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

[David Miller <davem@davemloft.net>]

From: Krzysztof Halasa <khc@pm.waw.pl>
Date: Tue, 23 Oct 2007 01:40:18 +0200

> Jeff Garzik <jeff@garzik.org> writes:
> 
> > 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.

Right, and every vendor I've spoken to who had the INTX_DISABLE
bug clearly acknowledged that it was a bug in their RTL design
and that they considered the spec to be clear on this matter
in that INTX_DISABLE should not influence MSI in any way.

> 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 [...]

Things get more complicated with PCI-Express because INTx# isn't an
out-of-band "pin", but rather a message sent over the bus :-)