Re: [PATCH v3 2/6] drm/mm: Introduce address space shifting

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

On Tue, Aug 19, 2025 at 12:11:20PM +0200, Maarten Lankhorst wrote:
> From: Tomasz Lis <tomasz.lis@intel.com>
> 
> Due to resource reprovisioning, sometimes a need arises to move
> a living address space to a new area, preserving all the nodes
> and holes stored within.
> 
> It is possible to do that by removing all nodes to a temporary list,
> reiniting the drm_mm instance and re-adding everything while applying
> a shift to each node. But that is a lot of extra work for a task
> which could be done internally without any node shuffle operations.
> 
> This change introduces an interface which allows to shift the range
> without pruning the whole drm_mm instance.
> 
> Having a drm_mm interface for such shift significantly simplifies
> the code required to adjust a KMD for a change in base address
> of a space managed by drm_mm instance.
> 
> Signed-off-by: Tomasz Lis <tomasz.lis@intel.com>
> Link: https://lore.kernel.org/r/20250204224136.3183710-2-tomasz.lis@intel.com
> Signed-off-by: Maarten Lankhorst <dev@lankhorst.se>

Reviewed-by: Matthew Brost <matthew.brost@intel.com>

> ---
>  drivers/gpu/drm/drm_mm.c | 24 ++++++++++++++++++++++++
>  include/drm/drm_mm.h     |  1 +
>  2 files changed, 25 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_mm.c b/drivers/gpu/drm/drm_mm.c
> index ca254611b3823..ce3bd8b5e41f0 100644
> --- a/drivers/gpu/drm/drm_mm.c
> +++ b/drivers/gpu/drm/drm_mm.c
> @@ -917,6 +917,30 @@ struct drm_mm_node *drm_mm_scan_color_evict(struct drm_mm_scan *scan)
>  }
>  EXPORT_SYMBOL(drm_mm_scan_color_evict);
>  
> +/**
> + * drm_mm_shift - move the range of addresses managed by this @mm
> + * @mm: the drm_mm structure instance to shift
> + * @shift: the shift value to be added to addresses of all nodes
> + *
> + * The function shifts all nodes by given offset, moving the address space
> + * range managed by this @mm.
> + */
> +void drm_mm_shift(struct drm_mm *mm, s64 shift)
> +{
> +	struct drm_mm_node *node;
> +
> +	/*
> +	 * Head node represents a hole, with negative size and start at the end
> +	 * of addressable area. This means it is never present within nodes
> +	 * list - needs to be shifted separately.
> +	 */
> +	mm->head_node.start += shift;
> +
> +	drm_mm_for_each_node(node, mm)
> +		node->start += shift;
> +}
> +EXPORT_SYMBOL(drm_mm_shift);
> +
>  /**
>   * drm_mm_init - initialize a drm-mm allocator
>   * @mm: the drm_mm structure to initialize
> diff --git a/include/drm/drm_mm.h b/include/drm/drm_mm.h
> index f654874c4ce67..798e5a4f07add 100644
> --- a/include/drm/drm_mm.h
> +++ b/include/drm/drm_mm.h
> @@ -465,6 +465,7 @@ static inline int drm_mm_insert_node(struct drm_mm *mm,
>  void drm_mm_remove_node(struct drm_mm_node *node);
>  void drm_mm_init(struct drm_mm *mm, u64 start, u64 size);
>  void drm_mm_takedown(struct drm_mm *mm);
> +void drm_mm_shift(struct drm_mm *mm, s64 shift);
>  
>  /**
>   * drm_mm_clean - checks whether an allocator is clean
> -- 
> 2.50.0
>