[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>
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@ -796,6 +796,10 @@ typedef void (*usb_complete_t)(struct urb *, struct pt_regs *);
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* of the iso_frame_desc array, and the number of errors is reported in
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* error_count. Completion callbacks for ISO transfers will normally
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* (re)submit URBs to ensure a constant transfer rate.
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*
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* Note that even fields marked "public" should not be touched by the driver
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* when the urb is owned by the hcd, that is, since the call to
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* usb_submit_urb() till the entry into the completion routine.
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*/
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struct urb
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{
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@ -803,12 +807,12 @@ struct urb
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struct kref kref; /* reference count of the URB */
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spinlock_t lock; /* lock for the URB */
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void *hcpriv; /* private data for host controller */
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struct list_head urb_list; /* list pointer to all active urbs */
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int bandwidth; /* bandwidth for INT/ISO request */
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atomic_t use_count; /* concurrent submissions counter */
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u8 reject; /* submissions will fail */
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/* public, documented fields in the urb that can be used by drivers */
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struct list_head urb_list; /* list head for use by the urb owner */
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struct usb_device *dev; /* (in) pointer to associated device */
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unsigned int pipe; /* (in) pipe information */
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int status; /* (return) non-ISO status */
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