Re: [PATCH v2] iommu/mediatek: Move attach_device after iommu-group is ready for M4Uv1
From: Robin Murphy
Date: Wed Jan 24 2018 - 09:55:48 EST
On 23/01/18 08:39, Yong Wu wrote:
In the commit 05f80300dc8b ("iommu: Finish making iommu_group support
mandatory"), the iommu framework has supposed all the iommu drivers have
their owner iommu-group, it get rid of the FIXME workarounds while the
group is NULL. But the flow of Mediatek M4U gen1 looks a bit trick that
it will hang at this case:
==========================================
Unable to handle kernel NULL pointer dereference at virtual address 00000030
PC is at mutex_lock+0x28/0x54
LR is at iommu_attach_device+0xa4/0xd4
pc : [<c07632e8>] lr : [<c04736fc>] psr: 60000013
sp : df0edbb8 ip : df0edbc8 fp : df0edbc4
r10: c114da14 r9 : df2a3e40 r8 : 00000003
r7 : df27a210 r6 : df2a90c4 r5 : 00000030 r4 : 00000000
r3 : df0f8000 r2 : fffff000 r1 : df29c610 r0 : 00000030
Flags: nZCv IRQs on FIQs on Mode SVC_32 ISA ARM Segment none
xxx
(mutex_lock) from [<c04736fc>] (iommu_attach_device+0xa4/0xd4)
(iommu_attach_device) from [<c011b9dc>] (__arm_iommu_attach_device+0x28/0x90)
(__arm_iommu_attach_device) from [<c011ba60>] (arm_iommu_attach_device+0x1c/0x30)
(arm_iommu_attach_device) from [<c04759ac>] (mtk_iommu_add_device+0xfc/0x214)
(mtk_iommu_add_device) from [<c0472aa4>] (add_iommu_group+0x3c/0x68)
(add_iommu_group) from [<c047d044>] (bus_for_each_dev+0x78/0xac)
(bus_for_each_dev) from [<c04734a4>] (bus_set_iommu+0xb0/0xec)
(bus_set_iommu) from [<c0476310>] (mtk_iommu_probe+0x328/0x368)
(mtk_iommu_probe) from [<c048189c>] (platform_drv_probe+0x5c/0xc0)
(platform_drv_probe) from [<c047f510>] (driver_probe_device+0x2f4/0x4d8)
(driver_probe_device) from [<c047f800>] (__driver_attach+0x10c/0x128)
(__driver_attach) from [<c047d044>] (bus_for_each_dev+0x78/0xac)
(bus_for_each_dev) from [<c047ec78>] (driver_attach+0x2c/0x30)
(driver_attach) from [<c047e640>] (bus_add_driver+0x1e0/0x278)
(bus_add_driver) from [<c048052c>] (driver_register+0x88/0x108)
(driver_register) from [<c04817ec>] (__platform_driver_register+0x50/0x58)
(__platform_driver_register) from [<c0b31380>] (m4u_init+0x24/0x28)
(m4u_init) from [<c0101c38>] (do_one_initcall+0xf0/0x17c)
=========================
The root cause is that "arm_iommu_attach_device" is called before
"iommu_group_get_for_dev" in the interface "mtk_iommu_add_device". Thus,
We adjust the sequence of this two functions.
Unfortunately, there is another issue after the solution above, From the
function "iommu_attach_device", Only one device in each a iommu group is
allowed. In Mediatek case, there is only one m4u group, all the devices
are in one group. thus it get fail at this step.
In order to satisfy this requirement, a new iommu group is allocated for
each a iommu consumer device. But meanwhile, we still have to use the
same domain for all the iommu group. Use a global variable "mtk_domain_v1"
to save the global domain.
Argh, sorry for breaking it! Seems I managed to forget just how horrible
and fiddly all the arm_iommu_* stuff is :(
CC: Robin Murphy <robin.murphy@xxxxxxx>
CC: Honghui Zhang <honghui.zhang@xxxxxxxxxxxx>
Fixes: 05f80300dc8b ("iommu: Finish making iommu_group support mandatory")
Reported-by: Ryder Lee <ryder.lee@xxxxxxxxxxxx>
Tested-by: Bibby Hsieh <bibby.hsieh@xxxxxxxxxxxx>
Signed-off-by: Yong Wu <yong.wu@xxxxxxxxxxxx>
---
changes since v1:
Add mtk_domain_v1=NULL in domain_free for symmetry.
v1: https://patchwork.kernel.org/patch/10176255/
---
drivers/iommu/mtk_iommu_v1.c | 42 +++++++++++++++++++-----------------------
1 file changed, 19 insertions(+), 23 deletions(-)
diff --git a/drivers/iommu/mtk_iommu_v1.c b/drivers/iommu/mtk_iommu_v1.c
index 542930c..86106bf 100644
--- a/drivers/iommu/mtk_iommu_v1.c
+++ b/drivers/iommu/mtk_iommu_v1.c
@@ -103,6 +103,9 @@ struct mtk_iommu_domain {
struct mtk_iommu_data *data;
};
+/* There is only a iommu domain in M4U gen1. */
+static struct mtk_iommu_domain *mtk_domain_v1;
+
static struct mtk_iommu_domain *to_mtk_domain(struct iommu_domain *dom)
{
return container_of(dom, struct mtk_iommu_domain, domain);
@@ -251,10 +254,15 @@ static struct iommu_domain *mtk_iommu_domain_alloc(unsigned type)
if (type != IOMMU_DOMAIN_UNMANAGED)
return NULL;
+ /* Always return the same domain. */
+ if (mtk_domain_v1)
+ return &mtk_domain_v1->domain;
This seems a bit too fragile (and I vaguely recall we may have discussed
and rejected this approach for the original driver), since any code doing:
unused = iommu_domain_alloc(bus);
iommu_domain_free(unused);
will pull the rug out from under everyone's feet in a very nasty and
unexpected manner. Given that mtk_iommu_create_mapping() is already a
giant workaround for the ARM DMA code not understanding groups and
default domains, I'd prefer not to have to regress "correct" driver
behaviour for the sake of that; how about something like the below diff,
is that enough to make things work?
Robin.
----->8-----
diff --git a/drivers/iommu/mtk_iommu_v1.c b/drivers/iommu/mtk_iommu_v1.c
index 542930cd183d..8b90b7a72238 100644
--- a/drivers/iommu/mtk_iommu_v1.c
+++ b/drivers/iommu/mtk_iommu_v1.c
@@ -376,6 +376,7 @@ static int mtk_iommu_create_mapping(struct device *dev,
struct platform_device *m4updev;
struct dma_iommu_mapping *mtk_mapping;
struct device *m4udev;
+ struct iommu_group *group;
int ret;
if (args->args_count != 1) {
@@ -418,6 +419,22 @@ static int mtk_iommu_create_mapping(struct device *dev,
m4udev->archdata.iommu = mtk_mapping;
}
+ /*
+ * This is a short-term bodge because the ARM DMA code doesn't
+ * understand multi-device groups, but we have to call into it
+ * successfully (and not just rely on a normal IOMMU API attach
+ * here) in order to set the correct DMA API ops on @dev.
+ */
+ group = iommu_group_alloc();
+ if (IS_ERR(group)) {
+ ret = ERR_PTR(group);
+ goto err_release_mapping;
+ }
+ ret = iommu_group_add_device(group, dev);
+ iommu_group_put(group);
+ if (ret)
+ goto err_release_mapping;
+
ret = arm_iommu_attach_device(dev, mtk_mapping);
if (ret)
goto err_release_mapping;