linux-kernel - Re: [PATCH] ALSA: hda-intel - Disable MSI support by default

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Date:	Wed, 15 Nov 2006 14:20:47 -0500
From:	Jeff Garzik <jeff@...zik.org>
To:	Linus Torvalds <torvalds@...l.org>
CC:	Krzysztof Halasa <khc@...waw.pl>,
	David Miller <davem@...emloft.net>,
	linux-kernel@...r.kernel.org, tiwai@...e.de,
	Olivier Nicolas <olivn@...llprod.org>
Subject: Re: [PATCH] ALSA: hda-intel - Disable MSI support by default

Linus Torvalds wrote:
> However, I really think that this should be a generic PCI layer thing. If 
> some device asks for MSI interrupts, the PCI layer should try to turn off 
> a INTx routing on its own. Asking drivers to do both is just silly, 
> especially since driver writers really shouldn't be expected to know about 
> all these issues (sure, the best ones do, but a lot of driver writers will 
> just say "it works for me").
> 
> So I don't think the HDA driver should need disable INTx on its own 
> explicitly.

Your thinking is correct, but there is one hitch.

As Roland noted, PCI layer /already/ does this for PCI-Express devices.

The reason we cannot do this in the generic layer for non-PCI-Ex is only 
the driver knows whether that PCI 2.2 bit was actually implemented in 
the device or mapped to some other weird behavior we don't want to 
touch.  DISABLE-INTX is a new bit not present in PCI 2.1 (alas!!).

pci_intx() was my five minute solution to this problem, and it got moved 
outside of libata as soon as somebody needed the same thing :)

Maybe a better solution is letting the driver say "pci_dev->intx_ok = 1" 
right before it calls pci_enable_device().

And if we do this, we can follow through on another suggestion I made: 
disabling INTx on driver exit, to help eliminate any possibility of 
screaming interrupts after driver unload.

	Jeff

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