drm/panthor: Introduce BO labeling

Add a new character string Panthor BO field, and a function that allows
setting it from within the driver.

Driver takes care of freeing the string when it's replaced or no longer
needed at object destruction time, but allocating it is the responsibility
of callers.

Signed-off-by: Adrián Larumbe <adrian.larumbe@collabora.com>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Liviu Dudau <liviu.dudau@arm.com>
Reviewed-by: Steven Price <steven.price@arm.com>
Link: https://lore.kernel.org/r/20250423021238.1639175-2-adrian.larumbe@collabora.com
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>

2 files changed, 63 insertions, 0 deletions

diff --git a/drivers/gpu/drm/panthor/panthor_gem.c b/drivers/gpu/drm/panthor/panthor_gem.c
index 22d78cef9c66..4c9d52378d1c 100644
--- a/drivers/gpu/drm/panthor/panthor_gem.c
+++ b/drivers/gpu/drm/panthor/panthor_gem.c
@@ -2,6 +2,7 @@
 /* Copyright 2019 Linaro, Ltd, Rob Herring <robh@kernel.org> */
 /* Copyright 2023 Collabora ltd. */
 
+#include <linux/cleanup.h>
 #include <linux/dma-buf.h>
 #include <linux/dma-mapping.h>
 #include <linux/err.h>
@@ -18,6 +19,14 @@ static void panthor_gem_free_object(struct drm_gem_object *obj)
 	struct panthor_gem_object *bo = to_panthor_bo(obj);
 	struct drm_gem_object *vm_root_gem = bo->exclusive_vm_root_gem;
 
+	/*
+	 * Label might have been allocated with kstrdup_const(),
+	 * we need to take that into account when freeing the memory
+	 */
+	kfree_const(bo->label.str);
+
+	mutex_destroy(&bo->label.lock);
+
 	drm_gem_free_mmap_offset(&bo->base.base);
 	mutex_destroy(&bo->gpuva_list_lock);
 	drm_gem_shmem_free(&bo->base);
@@ -185,6 +194,7 @@ struct drm_gem_object *panthor_gem_create_object(struct drm_device *ddev, size_t
 	obj->base.map_wc = !ptdev->coherent;
 	mutex_init(&obj->gpuva_list_lock);
 	drm_gem_gpuva_set_lock(&obj->base.base, &obj->gpuva_list_lock);
+	mutex_init(&obj->label.lock);
 
 	return &obj->base.base;
 }
@@ -236,3 +246,39 @@ panthor_gem_create_with_handle(struct drm_file *file,
 
 	return ret;
 }
+
+void
+panthor_gem_bo_set_label(struct drm_gem_object *obj, const char *label)
+{
+	struct panthor_gem_object *bo = to_panthor_bo(obj);
+	const char *old_label;
+
+	scoped_guard(mutex, &bo->label.lock) {
+		old_label = bo->label.str;
+		bo->label.str = label;
+	}
+
+	kfree_const(old_label);
+}
+
+void
+panthor_gem_kernel_bo_set_label(struct panthor_kernel_bo *bo, const char *label)
+{
+	const char *str;
+
+	/* We should never attempt labelling a UM-exposed GEM object */
+	if (drm_WARN_ON(bo->obj->dev, bo->obj->handle_count > 0))
+		return;
+
+	if (!label)
+		return;
+
+	str = kstrdup_const(label, GFP_KERNEL);
+	if (!str) {
+		/* Failing to allocate memory for a label isn't a fatal condition */
+		drm_warn(bo->obj->dev, "Not enough memory to allocate BO label");
+		return;
+	}
+
+	panthor_gem_bo_set_label(bo->obj, str);
+}
diff --git a/drivers/gpu/drm/panthor/panthor_gem.h b/drivers/gpu/drm/panthor/panthor_gem.h
index 1a363bb814f4..af0d77338860 100644
--- a/drivers/gpu/drm/panthor/panthor_gem.h
+++ b/drivers/gpu/drm/panthor/panthor_gem.h
@@ -46,6 +46,20 @@ struct panthor_gem_object {
 
 	/** @flags: Combination of drm_panthor_bo_flags flags. */
 	u32 flags;
+
+	/**
+	 * @label: BO tagging fields. The label can be assigned within the
+	 * driver itself or through a specific IOCTL.
+	 */
+	struct {
+		/**
+		 * @label.str: Pointer to NULL-terminated string,
+		 */
+		const char *str;
+
+		/** @lock.str: Protects access to the @label.str field. */
+		struct mutex lock;
+	} label;
 };
 
 /**
@@ -91,6 +105,9 @@ panthor_gem_create_with_handle(struct drm_file *file,
 			       struct panthor_vm *exclusive_vm,
 			       u64 *size, u32 flags, uint32_t *handle);
 
+void panthor_gem_bo_set_label(struct drm_gem_object *obj, const char *label);
+void panthor_gem_kernel_bo_set_label(struct panthor_kernel_bo *bo, const char *label);
+
 static inline u64
 panthor_kernel_bo_gpuva(struct panthor_kernel_bo *bo)
 {