Messages in this thread Patch in this message | | | Subject | Re: [PATCH v2] iommu/mediatek: Move attach_device after iommu-group is ready for M4Uv1 | From | Robin Murphy <> | Date | Wed, 24 Jan 2018 14:55:38 +0000 |
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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@arm.com> > CC: Honghui Zhang <honghui.zhang@mediatek.com> > Fixes: 05f80300dc8b ("iommu: Finish making iommu_group support mandatory") > Reported-by: Ryder Lee <ryder.lee@mediatek.com> > Tested-by: Bibby Hsieh <bibby.hsieh@mediatek.com> > Signed-off-by: Yong Wu <yong.wu@mediatek.com> > --- > 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;
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