linux-kernel - Re: [PATCH 0/6] MSI portability cleanups

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Message-Id: <1170102731.26655.277.camel@localhost.localdomain>
Date:	Tue, 30 Jan 2007 07:32:10 +1100
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	michael@...erman.id.au
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	David Miller <davem@...emloft.net>, jeff@...zik.org,
	greg@...ah.com, tony.luck@...el.com, grundler@...isc-linux.org,
	mingo@...e.hu, linux-kernel@...r.kernel.org, kyle@...isc-linux.org,
	linuxppc-dev@...abs.org, brice@...i.com, shaohua.li@...el.com,
	linux-pci@...ey.karlin.mff.cuni.cz
Subject: Re: [PATCH 0/6] MSI portability cleanups


> You can read config space, but it's not clear to me if the HV is allowed
> to filter it and hide things. 

I've seen it do it for example with EADS bridges. I haven't seen doing
it with devices (other than hiding entire functions) but I wouldn't
exclude it...

> It's also possible that the device
> supports MSI, but for some reason the HV doesn't allow it on that device
> etc. so you really have to ask the HV if it's enabled. So pci_find_cap()
> shouldn't crash or anything, but it may lie to you.

Yup.

> One thing I did like about my code, is that pci_enable_msi() and
> pci_enable_msix() are just small wrappers around generic_enable_msi() -
> which does all the work, and is the same regardless of whether it's an
> MSI or MSI-X. Although that's facilitated by the type arg which you
> don't like.

Part of the reason is you make MSI look like MSI-X (a vector of 1 entry)
while Eric does the opposite.

Ben.


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