Re: [PATCH 0/8] iommu: Make core iommu-groups code more generic

From: Yong Wu
Date: Thu Nov 19 2015 - 04:06:50 EST

On Wed, 2015-10-21 at 23:51 +0200, Joerg Roedel wrote:
> Hi,
> this patch-set makes the core code for managing iommu-groups
> more generic by lifting its dependencies on PCI. The core
> function iommu_group_get_for_dev() had a hard dev_is_pci()
> check in it, followed by PCI specific handling.
> This check is removed in favour of the the revived
> device_group() iommu-ops call-back. With this call-back an
> IOMMU driver can define how the devices it manages are
> grouped together. Two functions, one generic and one for PCI
> devices, are provided that can be uses as a device_group()
> call-back or might be used in such a call-back.
> The existing drivers making use of the iommu_group_get_for_dev()
> function are converted to this call-back.
> Joerg
(Resend since some mail servers reject this.)

Hi Joerg,
Thanks for this patch-set. With this patch-set we can implement our
owner device_group(), then we could achieve all the iommu devices into
the same m4u iommu-group easily.

This patch-set have been merged into v4.4-rc1 where I will get a
WARN while I test iommu_detach_device, below is the warning log:

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+
(151119_13:39:37.472)Hardware name: MediaTek MT8173 evaluation board
(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

>From the code, there are 2 places confuse me:
1. It seems that the iommu core has supposed that there is only one
device in each a group. In the iommu_detach_device/iommu_attach_device
there is a checking like this:

if (iommu_group_device_count(group) != 1) {
goto out_unlock;

Then for our case(there are many devices in a group), Could we delete
this checking?

2. iommu_detach_device will call __iommu_detach_group in which it will
return directly if group->iommu==group->default_iommu, Unfortunately
both will be the same if we call iommu_group_get_for_dev(). then
iommu_detach_device cann't finish the detach operation.
And if there are many devices in a group, It seems that we can not
detach whole the group in the iommu_detach_device.

/* ============================= */
Below is our add_device() and device_group(), if we call the wrong iommu
interface, please also tell me. Thanks.

static int mtk_iommu_add_device(struct device *dev)
struct iommu_group *group;

if (!dev->archdata.iommu) /* Not a iommu client device */
return -ENODEV;

group = iommu_group_get_for_dev(dev);
if (IS_ERR(group))
return PTR_ERR(group);

return 0;

static struct iommu_group *mtk_iommu_device_group(struct device *dev)
struct mtk_iommu_data *data;
struct mtk_iommu_client_priv *priv;

priv = dev->archdata.iommu;
if (!priv)
return ERR_PTR(-ENODEV);

/* All the client devices are in the same m4u iommu-group */
data = dev_get_drvdata(priv->m4udev);
if (!data->m4ugroup) {
data->m4ugroup = iommu_group_alloc();
if (IS_ERR(data->m4ugroup))
dev_err(dev, "Failed to allocate M4U IOMMU group
return data->m4ugroup;
/* ============================= */

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