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Subject: Re: [PATCH 0/8] iommu: Make core iommu-groups code more generic
From: Yong Wu <yong.wu@mediatek.com>
To: Joerg Roedel <joro@8bytes.org>
CC: <iommu@lists.linux-foundation.org>, Will Deacon <will.deacon@arm.com>,
        <linux-kernel@vger.kernel.org>, <yingjoe.chen@mediatek.com>,
        <srv_heupstream@mediatek.com>, Daniel Kurtz <djkurtz@google.com>,
        Tomasz Figa <tfiga@google.com>, <eddie.huang@mediatek.com>,
        Matthias Brugger <matthias.bgg@gmail.com>
Date: Tue, 1 Dec 2015 19:29:51 +0800
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On Thu, 2015-11-19 at 14:41 +0100, Joerg Roedel wrote:
> Hi Yong Wu,
> 
> On Thu, Nov 19, 2015 at 04:13:21PM +0800, Yong Wu wrote:
> > (151119_13:39:37.472)WARNING:
> > at /proj/mtk40525/upstreamdev/v4.4/kernel/mediatek/drivers/iommu/iommu.c:1154
> > (151119_13:39:37.472)Modules linked in:
> > (151119_13:39:37.472)CPU: 1 PID: 731 Comm: sh Not tainted 4.4.0-rc1+
> > #37
> > (151119_13:39:37.472)Hardware name: MediaTek MT8173 evaluation board
> > (DT)
> > (151119_13:39:37.472)task: ffffffc076bb4d00 ti: ffffffc076bdc000
> > task.ti: ffffffc076bdc000
> > (151119_13:39:37.472)PC is at iommu_detach_device+0x5c/0xb0
> > (151119_13:39:37.472)LR is at iommu_detach_device+0x30/0xb0
> > xxx
> 
> This warning triggers when you use iommu_detach_device() with a device
> that is in a group with other devices. For those devices you must
> attach/detach the whole group of devices.
> 
> For that you have to use iommu_detach_group() and iommu_attach_group().
> 
> 
> 	Joerg
> 

     Currently We have to use iommu_detach_group and iommu_attach_group.
Is there any plan for adding detach/attach the device within a iommu
group?

Why I ask this is because that:

    There are 2 interfaces in MTK-SMI patch, named by
mtk_smi_larb_get/mtk_smi_larb_put which help enable/disable the
power-domain and clocks for each a device(local arbiter).
Take a example, VIDEO have to call mtk_smi_larb_get to enable its power
and clocks before it works and call mtk_smi_larb_put to disable them
after it work done.

    If the iommu support attach/detach the device in a iommu-group, then
we could request VIDEO to call iommu_attach_device before it works(the
mtk_iommu_attach_device will call the smi interface to enable its power,
clocks and enable iommu).and call iommu_detach_device after it work
done. then the VIDEO could call iommu_attach_device/iommu_detach_device
instead of talking with SMI directly.