linux-kernel - Re: [PATCH] intel-iommu: Synchronize gcmd value with global command register

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Message-ID: <20130402140546.GA15687@8bytes.org>
Date:	Tue, 2 Apr 2013 16:05:47 +0200
From:	Joerg Roedel <joro@...tes.org>
To:	Takao Indoh <indou.takao@...fujitsu.com>
Cc:	linux-kernel@...r.kernel.org, iommu@...ts.linux-foundation.org,
	dwmw2@...radead.org, kexec@...ts.infradead.org
Subject: Re: [PATCH] intel-iommu: Synchronize gcmd value with global command
 register

On Mon, Apr 01, 2013 at 02:45:18PM +0900, Takao Indoh wrote:
> <Current flow on kdump boot>
> enable_IR
>   intel_enable_irq_remapping
>     iommu_disable_irq_remapping  <== IRES/QIES/TES disabled here
>     dmar_disable_qi              <== do nothing
>     dmar_enable_qi               <== QIES enabled
>     intel_setup_irq_remapping    <== IRES enabled

But what we want to do here in the kdumo case is to disable translation
too, right? Because the former kernel might have translation and
irq-remapping enabled and the kdump kernel might be compiled without
support for dma-remapping. So if we don't disable translation here too
the kdump kernel is unable to do DMA.

I agree that disabling translation should be a bit more explicit instead
of the current code.


	Joerg


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