[PATCH v7 2/3] iommu/tegra-smmu: Rework tegra_smmu_probe_device()

Nicolin Chen
2020-10-09T16:26:57Z

The bus_set_iommu() in tegra_smmu_probe() enumerates all clients
to call in tegra_smmu_probe_device() where each client searches
its DT node for smmu pointer and swgroup ID, so as to configure
an fwspec. But this requires a valid smmu pointer even before mc
and smmu drivers are probed. So in tegra_smmu_probe() we added a
line of code to fill mc->smmu, marking "a bit of a hack".

This works for most of clients in the DTB, however, doesn't work
for a client that doesn't exist in DTB, a PCI device for example.

Actually, if we return ERR_PTR(-ENODEV) in ->probe_device() when
it's called from bus_set_iommu(), iommu core will let everything
carry on. Then when a client gets probed, of_iommu_configure() in
iommu core will search DTB for swgroup ID and call ->of_xlate()
to prepare an fwspec, similar to tegra_smmu_probe_device() and
tegra_smmu_configure(). Then it'll call tegra_smmu_probe_device()
again, and this time we shall return smmu->iommu pointer properly.

So we can get rid of tegra_smmu_find() and tegra_smmu_configure()
along with DT polling code by letting the iommu core handle every
thing, except a problem that we search iommus property in DTB not
only for swgroup ID but also for mc node to get mc->smmu pointer
to call dev_iommu_priv_set() and return the smmu->iommu pointer.
So we'll need to find another way to get smmu pointer.

Referencing the implementation of sun50i-iommu driver, of_xlate()
has client's dev pointer, mc node and swgroup ID. This means that
we can call dev_iommu_priv_set() in of_xlate() instead, so we can
simply get smmu pointer in ->probe_device().

This patch reworks tegra_smmu_probe_device() by:
1) Removing mc->smmu hack in tegra_smmu_probe() so as to return
ERR_PTR(-ENODEV) in tegra_smmu_probe_device() during stage of
tegra_smmu_probe/tegra_mc_probe().
2) Moving dev_iommu_priv_set() to of_xlate() so we can get smmu
pointer in tegra_smmu_probe_device() to replace DTB polling.
3) Removing tegra_smmu_configure() accordingly since iommu core
takes care of it.

This also fixes a problem that previously we could add clients to
iommu groups before iommu core initializes its default domain:
ubuntu@jetson:~$ dmesg | grep iommu
platform 50000000.host1x: Adding to iommu group 1
platform 57000000.gpu: Adding to iommu group 2
iommu: Default domain type: Translated
platform 54200000.dc: Adding to iommu group 3
platform 54240000.dc: Adding to iommu group 3
platform 54340000.vic: Adding to iommu group 4

Though it works fine with IOMMU_DOMAIN_UNMANAGED, but will have
warnings if switching to IOMMU_DOMAIN_DMA:
iommu: Failed to allocate default IOMMU domain of type 0 for
group (null) - Falling back to IOMMU_DOMAIN_DMA
iommu: Failed to allocate default IOMMU domain of type 0 for
group (null) - Falling back to IOMMU_DOMAIN_DMA

Now, bypassing the first probe_device() call from bus_set_iommu()
fixes the sequence:
ubuntu@jetson:~$ dmesg | grep iommu
iommu: Default domain type: Translated
tegra-host1x 50000000.host1x: Adding to iommu group 0
tegra-dc 54200000.dc: Adding to iommu group 1
tegra-dc 54240000.dc: Adding to iommu group 1
tegra-vic 54340000.vic: Adding to iommu group 2
nouveau 57000000.gpu: Adding to iommu group 3

Note that dmesg log above is testing with IOMMU_DOMAIN_UNMANAGED.

Reviewed-by: Dmitry Osipenko <digetx@gmail.com>
Tested-by: Dmitry Osipenko <digetx@gmail.com>
Signed-off-by: Nicolin Chen <nicoleotsuka@gmail.com>
---

Changelog
v6->v7
* Added comments for put_device(), suggested by Thierry.
v5->v6
* Dropped NULL mc/smmu pointer check, suggested by Dmitry.
* Updated commit message with test results with vanilla DTB.
* Added Dmitry's Reviewed-by and Tested-by.
v4->v5
* Replaced of_node_put() with put_device() in of_xlate().
* Added test result in commit message.
v3->v4
* Moved dev_iommu_priv_set() to of_xlate() so we don't need
to poll DTB for smmu pointer.
* Removed the hack in tegra_smmu_probe() by returning ERR_PTR(
-ENODEV) in tegra_smmu_probe_device() to let iommu core call
in again.
* Removed tegra_smmu_find() and tegra_smmu_configure() as iommu
core takes care of fwspec.
v2->v3
* Used devm_tegra_get_memory_controller() to get mc pointer
* Replaced IS_ERR_OR_NULL with IS_ERR in .probe_device()
v1->v2
* Replaced in .probe_device() tegra_smmu_find/tegra_smmu_configure()
with tegra_get_memory_controller call.
* Dropped the hack in tegra_smmu_probe().

