linux-kernel - Re: [PATCH] usb: enable pci MSI/MSIX in usb core

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Message-ID: <4F3E28D1.1030509@ladisch.de>
Date:	Fri, 17 Feb 2012 11:15:45 +0100
From:	Clemens Ladisch <clemens@...isch.de>
To:	"Alex,Shi" <alex.shi@...el.com>
CC:	Sarah Sharp <sarah.a.sharp@...ux.intel.com>,
	stern@...land.harvard.edu, Greg KH <gregkh@...uxfoundation.org>,
	linux-usb@...r.kernel.org, andiry.xu@....com,
	linux-kernel@...r.kernel.org, Oliver Neukum <oneukum@...e.de>,
	Takashi Iwai <tiwai@...e.de>, trenn@...e.de,
	linux-pci@...r.kernel.org, Michal Marek <MMarek@...e.com>
Subject: Re: [PATCH] usb: enable pci MSI/MSIX in usb core

Alex,Shi wrote:
>> The controller driver will need to know which of the multiple MSI-X
>> interrupts has been raised:
>>
>> irqreturn_t (*msix_irq)(struct usb_hcd *hcd, unsigned int nr_or_index);
>
> Actually, hcd has 2 object for msix, msix_count and msix_entries.
>
> Do you mean msix_count maybe smaller than we decide in hcd_setup_msix()?

No.  But when msic_count > 1, we have multiple interrupts.

> Which situation will make this?

Assume that an XHCI controller has two rings, and that each one gets its
own MSI-X interrupt.  How should the driver decide which of the rings
needs to be handled?

irqreturn_t xhci_msix_irq(struct usb_hcd *hcd)
{
	struct xhci_hcd *xhci = hcd_to_xhci(hcd);

	if (...)
		handle(xhci->ring[0]);
	else
		handle(xhci->ring[1]);
}

I.e., what should go into the if()?


Regards,
Clemens
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