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authorRoman Kagan <rkagan@mail.ru>2005-05-06 00:55:56 +0400
committerGreg KH <gregkh@suse.de>2005-06-03 00:04:30 -0700
commit719df469cb51199316ae2a11c75a8046be34b899 (patch)
tree8f96e3713ad52b9308f22a464da14a1d7a685675
parent1724757e5ab5219b46876ac6e4e362a4b2dcfa86 (diff)
[PATCH] USB: update urb documentation
On Wed, May 04, 2005 at 01:37:30PM -0700, David Brownell wrote: > On Wednesday 04 May 2005 12:19 pm, Roman Kagan wrote: > > struct urb { > > /* private, usb core and host controller only fields in the urb */ > > ... > > struct list_head urb_list; /* list pointer to all active urbs */ > > ... > > }; > > > > Is it safe to use it for driver's purposes when the driver owns the urb, > > that is, starting from the completion routine until the urb is submitted > > with usb_submit_urb()? > > Right now, it should be. Great! FWIW I've briefly tested a modified version of usbatm using the list head in struct urb instead of creating a wrapper struct, and I haven't seen any failures yet. So I tend to believe that your "should be" actually means "is" :) > > If it is, can it be guaranteed in future, e.g. > > by moving the list head into the public section of struct urb? > > In fact I'm not sure why it ever got called "private" to usbcore/hcds. > I thought the idea was that it should be like urb->status, reserved for > whoever controls the URB. OK then how about the following (essentially documentation) patch? Signed-off-by: Roman Kagan <rkagan@mail.ru> Acked-by: David Brownell <david-b@pacbell.net> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
-rw-r--r--include/linux/usb.h6
1 files changed, 5 insertions, 1 deletions
diff --git a/include/linux/usb.h b/include/linux/usb.h
index 41d1a644c9d..2d1ac505853 100644
--- a/include/linux/usb.h
+++ b/include/linux/usb.h
@@ -796,6 +796,10 @@ typedef void (*usb_complete_t)(struct urb *, struct pt_regs *);
* of the iso_frame_desc array, and the number of errors is reported in
* error_count. Completion callbacks for ISO transfers will normally
* (re)submit URBs to ensure a constant transfer rate.
+ *
+ * Note that even fields marked "public" should not be touched by the driver
+ * when the urb is owned by the hcd, that is, since the call to
+ * usb_submit_urb() till the entry into the completion routine.
*/
struct urb
{
@@ -803,12 +807,12 @@ struct urb
struct kref kref; /* reference count of the URB */
spinlock_t lock; /* lock for the URB */
void *hcpriv; /* private data for host controller */
- struct list_head urb_list; /* list pointer to all active urbs */
int bandwidth; /* bandwidth for INT/ISO request */
atomic_t use_count; /* concurrent submissions counter */
u8 reject; /* submissions will fail */
/* public, documented fields in the urb that can be used by drivers */
+ struct list_head urb_list; /* list head for use by the urb owner */
struct usb_device *dev; /* (in) pointer to associated device */
unsigned int pipe; /* (in) pipe information */
int status; /* (return) non-ISO status */