On Mon, 24 Jun 2013, Ming Lei wrote:
> This patch implements the mechanism of giveback of URB in
> tasklet context, so that hardware interrupt handling time for
> usb host controller can be saved much, and HCD interrupt handling
> can be simplified.
Changes from v1 to v2?
> +static void usb_giveback_urb_bh(unsigned long param)
> +{
> + struct giveback_urb_bh *bh = (struct giveback_urb_bh *)param;
> + unsigned long flags;
> + struct list_head local_list;
> +
> + spin_lock_irqsave(&bh->lock, flags);
> + bh->running = 1;
> + restart:
> + list_replace_init(&bh->head, &local_list);
> + spin_unlock_irqrestore(&bh->lock, flags);
Tasklet routines are always called with interrupts enabled, right?
Therefore you don't need to use the "flags" argument here or below.
> @@ -1667,25 +1721,40 @@ int usb_hcd_unlink_urb (struct urb *urb, int status)
> */
> void usb_hcd_giveback_urb(struct usb_hcd *hcd, struct urb *urb, int status)
> {
> - urb->hcpriv = NULL;
> - if (unlikely(urb->unlinked))
> - status = urb->unlinked;
> - else if (unlikely((urb->transfer_flags & URB_SHORT_NOT_OK) &&
> - urb->actual_length < urb->transfer_buffer_length &&
> - !status))
> - status = -EREMOTEIO;
> + struct giveback_urb_bh *bh;
> + bool sched, high_prio_bh;
>
> - unmap_urb_for_dma(hcd, urb);
> - usbmon_urb_complete(&hcd->self, urb, status);
> - usb_unanchor_urb(urb);
> + /* pass status to tasklet via unlinked */
> + if (likely(!urb->unlinked))
> + urb->unlinked = status;
>
> - /* pass ownership to the completion handler */
> - urb->status = status;
> - urb->complete (urb);
> - atomic_dec (&urb->use_count);
> - if (unlikely(atomic_read(&urb->reject)))
> - wake_up (&usb_kill_urb_queue);
> - usb_put_urb (urb);
> + if (!hcd_giveback_urb_in_bh(hcd) && !is_root_hub(urb->dev)) {
> + __usb_hcd_giveback_urb(urb);
> + return;
> + }
> +
> + if (usb_pipeisoc(urb->pipe) || usb_pipeint(urb->pipe)) {
> + bh = &hcd->high_prio_bh;
> + high_prio_bh = 1;
> + } else {
> + bh = &hcd->low_prio_bh;
> + high_prio_bh = 0;
> + }
Bool values should be assigned "true" or "false", not "1" or "0".
> +
> + spin_lock(&bh->lock);
> + list_add_tail(&urb->urb_list, &bh->head);
> + if (bh->running)
> + sched = 0;
> + else
> + sched = 1;
> + spin_unlock(&bh->lock);
How about calling this variable "running" instead of "sched"? Then you
could just say:
running = bh->running;
with no "if" statement.
> +
> + if (!sched)
> + ;
> + else if (high_prio_bh)
> + tasklet_hi_schedule(&bh->bh);
> + else
> + tasklet_schedule(&bh->bh);
> }
> EXPORT_SYMBOL_GPL(usb_hcd_giveback_urb);
>
> @@ -2307,6 +2376,42 @@ EXPORT_SYMBOL_GPL (usb_hc_died);
>
> /*-------------------------------------------------------------------------*/
>
> +static void __init_giveback_urb_bh(struct giveback_urb_bh *bh)
> +{
> +
> + spin_lock_init(&bh->lock);
> + INIT_LIST_HEAD(&bh->head);
> + tasklet_init(&bh->bh, usb_giveback_urb_bh, (unsigned long)bh);
> +}
> +
> +static void init_giveback_urb_bh(struct usb_hcd *hcd)
> +{
> + if (!hcd_giveback_urb_in_bh(hcd))
> + return;
As you mentioned, there's not much point in skipping this code when
it's not needed. In fact, you could just put the two lines below
directly into usb_create_shared_hcd(), and get rid of the "__" from the
beginning of the name.
> +
> + __init_giveback_urb_bh(&hcd->high_prio_bh);
> + __init_giveback_urb_bh(&hcd->low_prio_bh);
> +}
> +
> +static void exit_giveback_urb_bh(struct usb_hcd *hcd)
> +{
> + if (!hcd_giveback_urb_in_bh(hcd))
> + return;
> +
> + /*
> + * tasklet_kill() isn't needed here because:
> + * - driver's disconnec() called from usb_disconnect() should
Misspelled "disconnect".
> + * make sure its URBs are completed during the disconnect()
> + * callback
> + *
> + * - it is too late to run complete() here since driver may have
> + * been removed already now
> + *
> + * Using tasklet to run URB's complete() doesn't change this
> + * behavior of usbcore.
> + */
> +}
Why have a separate subroutine for doing nothing? Simply put this
comment directly into usb_remove_hcd(). (And you can remove the last
two lines of the comment; they don't make sense in this context.)
Alan Stern
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