linux-kernel - Re: [PATCH v2] usb: host: xhci: Support running urb giveback in tasklet context

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Date:   Mon, 1 Apr 2019 10:43:24 -0400 (EDT)
From:   Alan Stern <stern@...land.harvard.edu>
To:     Suwan Kim <suwan.kim027@...il.com>
cc:     mathias.nyman@...ux.intel.com, <linux-usb@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <gregkh@...uxfoundation.org>
Subject: Re: [PATCH v2] usb: host: xhci: Support running urb giveback in
 tasklet context

On Mon, 1 Apr 2019, Suwan Kim wrote:

> Patch "USB: HCD: support giveback of URB in tasklet context"[1]
> introduced giveback of urb in tasklet context. [1] This patch was
> applied to ehci but not xhci. [2] This patch significantly reduces
> the hard irq time of xhci. Especially for uvc driver, the hard irq
> including the uvc completion function runs quite long but applying
> this patch reduces the hard irq time of xhci.

Please read the kerneldoc for usb_submit_urb() and usb_kill_urb(), in 
particular, the parts that describe how isochronous URBs are treated.  
Can you guarantee that with this patch applied, xhci-hcd will continue 
to work as the kerneldoc describes?

Alan Stern