From: Thierry Reding <treding@xxxxxxxxxx>
If a client is already attached to an IOMMU domain that is not the
shared domain, don't try to attach it again. This allows using the
IOMMU-backed DMA API.
Since the IOMMU-backed DMA API is now supported and there's no way
to detach from it on 64-bit ARM, don't bother to detach from it on
32-bit ARM either.
Signed-off-by: Thierry Reding <treding@xxxxxxxxxx>
---
drivers/gpu/drm/tegra/drm.c | 66 +++++++++++++++++++++++++++----------
drivers/gpu/drm/tegra/drm.h | 1 +
2 files changed, 49 insertions(+), 18 deletions(-)
diff --git a/drivers/gpu/drm/tegra/drm.c b/drivers/gpu/drm/tegra/drm.c
index efc8a27b9e6a..56e5e7a5c108 100644
--- a/drivers/gpu/drm/tegra/drm.c
+++ b/drivers/gpu/drm/tegra/drm.c
@@ -20,10 +20,6 @@
#include <drm/drm_prime.h>
#include <drm/drm_vblank.h>
-#if IS_ENABLED(CONFIG_ARM_DMA_USE_IOMMU)
-#include <asm/dma-iommu.h>
-#endif
-
#include "drm.h"
#include "gem.h"
@@ -908,30 +904,27 @@ int tegra_drm_unregister_client(struct tegra_drm *tegra,
int host1x_client_iommu_attach(struct host1x_client *client)
{
+ struct iommu_domain *domain = iommu_get_domain_for_dev(client->dev);
struct drm_device *drm = dev_get_drvdata(client->parent);
struct tegra_drm *tegra = drm->dev_private;
struct iommu_group *group = NULL;
int err;
- if (tegra->domain) {
- struct iommu_domain *domain;
+ /*
+ * If the host1x client is already attached to an IOMMU domain that is
+ * not the shared IOMMU domain, don't try to attach it to a different
+ * domain. This allows using the IOMMU-backed DMA API.
+ */
+ if (domain && domain != tegra->domain)
+ return 0;
+ if (tegra->domain) {
group = iommu_group_get(client->dev);
if (!group) {
dev_err(client->dev, "failed to get IOMMU group\n");
return -ENODEV;
}
-#if IS_ENABLED(CONFIG_ARM_DMA_USE_IOMMU)
- if (client->dev->archdata.mapping) {
- struct dma_iommu_mapping *mapping =
- to_dma_iommu_mapping(client->dev);
- arm_iommu_detach_device(client->dev);
- arm_iommu_release_mapping(mapping);
- }
-#endif
-
- domain = iommu_get_domain_for_dev(client->dev);
if (domain != tegra->domain) {
err = iommu_attach_group(tegra->domain, group);
if (err < 0) {
@@ -939,6 +932,8 @@ int host1x_client_iommu_attach(struct host1x_client *client)
return err;
}
}
+
+ tegra->use_explicit_iommu = true;
}
client->group = group;
@@ -963,6 +958,7 @@ void host1x_client_iommu_detach(struct host1x_client *client)
iommu_detach_group(tegra->domain, client->group);
iommu_group_put(client->group);
+ client->group = NULL;
}
}
@@ -1046,6 +1042,7 @@ void tegra_drm_free(struct tegra_drm *tegra, size_t size, void *virt,
static int host1x_drm_probe(struct host1x_device *dev)
{
struct drm_driver *driver = &tegra_drm_driver;
+ struct iommu_domain *domain;
struct tegra_drm *tegra;
struct drm_device *drm;
int err;
@@ -1060,7 +1057,36 @@ static int host1x_drm_probe(struct host1x_device *dev)
goto put;
}
- if (iommu_present(&platform_bus_type)) {
+ /*
+ * If the Tegra DRM clients are backed by an IOMMU, push buffers are
+ * likely to be allocated beyond the 32-bit boundary if sufficient
+ * system memory is available. This is problematic on earlier Tegra
+ * generations where host1x supports a maximum of 32 address bits in
+ * the GATHER opcode. In this case, unless host1x is behind an IOMMU
+ * as well it won't be able to process buffers allocated beyond the
+ * 32-bit boundary.
+ *
+ * The DMA API will use bounce buffers in this case, so that could
+ * perhaps still be made to work, even if less efficient, but there
+ * is another catch: in order to perform cache maintenance on pages
+ * allocated for discontiguous buffers we need to map and unmap the
+ * SG table representing these buffers. This is fine for something
+ * small like a push buffer, but it exhausts the bounce buffer pool
+ * (typically on the order of a few MiB) for framebuffers (many MiB
+ * for any modern resolution).
+ *
+ * Work around this by making sure that Tegra DRM clients only use
+ * an IOMMU if the parent host1x also uses an IOMMU.
+ *
+ * Note that there's still a small gap here that we don't cover: if
+ * the DMA API is backed by an IOMMU there's no way to control which
+ * device is attached to an IOMMU and which isn't, except via wiring
+ * up the device tree appropriately. This is considered an problem
+ * of integration, so care must be taken for the DT to be consistent.
+ */
+ domain = iommu_get_domain_for_dev(drm->dev->parent);
+
+ if (domain && iommu_present(&platform_bus_type)) {
tegra->domain = iommu_domain_alloc(&platform_bus_type);
if (!tegra->domain) {
err = -ENOMEM;
@@ -1104,7 +1130,7 @@ static int host1x_drm_probe(struct host1x_device *dev)
if (err < 0)
goto fbdev;
- if (tegra->domain) {
+ if (tegra->use_explicit_iommu) {
u64 carveout_start, carveout_end, gem_start, gem_end;
u64 dma_mask = dma_get_mask(&dev->dev);
dma_addr_t start, end;
@@ -1132,6 +1158,10 @@ static int host1x_drm_probe(struct host1x_device *dev)
DRM_DEBUG_DRIVER(" GEM: %#llx-%#llx\n", gem_start, gem_end);
DRM_DEBUG_DRIVER(" Carveout: %#llx-%#llx\n", carveout_start,
carveout_end);
+ } else if (tegra->domain) {
+ iommu_domain_free(tegra->domain);
+ tegra->domain = NULL;
+ iova_cache_put();
}
if (tegra->hub) {
diff --git a/drivers/gpu/drm/tegra/drm.h b/drivers/gpu/drm/tegra/drm.h
index 28f2820a7371..d941553f7a3d 100644
--- a/drivers/gpu/drm/tegra/drm.h
+++ b/drivers/gpu/drm/tegra/drm.h
@@ -36,6 +36,7 @@ struct tegra_drm {
struct drm_device *drm;
struct iommu_domain *domain;
+ bool use_explicit_iommu;
struct mutex mm_lock;
struct drm_mm mm;
--
2.23.0
