Refactor the confusing logic to make it both clearer and more robust. If
the host1x parent device does have an IOMMU domain then iommu_present()
is redundantly true, while otherwise for the 32-bit DMA mask case it
still doesn't say whether the IOMMU driver actually knows about the DRM
device or not.
Signed-off-by: Robin Murphy <robin.murphy@xxxxxxx>
---
v2: Fix logic for older SoCs and clarify.
drivers/gpu/drm/tegra/drm.c | 28 ++++++++++++++++++++--------
1 file changed, 20 insertions(+), 8 deletions(-)
diff --git a/drivers/gpu/drm/tegra/drm.c b/drivers/gpu/drm/tegra/drm.c
index 9464f522e257..4f2bdab31064 100644
--- a/drivers/gpu/drm/tegra/drm.c
+++ b/drivers/gpu/drm/tegra/drm.c
@@ -1092,6 +1092,19 @@ static bool host1x_drm_wants_iommu(struct host1x_device *dev)
struct host1x *host1x = dev_get_drvdata(dev->dev.parent);
struct iommu_domain *domain;
+ /* For starters, this is moot if no IOMMU is available */
+ if (!device_iommu_mapped(&dev->dev))
+ return false;
+
+ /*
+ * Tegra20 and Tegra30 don't support addressing memory beyond the
+ * 32-bit boundary, so the regular GATHER opcodes will always be
+ * sufficient and whether or not the host1x is attached to an IOMMU
+ * doesn't matter.
+ */
+ if (host1x_get_dma_mask(host1x) <= DMA_BIT_MASK(32))
+ return true;
+
/*
* If the Tegra DRM clients are backed by an IOMMU, push buffers are
* likely to be allocated beyond the 32-bit boundary if sufficient
@@ -1122,14 +1135,13 @@ static bool host1x_drm_wants_iommu(struct host1x_device *dev)
domain = iommu_get_domain_for_dev(dev->dev.parent);
/*
- * Tegra20 and Tegra30 don't support addressing memory beyond the
- * 32-bit boundary, so the regular GATHER opcodes will always be
- * sufficient and whether or not the host1x is attached to an IOMMU
- * doesn't matter.
+ * At the moment, the exact type of domain doesn't actually matter.
+ * Only for 64-bit kernels might this be a managed DMA API domain, and
+ * then only on newer SoCs using arm-smmu, since tegra-smmu doesn't
+ * support default domains at all, and since those SoCs are the same
+ * ones with extended GATHER support, even if it's a passthrough domain
+ * it can still work out OK.
*/
- if (!domain && host1x_get_dma_mask(host1x) <= DMA_BIT_MASK(32))
- return true;
-
return domain != NULL;
}
@@ -1149,7 +1161,7 @@ static int host1x_drm_probe(struct host1x_device *dev)
goto put;
}
- if (host1x_drm_wants_iommu(dev) && iommu_present(&platform_bus_type)) {
+ if (host1x_drm_wants_iommu(dev)) {
tegra->domain = iommu_domain_alloc(&platform_bus_type);
if (!tegra->domain) {
err = -ENOMEM;
--
2.28.0.dirty
