to 32 requests
as that will give us a better chance of keeping
controller busy.

We still maintain default of 2 so users shouldn't
be affected.

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

drivers/usb/gadget/Kconfig

@@ -113,7 +113,7 @@ config USB_GADGET_VBUS_DRAW
 
 config USB_GADGET_STORAGE_NUM_BUFFERS
 	int "Number of storage pipeline buffers"
-	range 2 4
+	range 2 32
 	default 2
 	help
 	   Usually 2 buffers are enough to establish a good buffering

drivers/usb/gadget/function/f_mass_storage.c

@@ -2662,10 +2662,12 @@ EXPORT_SYMBOL_GPL(fsg_common_put);
 /* check if fsg_num_buffers is within a valid range */
 static inline int fsg_num_buffers_validate(unsigned int fsg_num_buffers)
 {
-	if (fsg_num_buffers >= 2 && fsg_num_buffers <= 4)
+#define FSG_MAX_NUM_BUFFERS	32
+
+	if (fsg_num_buffers >= 2 && fsg_num_buffers <= FSG_MAX_NUM_BUFFERS)
 		return 0;
 	pr_err("fsg_num_buffers %u is out of range (%d to %d)\n",
-	       fsg_num_buffers, 2, 4);
+	       fsg_num_buffers, 2, FSG_MAX_NUM_BUFFERS);
 	return -EINVAL;
 }