Re: [PATCH 01/18] drm: Introduce drm_mm_create_block()

[Ben Widawsky <ben@bwidawsk.net>]

On Fri, 19 Oct 2012 18:03:07 +0100
Chris Wilson <chris@chris-wilson.co.uk> wrote:

> To be used later by i915 to preallocate exact blocks of space from the
> range manager.
> 
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Dave Airlie <airlied@redhat.com>
> Cc: dri-devel@lists.freedestkop.org

With bikesheds below addressed or not:
Reviewed-by: Ben Widawsky <ben@bwidawsk.net>
> ---
>  drivers/gpu/drm/drm_mm.c |   49
> ++++++++++++++++++++++++++++++++++++++++++++++
> include/drm/drm_mm.h     |    4 ++++ 2 files changed, 53 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_mm.c b/drivers/gpu/drm/drm_mm.c
> index 9bb82f7..5db8c20 100644
> --- a/drivers/gpu/drm/drm_mm.c
> +++ b/drivers/gpu/drm/drm_mm.c
> @@ -161,6 +161,55 @@ static void drm_mm_insert_helper(struct
> drm_mm_node *hole_node, }
>  }
>  
> +struct drm_mm_node *drm_mm_create_block(struct drm_mm *mm,
> +					unsigned long start,
> +					unsigned long size,
> +					bool atomic)
> +{

<bikeshed>
You could add a best_fit field like some of the other interfaces which
will try to find a start == hole_start and end == hole_end. I'd guess
this interface won't be called enough to worry about fragmentation too
much though.
</bikeshed>

> +	struct drm_mm_node *hole, *node;
> +	unsigned long end = start + size;
> +
> +	list_for_each_entry(hole, &mm->hole_stack, hole_stack) {
> +		unsigned long hole_start;
> +		unsigned long hole_end;
> +
> +		BUG_ON(!hole->hole_follows);

<bikeshed>
This isn't bad, but I don't think sticking the bug here is all that
helpful in finding where the bug occured, since it wasn't here. WARN is
perhaps more useful, but equally unhelpful IMO.
</bikeshed>

> +		hole_start = drm_mm_hole_node_start(hole);
> +		hole_end = drm_mm_hole_node_end(hole);
> +
> +		if (hole_start > start || hole_end < end)
> +			continue;
> +
> +		node = drm_mm_kmalloc(mm, atomic);
> +		if (unlikely(node == NULL))
> +			return NULL;
> +
> +		node->start = start;
> +		node->size = size;
> +		node->mm = mm;
> +		node->allocated = 1;
> +
> +		INIT_LIST_HEAD(&node->hole_stack);
> +		list_add(&node->node_list, &hole->node_list);
> +
> +		if (start == hole_start) {
> +			hole->hole_follows = 0;
> +			list_del_init(&hole->hole_stack);
> +		}
> +
> +		node->hole_follows = 0;
> +		if (end != hole_end) {
> +			list_add(&node->hole_stack, &mm->hole_stack);
> +			node->hole_follows = 1;
> +		}
> +
> +		return node;
> +	}
> +
> +	return NULL;
> +}
> +EXPORT_SYMBOL(drm_mm_create_block);
> +
>  struct drm_mm_node *drm_mm_get_block_generic(struct drm_mm_node
> *hole_node, unsigned long size,
>  					     unsigned alignment,
> diff --git a/include/drm/drm_mm.h b/include/drm/drm_mm.h
> index 06d7f79..4020f96 100644
> --- a/include/drm/drm_mm.h
> +++ b/include/drm/drm_mm.h
> @@ -102,6 +102,10 @@ static inline bool drm_mm_initialized(struct
> drm_mm *mm) /*
>   * Basic range manager support (drm_mm.c)
>   */
> +extern struct drm_mm_node *drm_mm_create_block(struct drm_mm *mm,
> +					       unsigned long start,
> +					       unsigned long size,
> +					       bool atomic);
>  extern struct drm_mm_node *drm_mm_get_block_generic(struct
> drm_mm_node *node, unsigned long size,
>  						    unsigned
> alignment,



-- 
Ben Widawsky, Intel Open Source Technology Center