Re: [PATCH v7 08/12] drm/xe: Make xe_ggtt_node offset relative to starting offset

[Matthew Brost <matthew.brost@intel.com>]

On Wed, Oct 15, 2025 at 09:47:17AM +0200, Maarten Lankhorst wrote:
> This will make node shifting in the next commit a one-liner.
> 
> Signed-off-by: Maarten Lankhorst <dev@lankhorst.se>
> ---
>  drivers/gpu/drm/xe/xe_ggtt.c | 21 ++++++++++++++-------
>  1 file changed, 14 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/gpu/drm/xe/xe_ggtt.c b/drivers/gpu/drm/xe/xe_ggtt.c
> index 5c07d63189ab1..1c97a06424b5c 100644
> --- a/drivers/gpu/drm/xe/xe_ggtt.c
> +++ b/drivers/gpu/drm/xe/xe_ggtt.c
> @@ -289,7 +289,7 @@ static void __xe_ggtt_init_early(struct xe_ggtt *ggtt, u64 start, u64 size)
>  {
>  	ggtt->start = start;
>  	ggtt->size = size;
> -	drm_mm_init(&ggtt->mm, start, size);
> +	drm_mm_init(&ggtt->mm, 0, size - start);

We should probably fix the drm_mm_init function signature so the last
argument is called 'end' rather than 'size'. Can be done in a follow up
though.

>  }
>  
>  int xe_ggtt_init_kunit(struct xe_ggtt *ggtt, u32 start, u32 size)
> @@ -388,7 +388,7 @@ static void xe_ggtt_initial_clear(struct xe_ggtt *ggtt)
>  	/* Display may have allocated inside ggtt, so be careful with clearing here */
>  	mutex_lock(&ggtt->lock);
>  	drm_mm_for_each_hole(hole, &ggtt->mm, start, end)
> -		xe_ggtt_clear(ggtt, start, end - start);
> +		xe_ggtt_clear(ggtt, ggtt->start + start, end - start);
>  
>  	xe_ggtt_invalidate(ggtt);
>  	mutex_unlock(&ggtt->lock);
> @@ -405,7 +405,7 @@ static void ggtt_node_remove(struct xe_ggtt_node *node)
>  
>  	mutex_lock(&ggtt->lock);
>  	if (bound)
> -		xe_ggtt_clear(ggtt, node->base.start, node->base.size);
> +		xe_ggtt_clear(ggtt, xe_ggtt_node_addr(node), node->base.size);
>  	drm_mm_remove_node(&node->base);
>  	node->base.size = 0;
>  	mutex_unlock(&ggtt->lock);
> @@ -561,13 +561,13 @@ int xe_ggtt_node_insert_balloon_locked(struct xe_ggtt_node *node, u64 start, u64
>  	lockdep_assert_held(&ggtt->lock);
>  
>  	node->base.color = 0;
> -	node->base.start = start;
> +	node->base.start = start - ggtt->start;
>  	node->base.size = end - start;
>  
>  	err = drm_mm_reserve_node(&ggtt->mm, &node->base);
>  
>  	if (xe_tile_WARN(ggtt->tile, err, "Failed to balloon GGTT %#llx-%#llx (%pe)\n",
> -			 node->base.start, node->base.start + node->base.size, ERR_PTR(err)))
> +			 xe_ggtt_node_addr(node), xe_ggtt_node_addr(node) + node->base.size, ERR_PTR(err)))
>  		return err;
>  
>  	xe_ggtt_dump_node(ggtt, &node->base, "balloon");
> @@ -744,7 +744,7 @@ static void xe_ggtt_map_bo(struct xe_ggtt *ggtt, struct xe_ggtt_node *node,
>  	if (XE_WARN_ON(!node))
>  		return;
>  
> -	start = node->base.start;
> +	start = xe_ggtt_node_addr(node);
>  	end = start + xe_bo_size(bo);
>  
>  	if (!xe_bo_is_vram(bo) && !xe_bo_is_stolen(bo)) {
> @@ -865,6 +865,13 @@ static int __xe_ggtt_insert_bo_at(struct xe_ggtt *ggtt, struct xe_bo *bo,
>  	}
>  
>  	mutex_lock(&ggtt->lock);
> +	if (start >= ggtt->start)
> +		start -= ggtt->start;
> +	else
> +		start = 0;

Does this logic work if let's say start == 0x1000 and ggtt->start ==
0x2000. It seems like that is caller bug which we should assert 'start
>= ggtt->start', right?

> +
> +	end -= ggtt->start;
> +
>  	err = drm_mm_insert_node_in_range(&ggtt->mm, &bo->ggtt_node[tile_id]->base,
>  					  xe_bo_size(bo), alignment, 0, start, end, 0);
>  	if (err) {
> @@ -1106,5 +1113,5 @@ u64 xe_ggtt_read_pte(struct xe_ggtt *ggtt, u64 offset)
>   */
>  u64 xe_ggtt_node_addr(const struct xe_ggtt_node *node)
>  {
> -	return node->base.start;
> +	return node->base.start + READ_ONCE(node->ggtt->start);

Why the READ_ONCE here?

Matt

>  }
> -- 
> 2.51.0
>