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 | 55 +++++++++++++++++++++++++++----------
1 file changed, 41 insertions(+), 14 deletions(-)
diff --git a/drivers/gpu/drm/tegra/drm.c b/drivers/gpu/drm/tegra/drm.c
index 959086644b52..3012f13bab97 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"
@@ -89,6 +85,7 @@ tegra_drm_mode_config_helpers = {
static int tegra_drm_load(struct drm_device *drm, unsigned long flags)
{
struct host1x_device *device = to_host1x_device(drm->dev);
+ struct iommu_domain *domain;
struct tegra_drm *tegra;
int err;
@@ -96,7 +93,36 @@ static int tegra_drm_load(struct drm_device *drm, unsigned long flags)
if (!tegra)
return -ENOMEM;
- 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;
@@ -139,7 +165,7 @@ static int tegra_drm_load(struct drm_device *drm, unsigned long flags)
if (err < 0)
goto fbdev;
- if (tegra->domain) {
+ if (tegra->group) {
u64 carveout_start, carveout_end, gem_start, gem_end;
u64 dma_mask = dma_get_mask(&device->dev);
dma_addr_t start, end;
@@ -167,6 +193,10 @@ static int tegra_drm_load(struct drm_device *drm, unsigned long flags)
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) {
@@ -1072,11 +1102,15 @@ int tegra_drm_unregister_client(struct tegra_drm *tegra,
int host1x_client_iommu_attach(struct host1x_client *client, bool shared)
{
+ 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 (domain && domain != tegra->domain)
+ return 0;
+
if (tegra->domain) {
group = iommu_group_get(client->dev);
if (!group) {
@@ -1085,14 +1119,6 @@ int host1x_client_iommu_attach(struct host1x_client *client, bool shared)
}
if (!shared || (shared && (group != tegra->group))) {
-#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
err = iommu_attach_group(tegra->domain, group);
if (err < 0) {
iommu_group_put(group);
@@ -1121,6 +1147,7 @@ void host1x_client_iommu_detach(struct host1x_client *client)
}
iommu_group_put(client->group);
+ client->group = NULL;
}
}
--
2.23.0
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