The HCD_NO_COHERENT_MEM USB host controller driver flag can be enabled
to instruct the USB stack to avoid allocating coherent memory for USB
buffers.
This flag is useful to overcome some esoteric memory access restrictions
found in some platforms.
For example, the Nintendo Wii video game console is a NOT_COHERENT_CACHE
platform that is unable to safely perform non-32 bit uncached writes
to RAM because the byte enables are not connected to the bus.
Thus, in that platform, "coherent" DMA buffers cannot be directly used
by the kernel code unless it guarantees that all write accesses
to said buffers are done in 32 bit chunks (which is not the case in the
USB subsystem).
To avoid this unwanted behaviour HCD_NO_COHERENT_MEM can be enabled at
the HCD controller, causing USB buffer allocations to be satisfied from
normal kernel memory. In this case, the USB stack will make sure that
the buffers get properly mapped/unmapped for DMA transfers using the DMA
streaming mapping API.
Note that other parts of the USB stack may also use coherent memory,
like for example the hardware descriptors used in the EHCI controllers.
This needs to be checked and addressed separately. In the EHCI example,
hardware descriptors are accessed in 32-bit (or 64-bit) chunks, causing
no problems in the described scenario.
Signed-off-by: Albert Herranz <albert_herranz@xxxxxxxx>
---
drivers/usb/core/buffer.c | 15 ++++++++-----
drivers/usb/core/hcd.c | 48 ++++++++++++++++++++++++++++++++++++++++----
drivers/usb/core/hcd.h | 13 ++++++-----
3 files changed, 59 insertions(+), 17 deletions(-)
diff --git a/drivers/usb/core/buffer.c b/drivers/usb/core/buffer.c
index 3ba2fff..fede7a0 100644
--- a/drivers/usb/core/buffer.c
+++ b/drivers/usb/core/buffer.c
@@ -53,8 +53,9 @@ int hcd_buffer_create(struct usb_hcd *hcd)
char name[16];
int i, size;
- if (!hcd->self.controller->dma_mask &&
- !(hcd->driver->flags & HCD_LOCAL_MEM))
+ if ((!hcd->self.controller->dma_mask &&
+ !(hcd->driver->flags & HCD_LOCAL_MEM)) ||
+ (hcd->driver->flags & HCD_NO_COHERENT_MEM))
return 0;
for (i = 0; i < HCD_BUFFER_POOLS; i++) {
@@ -109,8 +110,9 @@ void *hcd_buffer_alloc(
int i;
/* some USB hosts just use PIO */
- if (!bus->controller->dma_mask &&
- !(hcd->driver->flags & HCD_LOCAL_MEM)) {
+ if ((!bus->controller->dma_mask &&
+ !(hcd->driver->flags & HCD_LOCAL_MEM)) ||
+ (hcd->driver->flags & HCD_NO_COHERENT_MEM)) {
*dma = ~(dma_addr_t) 0;
return kmalloc(size, mem_flags);
}
@@ -135,8 +137,9 @@ void hcd_buffer_free(
if (!addr)
return;
- if (!bus->controller->dma_mask &&
- !(hcd->driver->flags & HCD_LOCAL_MEM)) {
+ if ((!bus->controller->dma_mask &&
+ !(hcd->driver->flags & HCD_LOCAL_MEM)) ||
+ (hcd->driver->flags & HCD_NO_COHERENT_MEM)) {
kfree(addr);
return;
}
diff --git a/drivers/usb/core/hcd.c b/drivers/usb/core/hcd.c
index a1cf3e4..7cc524a 100644
--- a/drivers/usb/core/hcd.c
+++ b/drivers/usb/core/hcd.c
@@ -1267,6 +1267,16 @@ static void unmap_urb_setup_packet(struct usb_hcd *hcd, struct urb *urb)
dma_unmap_single(hcd->self.controller, urb->setup_dma,
sizeof(struct usb_ctrlrequest),
DMA_TO_DEVICE);
+ /*
+ * For the HCD_NO_COHERENT_MEM case we need to reset
+ * setup_dma to its original value if the buffer was
+ * allocated via usb_buffer_alloc().
+ * This is necessary to force a new streaming DMA mapping
+ * when the same buffer is used again as the setup packet.
