Re: [RFC 1/4] drm/pagemap: Add helper to access backing devmem allocation

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

On Wed, Sep 16, 2026 at 04:58:30PM +0530, Himal Prasad Ghimiray wrote:
> drm_pagemap_zdd is private, so add drm_pagemap_page_to_devmem() to let
> callers get the drm_pagemap_devmem backing a device-private/coherent
> page. Add a NULL stub for !CONFIG_ZONE_DEVICE.
> 
> Cc: Matthew Brost <matthew.brost@intel.com>

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

> Signed-off-by: Himal Prasad Ghimiray <himal.prasad.ghimiray@intel.com>
> ---
>  drivers/gpu/drm/drm_pagemap.c | 15 +++++++++++++++
>  include/drm/drm_pagemap.h     |  7 +++++++
>  2 files changed, 22 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_pagemap.c b/drivers/gpu/drm/drm_pagemap.c
> index 892b325fa99b..fc1a2825c807 100644
> --- a/drivers/gpu/drm/drm_pagemap.c
> +++ b/drivers/gpu/drm/drm_pagemap.c
> @@ -1432,6 +1432,21 @@ struct drm_pagemap *drm_pagemap_page_to_dpagemap(struct page *page)
>  }
>  EXPORT_SYMBOL_GPL(drm_pagemap_page_to_dpagemap);
>  
> +/**
> + * drm_pagemap_page_to_devmem() - Return the devmem allocation backing a page
> + * @page: The struct page.
> + *
> + * Return: The &drm_pagemap_devmem backing @page. Undefined if @page was not
> + * populated from a &drm_pagemap.
> + */
> +struct drm_pagemap_devmem *drm_pagemap_page_to_devmem(struct page *page)
> +{
> +	struct drm_pagemap_zdd *zdd = drm_pagemap_page_zone_device_data(page);
> +
> +	return zdd->devmem_allocation;
> +}
> +EXPORT_SYMBOL_GPL(drm_pagemap_page_to_devmem);
> +
>  /**
>   * drm_pagemap_populate_mm() - Populate a virtual range with device memory pages
>   * @dpagemap: Pointer to the drm_pagemap managing the device memory
> diff --git a/include/drm/drm_pagemap.h b/include/drm/drm_pagemap.h
> index 95eb4b66b057..376d7d400c8e 100644
> --- a/include/drm/drm_pagemap.h
> +++ b/include/drm/drm_pagemap.h
> @@ -257,6 +257,8 @@ struct drm_pagemap *drm_pagemap_create(struct drm_device *drm,
>  
>  struct drm_pagemap *drm_pagemap_page_to_dpagemap(struct page *page);
>  
> +struct drm_pagemap_devmem *drm_pagemap_page_to_devmem(struct page *page);
> +
>  void drm_pagemap_put(struct drm_pagemap *dpagemap);
>  
>  #else
> @@ -266,6 +268,11 @@ static inline struct drm_pagemap *drm_pagemap_page_to_dpagemap(struct page *page
>  	return NULL;
>  }
>  
> +static inline struct drm_pagemap_devmem *drm_pagemap_page_to_devmem(struct page *page)
> +{
> +	return NULL;
> +}
> +
>  static inline void drm_pagemap_put(struct drm_pagemap *dpagemap)
>  {
>  }
> -- 
> 2.43.0
>