linux-kernel - Re: A question about state machine function state

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Message-ID: <20150601111802.GD31271@dhcp-128-28.nay.redhat.com>
Date:	Mon, 1 Jun 2015 19:18:02 +0800
From:	Baoquan He <bhe@...hat.com>
To:	Joerg Roedel <joro@...tes.org>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: A question about state machine function state_next()

On 06/01/15 at 11:21am, Joerg Roedel wrote:
> Hi Baoquan,
> 
> On Mon, Jun 01, 2015 at 05:09:02PM +0800, Baoquan He wrote:
> > Then I am wondering  how amd_iommu_dma_ops is assigned. Maybe I need
> > check all functions more clearly.
> 
> The AMD IOMMU driver only uses per-device dma_ops. They are assigned to
> each device in device_dma_ops_init() at boot and in the
> device_change_notifier() on hotplug events.

Checked the code again, it may be a code bug if this is done in
device_dma_ops_init(). Since this is called in
amd_iommu_init_dma_ops()<-amd_iommu_init_dma(). And amd_iommu_init_dma()
is only called in case IOMMU_INTERRUPTS_EN code block. According to the
code flow if I understand correctly, it can't be here at boot stage.
state_next() will change the state according to the calling times. And
in amd iommu only four times to call iommu_go_to_state, it can't go to
IOMMU_PCI_INIT and the after cases.

I am not sure if my understanding is correct, or I missed something.

Thanks
Baoquan

> 
> 
> > Actually I am investigating how to port Zhenhua's kdump fix for intel
> > iommu to amd iommu since the similar bug happened on systems with amd
> > iommu. If you don't mind I can make these clean up during I understand
> > these iommu codes. And if Zhenhua plan to post patch for amd fix, I
> > can help review and test. Otherwise I can make some research and try
> > to post a draft patch.
> 
> Thanks for looking into this. Unfortunatly this somehow conflicts with
> my recent default-domain patch-set, which moves functionality into the
> IOMMU core and converts the AMD driver to make use of it. I have no real
> idea yet how to make both work, but it shouldn't be too hard. Maybe you can
> have a look into that patch-set too?
> 
> 
> 	Joerg
> 
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