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

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Date:	Tue, 30 Jan 2007 07:22:38 +1100
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	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


> This is the most straight forward and handles machines with really
> weird msi setups, so I lean in this direction.
> 
> The question is there anything at all we can do generically?
> 
> I can't see a case where ppc_md would not wind up with the hooks
> that decide if it is a hypervisor or not.  Even if we came up
> with a better set of functions you need to hook.

Sure, but with Michael's approach, the only hook was get_msi_ops(pdev) 

Anyway, there isn't -that- much that can be done generically in the HV
case. Mostly some argument sanity checking, the logic for saving &
restoring pdev->irq for MSIs, that sort of thing.

> Ok. I think I get the point of check.  I believe I need to look at your
> code a little more and see what you are doing to see if there is anything
> generic worth doing, that we can always do outside of architecture code
> no matter how much of the job the Hypervisor wants to do for us.

I understand.

> I'd hate to hit a different Hypervisor that did something close but
> not quite the same and have the code fail then.  So definitely
> avoiding touching pci config space at all in the calls seems to make a
> lot of sense.  This includes avoiding pci_find_capability right?

Quite possibly yes. I'm pretty sure it will work on IBM HV but we aren't
really supposed to use it...

> Off the top of my head the only things we can do generically are
> some data structure things and flags like dev->msi_enabled or
> dev->msix_enabled.

That and the saving & restoring of pdev->irq. That is not very much.

> Anyway have a nice night and more in the morning.

Ben.

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