linux-kernel - Re: [PATCH] usb: correctly enable interrupts for xhci

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Date:	Fri, 1 Mar 2013 09:54:42 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Hannes Reinecke <hare@...e.de>
cc:	linux-usb@...r.kernel.org, <linux-kernel@...r.kernel.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Oliver Neukum <oneukum@...e.de>,
	Thomas Renninger <trenn@...e.de>,
	Yinghai Lu <yinghai@...nel.org>,
	Frederik Himpe <fhimpe@....ac.be>,
	David Haerdeman <david@...deman.nu>
Subject: Re: [PATCH] usb: correctly enable interrupts for xhci

On Fri, 1 Mar 2013, Hannes Reinecke wrote:

> xhci might run with MSI/MSI-X only, with no support for legacy
> interrupts. On these devices the request_irq() call in usb_add_hcd()
> will fail, causing the entire device to fail.
> For xhci this is especially painful as the driver will enable
> interrupts during xhci_run(), so the initial call to request_irq()
> is not required anyway.
> 
> This patch adds a flag 'msix_supported' to struct usb_hcd, which
> will cause usb_add_hcd() to skip interrupt setup. This flag is
> set in xhci-pci, so the registration will skip the first request_irq()
> and can proceed.

I think it might be better to fix this in hcd-pci.c:usb_hcd_pci_probe.  
At that point if we see that MSI/MSI-X is available, the call to 
usb_add_hcd can pass 0 instead of dev->irq.

It may even be possible to do this without adding an extra flag 
anywhere.  It also has the advantage of keeping special knowledge about 
MSI encapsulated in the PCI-specific parts of the code.

Alan Stern

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