linux-kernel - Re: [patch] PCI: disable MSI on more ATI NorthBridges

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Message-ID: <471DC95D.2060501@garzik.org>
Date:	Tue, 23 Oct 2007 06:13:49 -0400
From:	Jeff Garzik <jeff@...zik.org>
To:	Krzysztof Halasa <khc@...waw.pl>
CC:	Daniel Barkalow <barkalow@...ervon.org>,
	Linas Vepstas <linas@...tin.ibm.com>,
	Shane Huang <chunhao.huang@...mail.com>, davem@...emloft.net,
	gregkh@...e.de, htejun@...il.com, brice.goglin@...il.com,
	david.gaarenstroom@...il.com, linux-kernel@...r.kernel.org,
	linux-pci@...ey.karlin.mff.cuni.cz, shane.huang@....com,
	linux-ide@...r.kernel.org, Brice Goglin <brice@...i.com>
Subject: Re: [patch] PCI: disable MSI on more ATI NorthBridges

Krzysztof Halasa wrote:
> Jeff Garzik <jeff@...zik.org> writes:
> 
>> Note that INTX_DISABLE is a recent addition to PCI.
> 
> It's PCI 2.3.

Yes.


>>  Older PCI devices
>> support neither MSI nor INTX-disable, so make sure such devices don't
>> creep into your sample.
> 
> MSI has been introduced by PCI 2.2 (and thus PCI-X 1.0) so there may
> be devices with MSI but without INTx-disable bit. I guess I have some
> early PCI-X hardware with MSI but I don't know if they have INTx-disable
> bit and I can't currently test that.
> And it probably doesn't matter.

Time will tell :)


>> In general it is documented that INTX_DISABLE should apply only to
>> INTx# so devices that disable MSI based on that bit are out of spec.
> 
> The wording is:
> 10: This bit disables the device from asserting INTx#. A value of 0
> enables the assertion of its INTx# signal. A value of 1 disables the
> assertion of its INTx# signal. This bit's state after RST# is 0. Refer
> to Section 6.8.1.3 for control of MSI.
> 
> So strictly speaking it mandates disabling/enabling INTx but says
> nothing about other things (e.g. MSI). Some common sense dictates
> it shouldn't disable MSI, I guess.
> 
> The "MSI Enable" description doesn't leave any doubt:
> 0: MSI Enable: If 1, the function is permitted to use MSI to request
> service and is prohibited from using its INTx# pin [...]

Right.  I was merely describing the end result, the union of that 
language as it applies to the kernel.

	Jeff


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