drm/panthor: Avoid adding of kernel BOs to extobj list

[ Upstream commit ce04ec03a9c2c4f3e60e26f21311b25d5a478208 ]

The kernel BOs unnecessarily got added to the external objects list
of drm_gpuvm, when mapping to GPU, which would have resulted in few
extra CPU cycles being spent at the time of job submission as
drm_exec_until_all_locked() loop iterates over all external objects.

Kernel BOs are private to a VM and so they share the dma_resv object of
the dummy GEM object created for a VM. Use of DRM_EXEC_IGNORE_DUPLICATES
flag ensured the recursive locking of the dummy GEM object was ignored.
Also no extra space got allocated to add fences to the dma_resv object
of dummy GEM object. So no other impact apart from few extra CPU cycles.

This commit sets the pointer to dma_resv object of GEM object of
kernel BOs before they are mapped to GPU, to prevent them from
being added to external objects list.

v2: Add R-bs and fixes tags

Fixes: 8a1cc07578bf ("drm/panthor: Add GEM logical block")
Signed-off-by: Akash Goel <akash.goel@arm.com>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Steven Price <steven.price@arm.com>
Link: https://patch.msgid.link/20251120172118.2741724-1-akash.goel@arm.com
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/drivers/gpu/drm/panthor/panthor_gem.c b/drivers/gpu/drm/panthor/panthor_gem.c
index 8387a075150bd1b95073cc28334c3ce4215185b1..0438b80a6434b421e83172c598dd3516daa93e97 100644 (file)
--- a/drivers/gpu/drm/panthor/panthor_gem.c
+++ b/drivers/gpu/drm/panthor/panthor_gem.c
@@ -88,6 +88,9 @@ panthor_kernel_bo_create(struct panthor_device *ptdev, struct panthor_vm *vm,
        bo = to_panthor_bo(&obj->base);
        kbo->obj = &obj->base;
        bo->flags = bo_flags;
+       bo->exclusive_vm_root_gem = panthor_vm_root_gem(vm);
+       drm_gem_object_get(bo->exclusive_vm_root_gem);
+       bo->base.base.resv = bo->exclusive_vm_root_gem->resv;
 
        /* The system and GPU MMU page size might differ, which becomes a
         * problem for FW sections that need to be mapped at explicit address
@@ -105,9 +108,6 @@ panthor_kernel_bo_create(struct panthor_device *ptdev, struct panthor_vm *vm,
                goto err_free_va;
 
        kbo->vm = panthor_vm_get(vm);
-       bo->exclusive_vm_root_gem = panthor_vm_root_gem(vm);
-       drm_gem_object_get(bo->exclusive_vm_root_gem);
-       bo->base.base.resv = bo->exclusive_vm_root_gem->resv;
        return kbo;
 
 err_free_va: