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

[Andiry Xu <andiry.xu@amd.com>]

On 02/17/2012 06:15 PM, Clemens Ladisch wrote:
> 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()?
> 
> 

Currently xHCI driver only support one ERST event ring. If we need to
support multiple event rings in the future, it's simple: in
usb_hcd_request_msi_msix_irqs, change the last parameter of
request_irq() to xhci->erst[i], and we can get the corresponding erst[i]
in xhci_msi_irq() like this:

irqreturn_t xhci_msi_irq(int irq, void *dev_id)
{
	struct xhci_erst *erst = dev_id;
	...
	/* Handle corresponding event ring pointed by erst */
}

See Matthew Wilcox's patchset below for reference:

www.spinics.net/lists/linux-usb/msg47353.html

Thanks,
Andiry
Andiry