On Wed, 23 Mar 2016, yoma sophian wrote:
> hi Alan:
> 2016-03-04 23:25 GMT+08:00 Alan Stern <st...@rowland.harvard.edu>:
> > On Fri, 4 Mar 2016, yoma sophian wrote:
> >
> >> BTW, when I disable BH support in hcd driver.
> >> I get below recursion of spin lock sometimes.
> >> Did I missing anything once disable BH?
> >
> > Yes, you missed a very important fact: ehci-hcd _requires_ BH support!
> if so, why we still keep below part of code that will never run under
> BH enabled.
>
> if (!hcd_giveback_urb_in_bh(hcd) && !is_root_hub(urb->dev)) {
> __usb_hcd_giveback_urb(urb);
> return;
> }
Where is that code? Not anywhere in ehci-*.c. Are you talking about
drivers/usb/core/hcd.c? That file interacts with other drivers besides
ehci-hcd, and many of those other drivers do not have BH support.
However, it's true that ehci-hcd does contain some code that will never
get used with BH givebacks enabled. I haven't tried to remove this
code because it doesn't create any problems (although perhaps I
should).
Alan Stern
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