drm/tegra: gem: Don't attach dma-bufs when not needed

The dma-buf import code currently attaches and maps all imported
dma-bufs to the drm device to get their sgt for mapping to the
directly managed IOMMU domain.

In many cases, like for newer chips (Tegra186+), the directly
managed IOMMU domain is, however, not used. Mapping to the drm
device can also cause issues e.g. with swiotlb since it is not
a real device.

To improve the situation, only attach and map imported dma-bufs
when required.

Signed-off-by: Mikko Perttunen <mperttunen@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240424051335.2872574-2-cyndis@kapsi.fi

diff --git a/drivers/gpu/drm/tegra/gem.c b/drivers/gpu/drm/tegra/gem.c
index 189861c6c630b5cc753ed5a8230e64735cf1dc11..d275404ad0e9898fd312a13237f4ccd325ef130e 100644 (file)
--- a/drivers/gpu/drm/tegra/gem.c
+++ b/drivers/gpu/drm/tegra/gem.c
@@ -76,8 +76,8 @@ static struct host1x_bo_mapping *tegra_bo_pin(struct device *dev, struct host1x_
        /*
         * Imported buffers need special treatment to satisfy the semantics of DMA-BUF.
         */
-       if (gem->import_attach) {
-               struct dma_buf *buf = gem->import_attach->dmabuf;
+       if (obj->dma_buf) {
+               struct dma_buf *buf = obj->dma_buf;
 
                map->attach = dma_buf_attach(buf, dev);
                if (IS_ERR(map->attach)) {
@@ -184,8 +184,8 @@ static void *tegra_bo_mmap(struct host1x_bo *bo)
        if (obj->vaddr)
                return obj->vaddr;
 
-       if (obj->gem.import_attach) {
-               ret = dma_buf_vmap_unlocked(obj->gem.import_attach->dmabuf, &map);
+       if (obj->dma_buf) {
+               ret = dma_buf_vmap_unlocked(obj->dma_buf, &map);
                if (ret < 0)
                        return ERR_PTR(ret);
 
@@ -208,8 +208,8 @@ static void tegra_bo_munmap(struct host1x_bo *bo, void *addr)
        if (obj->vaddr)
                return;
 
-       if (obj->gem.import_attach)
-               return dma_buf_vunmap_unlocked(obj->gem.import_attach->dmabuf, &map);
+       if (obj->dma_buf)
+               return dma_buf_vunmap_unlocked(obj->dma_buf, &map);
 
        vunmap(addr);
 }
@@ -465,27 +465,32 @@ static struct tegra_bo *tegra_bo_import(struct drm_device *drm,
        if (IS_ERR(bo))
                return bo;
 
-       attach = dma_buf_attach(buf, drm->dev);
-       if (IS_ERR(attach)) {
-               err = PTR_ERR(attach);
-               goto free;
-       }
-
-       get_dma_buf(buf);
+       /*
+        * If we need to use IOMMU API to map the dma-buf into the internally managed
+        * domain, map it first to the DRM device to get an sgt.
+        */
+       if (tegra->domain) {
+               attach = dma_buf_attach(buf, drm->dev);
+               if (IS_ERR(attach)) {
+                       err = PTR_ERR(attach);
+                       goto free;
+               }
 
-       bo->sgt = dma_buf_map_attachment_unlocked(attach, DMA_TO_DEVICE);
-       if (IS_ERR(bo->sgt)) {
-               err = PTR_ERR(bo->sgt);
-               goto detach;
-       }
+               bo->sgt = dma_buf_map_attachment_unlocked(attach, DMA_TO_DEVICE);
+               if (IS_ERR(bo->sgt)) {
+                       err = PTR_ERR(bo->sgt);
+                       goto detach;
+               }
 
-       if (tegra->domain) {
                err = tegra_bo_iommu_map(tegra, bo);
                if (err < 0)
                        goto detach;
+
+               bo->gem.import_attach = attach;
        }
 
-       bo->gem.import_attach = attach;
+       get_dma_buf(buf);
+       bo->dma_buf = buf;
 
        return bo;
 
@@ -516,20 +521,21 @@ void tegra_bo_free_object(struct drm_gem_object *gem)
                                dev_name(mapping->dev));
        }
 
-       if (tegra->domain)
+       if (tegra->domain) {
                tegra_bo_iommu_unmap(tegra, bo);
 
-       if (gem->import_attach) {
-               struct dma_buf *dmabuf = gem->import_attach->dmabuf;
-
-               dma_buf_unmap_attachment_unlocked(gem->import_attach, bo->sgt,
-                                                 DMA_TO_DEVICE);
-               dma_buf_detach(dmabuf, gem->import_attach);
-               dma_buf_put(dmabuf);
-       } else {
-               tegra_bo_free(gem->dev, bo);
+               if (gem->import_attach) {
+                       dma_buf_unmap_attachment_unlocked(gem->import_attach, bo->sgt,
+                                                         DMA_TO_DEVICE);
+                       dma_buf_detach(gem->import_attach->dmabuf, gem->import_attach);
+               }
        }
 
+       tegra_bo_free(gem->dev, bo);
+
+       if (bo->dma_buf)
+               dma_buf_put(bo->dma_buf);
+
        drm_gem_object_release(gem);
        kfree(bo);
 }

diff --git a/drivers/gpu/drm/tegra/gem.h b/drivers/gpu/drm/tegra/gem.h
index cb5146a67668336276219d340424cad66726195c..bf2cbd48eb3f672dfd707c2099c268db7f85cf18 100644 (file)
--- a/drivers/gpu/drm/tegra/gem.h
+++ b/drivers/gpu/drm/tegra/gem.h
@@ -32,6 +32,26 @@ struct tegra_bo_tiling {
        enum tegra_bo_sector_layout sector_layout;
 };
 
+/*
+ * How memory is referenced within a tegra_bo:
+ *
+ * Buffer source  | Mapping API(*)  | Fields
+ * ---------------+-----------------+---------------
+ * Allocated here | DMA API         | iova (IOVA mapped to drm->dev), vaddr (CPU VA)
+ *
+ * Allocated here | IOMMU API       | pages/num_pages (Phys. memory), sgt (Mapped to drm->dev),
+ *                                  | iova/size (Mapped to domain)
+ *
+ * Imported       | DMA API         | dma_buf (Imported dma_buf)
+ *
+ * Imported       | IOMMU API       | dma_buf (Imported dma_buf),
+ *                                  | gem->import_attach (Attachment on drm->dev),
+ *                                  | sgt (Mapped to drm->dev)
+ *                                  | iova/size (Mapped to domain)
+ *
+ * (*) If tegra->domain is set, i.e. TegraDRM IOMMU domain is directly managed through IOMMU API,
+ *     this is IOMMU API. Otherwise DMA API.
+ */
 struct tegra_bo {
        struct drm_gem_object gem;
        struct host1x_bo base;
@@ -39,6 +59,7 @@ struct tegra_bo {
        struct sg_table *sgt;
        dma_addr_t iova;
        void *vaddr;
+       struct dma_buf *dma_buf;
 
        struct drm_mm_node *mm;
        unsigned long num_pages;