Re: [PATCH v2] iommu/mediatek: Move attach_device after iommu-group is ready for M4Uv1

[Robin Murphy <robin.murphy@arm.com>]

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;