linux-kernel - Re: [PATCH 1/2] msi: Invert the sense of the MSI enables.

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Date:	Thu, 24 May 2007 23:59:47 -0600
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	michael@...erman.id.au
Cc:	Greg Kroah-Hartman <gregkh@...e.de>,
	Jay Cliburn <jacliburn@...lsouth.net>,
	Grzegorz Krzystek <ninex@...eX.eu.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andi Kleen <ak@...e.de>, ninex@...pl,
	linux-kernel@...r.kernel.org, linux-pci@...ey.karlin.mff.cuni.cz,
	David Miller <davem@...emloft.net>,
	Tony Luck <tony.luck@...el.com>
Subject: Re: [PATCH 1/2] msi: Invert the sense of the MSI enables.

Michael Ellerman <michael@...erman.id.au> writes:

> On Thu, 2007-05-24 at 22:19 -0600, Eric W. Biederman wrote:
>> Currently we blacklist known bad msi configurations which means we
>> keep getting MSI enabled on chipsets that either do not support MSI,
>> or MSI is implemented improperly.  Since the normal IRQ routing
>> mechanism seems to works even when MSI does not, this is a bad default
>> and causes non-functioning systems for no good reason.
>> 
>> So this patch inverts the sense of the MSI bus flag to only enable
>> MSI on known good systems.  I am seeding that list with the set of
>> chipsets with an enabled hypertransport MSI mapping capability.  Which
>> is as close as I can come to an generic MSI enable.  So for actually
>> using MSI this patch is a regression, but for just having MSI enabled
>> in the kernel by default things should just work with this patch
>> applied.
>
> I guess this is a good idea for random x86 machines. On powerpc I think
> we'll just turn it on for every bus, and let the existing per-platform
> logic decide.

Yep.  That is pretty much what I expected.

Since you already have to detect how to implement the MSI methods
you need a separate white list anyway.

Just a side note.  This only needs to be enabled for pci root
busses.

Eric
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