[RFC PATCH 3/4] drm/amdgpu/dma-buf: Pin MMIO_REMAP at export; unpin on release

[Srinivasan Shanmugam]

This keeps MMIO_REMAP fixed for its whole lifetime.
Other buffers (VRAM/GTT) are unchanged.

This change pins it when we export the dma-buf.
If the export fails, we undo the pin.
When the dma-buf is released, we unpin it.

MMIO_REMAP (HDP flush page) is a hardware I/O window, not normal RAM.
It should never be moved

Cc: Christian König <christian.koe...@amd.com>
Cc: Alex Deucher <alexander.deuc...@amd.com>
Signed-off-by: Srinivasan Shanmugam <srinivasan.shanmu...@amd.com>
---
 drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c | 36 +++++++++++++++++++--
 1 file changed, 33 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c 
b/drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c
index f85e16be438f..31d78561ab95 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c
@@ -47,6 +47,7 @@
 #include <linux/scatterlist.h>
 #include <linux/slab.h>
 
+static void amdgpu_dmabuf_release(struct dma_buf *dmabuf);
 static const struct dma_buf_attach_ops amdgpu_dma_buf_attach_ops;
 
 /**
@@ -377,13 +378,27 @@ const struct dma_buf_ops amdgpu_dmabuf_ops = {
        .unpin = amdgpu_dma_buf_unpin,
        .map_dma_buf = amdgpu_dma_buf_map,
        .unmap_dma_buf = amdgpu_dma_buf_unmap,
-       .release = drm_gem_dmabuf_release,
+       .release = amdgpu_dmabuf_release,
        .begin_cpu_access = amdgpu_dma_buf_begin_cpu_access,
        .mmap = drm_gem_dmabuf_mmap,
        .vmap = drm_gem_dmabuf_vmap,
        .vunmap = drm_gem_dmabuf_vunmap,
 };
 
+/* Drop the export-time pin for MMIO_REMAP when the dma-buf is finally 
released. */
+static void amdgpu_dmabuf_release(struct dma_buf *dmabuf)
+{
+       struct drm_gem_object *gobj = dmabuf->priv;
+       struct amdgpu_bo *bo = gem_to_amdgpu_bo(gobj);
+
+       if (bo && bo->tbo.resource &&
+           bo->tbo.resource->mem_type == AMDGPU_PL_MMIO_REMAP)
+               amdgpu_bo_unpin(bo);
+
+       drm_gem_dmabuf_release(dmabuf);
+}
+
+
 /**
  * amdgpu_gem_prime_export - &drm_driver.gem_prime_export implementation
  * @gobj: GEM BO
@@ -399,15 +414,30 @@ struct dma_buf *amdgpu_gem_prime_export(struct 
drm_gem_object *gobj,
 {
        struct amdgpu_bo *bo = gem_to_amdgpu_bo(gobj);
        struct dma_buf *buf;
+       int r;
 
        if (amdgpu_ttm_tt_get_usermm(bo->tbo.ttm) ||
            bo->flags & AMDGPU_GEM_CREATE_VM_ALWAYS_VALID)
                return ERR_PTR(-EPERM);
 
+       /* MMIO_REMAP: opt-in + pin at export so later paths never migrate it */
+       if (bo->tbo.resource &&
+           bo->tbo.resource->mem_type == AMDGPU_PL_MMIO_REMAP) {
+               r = amdgpu_bo_pin(bo, AMDGPU_GEM_DOMAIN_GTT);
+               if (r)
+                       return ERR_PTR(r);
+       }
+
        buf = drm_gem_prime_export(gobj, flags);
-       if (!IS_ERR(buf))
-               buf->ops = &amdgpu_dmabuf_ops;
+       if (IS_ERR(buf)) {
+               /* if export failed, drop the pin we took */
+               if (bo->tbo.resource &&
+                   bo->tbo.resource->mem_type == AMDGPU_PL_MMIO_REMAP)
+                       amdgpu_bo_unpin(bo);
+               return buf;
+       }
 
+       buf->ops = &amdgpu_dmabuf_ops;
        return buf;
 }
 
-- 
2.34.1