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| author | Roman Kagan <rkagan@mail.ru> | 2005-05-06 00:55:56 +0400 |
|---|---|---|
| committer | Greg KH <gregkh@suse.de> | 2005-06-03 00:04:30 -0700 |
| commit | 719df469cb51199316ae2a11c75a8046be34b899 (patch) | |
| tree | 8f96e3713ad52b9308f22a464da14a1d7a685675 /include/linux/usb.h | |
| parent | 1724757e5ab5219b46876ac6e4e362a4b2dcfa86 (diff) | |
| download | lwn-719df469cb51199316ae2a11c75a8046be34b899.tar.gz lwn-719df469cb51199316ae2a11c75a8046be34b899.zip | |
[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>
Diffstat (limited to 'include/linux/usb.h')
| -rw-r--r-- | include/linux/usb.h | 6 |
1 files changed, 5 insertions, 1 deletions
diff --git a/include/linux/usb.h b/include/linux/usb.h index 41d1a644c9d4..2d1ac5058534 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 */ |