Hi Geert-san,
Thank you for the reply again!
> Hi Shimoda-san,
>
> On Mon, Feb 16, 2015 at 2:52 AM, Yoshihiro Shimoda
> <yoshihiro.shimoda.uh@xxxxxxxxxxx> wrote:
> > According to the gadget.h, a "complete" function will always be called
> > with interrupts disabled. However, sometimes usbhsg_queue_pop() function
> > is called with interrupts enabled. So, this function should calls
> > local_irq_save() before this calls the usb_gadget_giveback_request().
> > Otherwise, there is possible to cause a spinlock suspected in a gadget
> > complete function.
>
> I still feel uneasy about adding the call to local_irq_save(), as the need for
> this is usually an indicator of another locking problem.
I also think that I would like to avoid using local_irq_save().
But, I have no idea to resolve this issue for now.
> Unfortunately I know next to nothing about the USB gadget subsystem, so some
> help from the USB gadget experts would be appreciated.
>
> I had a look at other drivers, and it seems most drivers actually release
> and reacquire a spinlock around the call to usb_gadget_giveback_request(),
> i.e. they do:
>
> spin_unlock(...);
> usb_gadget_giveback_request(...);
> spin_lock();
>
> This means they had already acquired the spinlock (and disabled interrupts!)
> before, which looks much healthier to me.
>
> There's only one driver that uses local_irq_save() (pxa27x_udc).
I had a look at the musb driver. It uses a dmaengine driver.
And, in the callback routine of the musb driver, it calls spin_lock_irqsave() at first.
cppi41_dma_callback
--> spin_lock_irqsave(&musb->lock, flags);
--> cppi41_trans_done
--> musb_dma_completion
--> musb_g_tx or musb_g_rx
--> musb_g_giveback
--> spin_unlock(&musb->lock); # This means unlocked the spin, but disabled interrupts.
--> usb_gadget_giveback_request
--> spin_lock(&musb->lock);
< snip >
--> spin_unlock_irqrestore(&musb->lock, flags);
So, about disabled interrupts before usb_gadget_giveback_request(),
it is similar with this patch.
Best regards,
Yoshihiro Shimoda
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