linux-kernel - Re: [PATCH 5/6] USB: Support wakeup IRQ for suspended controllers

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Date:	Wed, 10 Jul 2013 14:45:02 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Roger Quadros <rogerq@...com>
cc:	gregkh@...uxfoundation.org, <balbi@...com>,
	<sergei.shtylyov@...entembedded.com>, <khilman@...aro.org>,
	<tony@...mide.com>, <ruslan.bilovol@...com>,
	<linux-usb@...r.kernel.org>, <linux-omap@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 5/6] USB: Support wakeup IRQ for suspended controllers

On Wed, 10 Jul 2013, Roger Quadros wrote:

> Some platforms e.g. ehci-omap can generate an interrupt
> (i.e. remote wakeup) even when the controller is suspended i.e.
> HW_ACCESSIBLE is cleared.
> 
> Introduce a flag "has_wakeup_irq" in struct usb_hcd to indicate
> such cases.
> 
> We tackle this case by disabling the IRQ, scheduling a
> hub resume and enabling back the IRQ after the controller has
> resumed. This ensures that the IRQ handler runs only after the
> controller is accessible.

> @@ -2248,7 +2253,21 @@ irqreturn_t usb_hcd_irq (int irq, void *__hcd)
>  	 */
>  	local_irq_save(flags);
>  
> -	if (unlikely(HCD_DEAD(hcd) || !HCD_HW_ACCESSIBLE(hcd)))
> +	if (unlikely(HCD_DEAD(hcd)))
> +		rc = IRQ_NONE;
> +	else if (unlikely(!HCD_HW_ACCESSIBLE(hcd) && hcd->has_wakeup_irq)) {
> +		/*
> +		 * We got a wakeup interrupt while the controller was
> +		 * suspending or suspended.  We can't handle it now, so
> +		 * disable the IRQ and resume the root hub (and hence
> +		 * the controller too).
> +		 */
> +		disable_irq_nosync(hcd->irq);
> +		set_bit(HCD_FLAG_IRQ_DISABLED, &hcd->flags);
> +		usb_hcd_resume_root_hub(hcd);
> +
> +		rc = IRQ_HANDLED;
> +	} else if (unlikely(!HCD_HW_ACCESSIBLE(hcd)))
>  		rc = IRQ_NONE;

In the interest of minimizing the amount of work needed in the most 
common case, this should be written as:

	else if (unlikely(!HCD_HW_ACCESSIBLE(hcd))) {
		if (hcd->has_wakeup_irq) {
			...
		} else
			rc = IRQ_NONE;

>  	else if (hcd->driver->irq(hcd) == IRQ_NONE)
>  		rc = IRQ_NONE;

Apart from that, the patch is okay.  When you rearrange the logic, you 
can add my Acked-by.

Alan Stern

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