When allocating URB memory with kmalloc(), drivers can simply set the
URB_FREE_BUFFER flag in urb::transfer_flags and that way, the memory
will be freed in the background when killing the URB (for example with
usb_kill_anchored_urbs()).
However, there are no equivalent mechanism when allocating DMA memory
(with usb_alloc_coherent()).
This patch adds a new flag: URB_FREE_COHERENT. Setting this flag will
cause the kernel to automatically call usb_free_coherent() on the
transfer buffer when the URB is killed, similarly to how
URB_FREE_BUFFER triggers a call to kfree().
In order to have all the flags in numerical order, URB_DIR_IN is
renumbered from 0x0200 to 0x0400 so that URB_FREE_COHERENT can reuse
value 0x0200.
CC: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>
CC: Rhett Aultman <rhett.aultman@xxxxxxxxxxx>
Signed-off-by: Vincent Mailhol <mailhol.vincent@xxxxxxxxxx>
---
Hi Rhett Aultman,
I put the code snippet I previously sent into a patch. It is not
tested (this is why I post it as RFC). Please feel free to add this to
your series.
** Changelog **
v1 -> v2:
* Renumber URB_DIR_IN for 0x0200 to 0x0400 in order to keep all the
flags in numerical order.
---
drivers/usb/core/urb.c | 3 +++
include/linux/usb.h | 3 ++-
2 files changed, 5 insertions(+), 1 deletion(-)
diff --git a/drivers/usb/core/urb.c b/drivers/usb/core/urb.c
index 33d62d7e3929..1460fdac0b18 100644
--- a/drivers/usb/core/urb.c
+++ b/drivers/usb/core/urb.c
@@ -22,6 +22,9 @@ static void urb_destroy(struct kref *kref)
if (urb->transfer_flags & URB_FREE_BUFFER)
kfree(urb->transfer_buffer);
+ else if (urb->transfer_flags & URB_FREE_COHERENT)
+ usb_free_coherent(urb->dev, urb->transfer_buffer_length,
+ urb->transfer_buffer, urb->transfer_dma);
kfree(urb);
}
diff --git a/include/linux/usb.h b/include/linux/usb.h
index 60bee864d897..945d68ea1d76 100644
--- a/include/linux/usb.h
+++ b/include/linux/usb.h
@@ -1328,9 +1328,10 @@ extern int usb_disabled(void);
#define URB_NO_INTERRUPT 0x0080 /* HINT: no non-error interrupt
* needed */
#define URB_FREE_BUFFER 0x0100 /* Free transfer buffer with the URB */
+#define URB_FREE_COHERENT 0x0200 /* Free DMA memory of transfer buffer */
/* The following flags are used internally by usbcore and HCDs */
-#define URB_DIR_IN 0x0200 /* Transfer from device to host */
+#define URB_DIR_IN 0x0400 /* Transfer from device to host */
#define URB_DIR_OUT 0
#define URB_DIR_MASK URB_DIR_IN
--
2.35.1
