From: Thierry Reding treding@nvidia.com
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@nvidia.com --- 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; } }