+ */
+ if ((hcd->driver->flags & HCD_NO_COHERENT_MEM) &&
+ (urb->transfer_flags & URB_NO_SETUP_DMA_MAP))
+ urb->setup_dma = ~(dma_addr_t)0;
} else if (urb->transfer_flags & URB_SETUP_BOUNCE_MAPPED) {
/* bounce from "local" memory */
urb->transfer_flags &= ~URB_SETUP_BOUNCE_MAPPED;
@@ -1290,6 +1300,16 @@ static void unmap_urb_transfer_buffer(struct usb_hcd *hcd, struct urb *urb)
urb->transfer_dma,
urb->transfer_buffer_length,
dir);
+ /*
+ * For the HCD_NO_COHERENT_MEM case we need to reset
+ * transfer_dma to its original value if the buffer was
+ * allocated via usb_buffer_alloc().
+ * This is necessary to force a new streaming DMA mapping
+ * when the same buffer is used again as a transfer buffer.
+ */
+ if ((hcd->driver->flags & HCD_NO_COHERENT_MEM) &&
+ (urb->transfer_flags & URB_NO_TRANSFER_DMA_MAP))
+ urb->transfer_dma = ~(dma_addr_t)0;
} else if (urb->transfer_flags & URB_TRANSFER_BOUNCE_MAPPED) {
/* bounce from "local" memory */
urb->transfer_flags &= ~URB_TRANSFER_BOUNCE_MAPPED;
@@ -1316,9 +1336,17 @@ static int urb_needs_setup_map(struct usb_hcd *hcd, struct urb *urb)
/* setup mappings are required only for control requests */
if (!usb_endpoint_xfer_control(&urb->ep->desc))
return 0;
-
- /* If the caller set URB_NO_SETUP_DMA_MAP then no mapping is needed */
- if ((urb->transfer_flags & URB_NO_SETUP_DMA_MAP))
+ /*
+ * Setup packets are 8 bytes long and don't use scatter/gather.
+ *
+ * If the caller sets URB_NO_SETUP_DMA_MAP and urb->setup_dma
+ * contains a valid DMA handle, then it is already mapped.
+ *
+ * urb->setup_dma is set to ~0 when allocating USB buffers for
+ * PIO-based or HCD_NO_COHERENT_MEM-based controllers.
+ */
+ if ((urb->transfer_flags & URB_NO_SETUP_DMA_MAP) &&
+ urb->transfer_dma != ~(dma_addr_t)0)
return 0;
return 1;
@@ -1330,8 +1358,18 @@ static int urb_needs_transfer_map(struct usb_hcd *hcd, struct urb *urb)
if (urb->transfer_buffer_length == 0)
return 0;
- /* If the caller set URB_NO_SETUP_DMA_MAP then no mapping is needed */
- if ((urb->transfer_flags & URB_NO_TRANSFER_DMA_MAP))
+ /* if this is a scatter/gather request, it should be already mapped */
+ if (urb->num_sgs > 0)
+ return 0;
+ /*
+ * If the caller sets URB_NO_TRANSFER_DMA_MAP and urb->transfer_dma
+ * contains a valid DMA handle, then it is already mapped.
+ *
+ * urb->transfer_dma is set to ~0 when allocating USB buffers for
+ * PIO-based or HCD_NO_COHERENT_MEM-based controllers.
+ */
+ if ((urb->transfer_flags & URB_NO_TRANSFER_DMA_MAP) &&
+ urb->transfer_dma != ~(dma_addr_t)0)
return 0;
return 1;
diff --git a/drivers/usb/core/hcd.h b/drivers/usb/core/hcd.h
index bbe2b92..cde42f3 100644
--- a/drivers/usb/core/hcd.h
+++ b/drivers/usb/core/hcd.h
@@ -183,12 +183,13 @@ struct hc_driver {
irqreturn_t (*irq) (struct usb_hcd *hcd);
int flags;
-#define HCD_MEMORY 0x0001 /* HC regs use memory (else I/O) */
-#define HCD_LOCAL_MEM 0x0002 /* HC needs local memory */
-#define HCD_USB11 0x0010 /* USB 1.1 */
-#define HCD_USB2 0x0020 /* USB 2.0 */
-#define HCD_USB3 0x0040 /* USB 3.0 */
-#define HCD_MASK 0x0070
+#define HCD_MEMORY 0x0001 /* HC regs use memory (else I/O) */
+#define HCD_LOCAL_MEM 0x0002 /* HC needs local memory */
+#define HCD_NO_COHERENT_MEM 0x0004 /* HC avoids use of "coherent" mem */
+#define HCD_USB11 0x0010 /* USB 1.1 */
+#define HCD_USB2 0x0020 /* USB 2.0 */
+#define HCD_USB3 0x0040 /* USB 3.0 */
+#define HCD_MASK 0x0070
/* called to init HCD and root hub */
int (*reset) (struct usb_hcd *hcd);
--
1.6.3.3
--
To unsubscribe from this list: send the line "unsubscribe linux-usb" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
