[RFC/PATCH 2/2] usb: ffs/dwc3: pad epout buffer size when not aligned to maxpacketsize

[David Cohen <david.a.cohen@linux.intel.com>]

DWC3 requires buffer size to be aligned to maxpacketsize of an out
endpoint. ffs_epfile_io() needs to pad epout buffer to match above
condition if DWC3 controller is used.

This patch solves an specific situation but a more generic solution
should be found.

Signed-off-by: David Cohen <david.a.cohen@linux.intel.com>
---
 drivers/usb/gadget/f_fs.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/drivers/usb/gadget/f_fs.c b/drivers/usb/gadget/f_fs.c
index 75e4b78..33880e6 100644
--- a/drivers/usb/gadget/f_fs.c
+++ b/drivers/usb/gadget/f_fs.c
@@ -27,6 +27,7 @@
 #include <linux/usb/composite.h>
 #include <linux/usb/functionfs.h>
 
+#include "gadget_chips.h"
 
 #define FUNCTIONFS_MAGIC	0xa647361 /* Chosen by a honest dice roll ;) */
 
@@ -755,10 +756,12 @@ static ssize_t ffs_epfile_io(struct file *file,
 			     char __user *buf, size_t len, int read)
 {
 	struct ffs_epfile *epfile = file->private_data;
+	struct usb_gadget *gadget = epfile->ffs->gadget;
 	struct ffs_ep *ep;
 	char *data = NULL;
 	ssize_t ret;
 	int halt;
+	size_t orig_len = len;
 
 	goto first_try;
 	do {
@@ -794,6 +797,22 @@ first_try:
 			goto error;
 		}
 
+		/*
+		 * DWC3 requires buffer size to be aligned to maxpacketsize
+		 * of an out endpoint.
+		 * FIXME: a more generic solution might be necessary.
+		 */
+		if (gadget_is_dwc3(gadget) && read &&
+		    !IS_ALIGNED(len, ep->ep->desc->wMaxPacketSize)) {
+			size_t old_len = len;
+			len = roundup(orig_len,
+				      (size_t)ep->ep->desc->wMaxPacketSize);
+			if (unlikely(data) && len > old_len) {
+				kfree(data);
+				data = NULL;
+			}
+		}
+
 		/* Allocate & copy */
 		if (!halt && !data) {
 			data = kzalloc(len, GFP_KERNEL);
-- 
1.8.4.rc3