drivers/iommu/tegra-smmu.c | 96 ++++++--------------------------------
1 file changed, 15 insertions(+), 81 deletions(-)

diff --git a/drivers/iommu/tegra-smmu.c b/drivers/iommu/tegra-smmu.c
index 297d49f3f80e..be29f5977145 100644
--- a/drivers/iommu/tegra-smmu.c
+++ b/drivers/iommu/tegra-smmu.c
@@ -797,75 +797,9 @@ static phys_addr_t tegra_smmu_iova_to_phys(struct iommu_domain *domain,
return SMMU_PFN_PHYS(pfn) + SMMU_OFFSET_IN_PAGE(iova);
}

-static struct tegra_smmu *tegra_smmu_find(struct device_node *np)
-{
- struct platform_device *pdev;
- struct tegra_mc *mc;
-
- pdev = of_find_device_by_node(np);
- if (!pdev)
- return NULL;
-
- mc = platform_get_drvdata(pdev);
- if (!mc)
- return NULL;
-
- return mc->smmu;
-}
-
-static int tegra_smmu_configure(struct tegra_smmu *smmu, struct device *dev,
- struct of_phandle_args *args)
-{
- const struct iommu_ops *ops = smmu->iommu.ops;
- int err;
-
- err = iommu_fwspec_init(dev, &dev->of_node->fwnode, ops);
- if (err < 0) {
- dev_err(dev, "failed to initialize fwspec: %d\n", err);
- return err;
- }
-
- err = ops->of_xlate(dev, args);
- if (err < 0) {
- dev_err(dev, "failed to parse SW group ID: %d\n", err);
- iommu_fwspec_free(dev);
- return err;
- }
-
- return 0;
-}
-
static struct iommu_device *tegra_smmu_probe_device(struct device *dev)
{
- struct device_node *np = dev->of_node;
- struct tegra_smmu *smmu = NULL;
- struct of_phandle_args args;
- unsigned int index = 0;
- int err;
-
- while (of_parse_phandle_with_args(np, "iommus", "#iommu-cells", index,
- &args) == 0) {
- smmu = tegra_smmu_find(args.np);
- if (smmu) {
- err = tegra_smmu_configure(smmu, dev, &args);
- of_node_put(args.np);
-
- if (err < 0)
- return ERR_PTR(err);
-
- /*
- * Only a single IOMMU master interface is currently
- * supported by the Linux kernel, so abort after the
- * first match.
- */
- dev_iommu_priv_set(dev, smmu);
-
- break;
- }
-
- of_node_put(args.np);
- index++;
- }
+ struct tegra_smmu *smmu = dev_iommu_priv_get(dev);

if (!smmu)
return ERR_PTR(-ENODEV);
@@ -873,10 +807,7 @@ static struct iommu_device *tegra_smmu_probe_device(struct device *dev)
return &smmu->iommu;
}

-static void tegra_smmu_release_device(struct device *dev)
-{
- dev_iommu_priv_set(dev, NULL);
-}
+static void tegra_smmu_release_device(struct device *dev) {}

static const struct tegra_smmu_group_soc *
tegra_smmu_find_group(struct tegra_smmu *smmu, unsigned int swgroup)
@@ -953,8 +884,21 @@ static struct iommu_group *tegra_smmu_device_group(struct device *dev)
static int tegra_smmu_of_xlate(struct device *dev,
struct of_phandle_args *args)
{
+ struct platform_device *iommu_pdev = of_find_device_by_node(args->np);
+ struct tegra_mc *mc = platform_get_drvdata(iommu_pdev);
u32 id = args->args[0];

+ /*
+ * Note: we are here releasing the reference of &iommu_pdev->dev, which
+ * is mc->dev. Although some functions in tegra_smmu_ops may keep using
+ * its private data beyond this point, it's still safe to do so because
+ * the SMMU parent device is the same as the MC, so the reference count
+ * isn't strictly necessary.
+ */
+ put_device(&iommu_pdev->dev);
+
+ dev_iommu_priv_set(dev, mc->smmu);
+
return iommu_fwspec_add_ids(dev, &id, 1);
}

@@ -1079,16 +1023,6 @@ struct tegra_smmu *tegra_smmu_probe(struct device *dev,
if (!smmu)
return ERR_PTR(-ENOMEM);

- /*
- * This is a bit of a hack. Ideally we'd want to simply return this
- * value. However the IOMMU registration process will attempt to add
- * all devices to the IOMMU when bus_set_iommu() is called. In order
- * not to rely on global variables to track the IOMMU instance, we
- * set it here so that it can be looked up from the .probe_device()
- * callback via the IOMMU device's .drvdata field.
- */
- mc->smmu = smmu;
-
size = BITS_TO_LONGS(soc->num_asids) * sizeof(long);

smmu->asids = devm_kzalloc(dev, size, GFP_KERNEL);
--
2.17.1