linux-kernel - Re: [PATCH 1/3] iommu/core: add fault reporting mechanism

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Message-ID: <20110913100034.GJ11701@amd.com>
Date:	Tue, 13 Sep 2011 12:00:34 +0200
From:	"Roedel, Joerg" <Joerg.Roedel@....com>
To:	Ohad Ben-Cohen <ohad@...ery.com>
CC:	"iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
	"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>,
	Hiroshi DOYU <Hiroshi.DOYU@...ia.com>,
	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	David Woodhouse <dwmw2@...radead.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	David Brown <davidb@...eaurora.org>,
	Arnd Bergmann <arnd@...db.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/3] iommu/core: add fault reporting mechanism

On Mon, Sep 12, 2011 at 12:21:13PM -0400, Ohad Ben-Cohen wrote:
> On Mon, Sep 12, 2011 at 7:02 PM, Roedel, Joerg <Joerg.Roedel@....com> wrote:
> > I still don't get the need for this. It would make sense to encode
> > different types of faults, like page-faults or interrupt-faults.
> 
> Right.
> 
> > When I read the comment above it sounds more like you want to encode
> > different error-levels, like recoverable and unrecoverable error.
> > The exact meaning of these values need to be clarified.
> 
> Well, we currently only need to say "something bad has happened".
> 
> We don't need at this point to tell whether it's a hardware bug,
> inconsistent data, missing page-table entries or whatnot, because we
> don't expect the user (or the iommu core itself) to do anything about
> it. Not that it's not possible though: a valid response one day would
> be to fix the page-table or add a missing TLB (depending on the mode
> the hardware is configured to) but this is not (yet?) implemented. So
> a "general unrecoverable error" is enough at this point, but it's
> certainly makes sense to allow drivers to provide additional types of
> errors/faults - once they are implemented.

But besides real faults all this can be handled in the iommu-driver
itself, right? So there is no need to communicate other errors than
page-faults up to the driver.

For now I think it is the best to remove this IOMMU_ERROR thing. It is
inherent to the function call already. When a real use-case comes up we
can easily add it later.

	Joerg

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