linux-kernel - Re: [PATCH] PCI: Add support for multiple MSI

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Date:	Sat, 12 Jul 2008 13:45:42 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>
Cc:	Matthew Wilcox <matthew@....cx>, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org, grundler@...isc-linux.org,
	mingo@...e.hu, tglx@...utronix.de, jgarzik@...ox.com,
	linux-ide@...r.kernel.org, suresh.b.siddha@...el.com,
	jbarnes@...tuousgeek.org, rdunlap@...otime.net,
	mtk.manpages@...il.com, Matthew Wilcox <willy@...ux.intel.com>
Subject: Re: [PATCH] PCI: Add support for multiple MSI

On Fri, 2008-07-11 at 17:28 +0900, Hidetoshi Seto wrote:
> Hi,
> 
> First of all, it seems that mask/unmask of MSI has problems.
>  - Per-vector masking is optional for MSI, so I think that allocating
>    multiple messages for a function without masking capability would be
>    not good idea, since all vector in the block will be masked/unmasked
>    at once without any agreement.
>  - Even if the function supports per-vector masking, current
>    mask/unmask_msi_irq() functions assume that MSI uses only one vector,
>    therefore they only set/unset the first bit of the maskbits which
>    for the first vector of the block.  The bits for other vectors are
>    initialized as 'masked' but no one unmask them.

I tend to think we should just do soft-masking anyway for MSI... better
than whacking config space.

Ben

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