Martin Fuzzey a écrit :
We don't want to add support for this to DMA bounce. DMA bounce is already
a pain in the backside and causes its own set of problems - please let it
die a long slow but quite death.
If you want to see the kind of pain dmabounce causes, look at this long
standing and as yet unsolved bug:
http://bugzilla.kernel.org/show_bug.cgi?id=7760
Well I don't know the dmabounce code but why is using it likely to cause
OOM problems (at least why more so than copying the buffer in the HCD or
the usb core). In both cases there will be two copies of the buffer in
memory which could I agree be a problem in memory constrained systems.
But if we _do_ want to accept unaligned buffers from usb drivers I can't
see a way round that.
memmove is our friend :
the buffer allocated in usbnet got an offset.
All you have to do it remove this offset and memmove the data. That what
I did [1], and why it is better to do it in usb driver.
Matthieu
[1] http://article.gmane.org/gmane.linux.usb.general/28700
diff --git a/drivers/usb/gadget/gadget_chips.h b/drivers/usb/gadget/gadget_chips.h
index 1edbc12..ed3ee67 100644
--- a/drivers/usb/gadget/gadget_chips.h
+++ b/drivers/usb/gadget/gadget_chips.h
@@ -214,4 +214,14 @@ static inline bool gadget_supports_altsettings(struct usb_gadget *gadget)
return true;
}
+/**
+ * gadget_dma32 - return true if we want buffer aligned on 32 bits (for dma)
+ * @gadget: the gadget in question
+ */
+static inline bool gadget_dma32(struct usb_gadget *gadget)
+{
+ if (gadget_is_musbhdrc(gadget))
+ return true;
+ return false;
+}
#endif /* __GADGET_CHIPS_H */
diff --git a/drivers/usb/gadget/u_ether.c b/drivers/usb/gadget/u_ether.c
index 84ca195..697af90 100644
--- a/drivers/usb/gadget/u_ether.c
+++ b/drivers/usb/gadget/u_ether.c
@@ -249,7 +249,12 @@ rx_submit(struct eth_dev *dev, struct usb_request *req, gfp_t gfp_flags)
* but on at least one, checksumming fails otherwise. Note:
* RNDIS headers involve variable numbers of LE32 values.
*/
- skb_reserve(skb, NET_IP_ALIGN);
+ /*
+ * RX: Do not move data by IP_ALIGN:
+ * if your DMA controller cannot handle it
+ */
+ if (!gadget_dma32(dev->gadget))
+ skb_reserve(skb, NET_IP_ALIGN);
req->buf = skb->data;
req->length = size;
@@ -282,6 +287,12 @@ static void rx_complete(struct usb_ep *ep, struct usb_request *req)
/* normal completion */
case 0:
skb_put(skb, req->actual);
+ if (gadget_dma32(dev->gadget) && NET_IP_ALIGN) {
+ u8 *data = skb->data;
+ size_t len = skb_headlen(skb);
+ skb_reserve(skb, NET_IP_ALIGN);
+ memmove(skb->data, data, len);
+ }
if (dev->unwrap) {
unsigned long flags;
@@ -573,6 +584,24 @@ static netdev_tx_t eth_start_xmit(struct sk_buff *skb,
length = skb->len;
}
+
+ /*
+ * Align data to 32bit if the dma controller requires it
+ */
+ if (gadget_dma32(dev->gadget)) {
+ unsigned long align = (unsigned long)skb->data & 3;
+ if (WARN_ON(skb_headroom(skb) < align)) {
+ dev_kfree_skb_any(skb);
+ goto drop;
+ } else if (align) {
+ u8 *data = skb->data;
+ size_t len = skb_headlen(skb);
+ skb->data -= align;
+ memmove(skb->data, data, len);
+ skb_set_tail_pointer(skb, len);
+ }
+ }
+
req->buf = skb->data;
req->context = skb;
req->complete = tx_complete;
