Re: [PATCH 9/9] iosys_map: embed the is_iomem bit into the pointer.

[Jani Nikula <jani.nikula@linux.intel.com>]

On Thu, 22 May 2025, Dave Airlie <airlied@gmail.com> wrote:
> From: Dave Airlie <airlied@redhat.com>
>
> This reduces this struct from 16 to 8 bytes, and it gets embedded
> into a lot of things.

It's an abomination.

And i915 has helpers for it. Because of course it does.

i915_utils.h contains ptr_mask_bits(), ptr_unmask_bits(),
ptr_pack_bits() and ptr_unpack_bits() to do this, uh, cleanly.

Should we try to promote the helpers somewhere in include/linux and use
them here?


BR,
Jani.


>
> Signed-off-by: Dave Airlie <airlied@redhat.com>
> ---
>  include/linux/iosys-map.h | 30 ++++++++----------------------
>  1 file changed, 8 insertions(+), 22 deletions(-)
>
> diff --git a/include/linux/iosys-map.h b/include/linux/iosys-map.h
> index a6c2cc9ca756..44479966ce24 100644
> --- a/include/linux/iosys-map.h
> +++ b/include/linux/iosys-map.h
> @@ -99,29 +99,27 @@
>   *	iosys_map_incr(&map, len); // go to first byte after the memcpy
>   */
>  
> +#define _IOSYS_MAP_IS_IOMEM 1
>  /**
>   * struct iosys_map - Pointer to IO/system memory
>   * @vaddr_iomem:	The buffer's address if in I/O memory
>   * @vaddr:		The buffer's address if in system memory
> - * @is_iomem:		True if the buffer is located in I/O memory, or false
> - *			otherwise.
>   */
>  struct iosys_map {
>  	union {
>  		void __iomem *_vaddr_iomem;
>  		void *_vaddr;
>  	};
> -	bool _is_iomem;
>  };
>  
>  static inline bool iosys_map_is_iomem(const struct iosys_map *map)
>  {
> -	return map->_is_iomem;
> +	return ((unsigned long)map->_vaddr) & _IOSYS_MAP_IS_IOMEM;
>  }
>  
>  static inline void __iomem *iosys_map_ioptr(const struct iosys_map *map)
>  {
> -	return map->_vaddr_iomem;
> +	return (void __iomem *)((unsigned long)map->_vaddr_iomem & ~_IOSYS_MAP_IS_IOMEM);
>  }
>  
>  static inline void *iosys_map_ptr(const struct iosys_map *map)
> @@ -136,7 +134,6 @@ static inline void *iosys_map_ptr(const struct iosys_map *map)
>  #define IOSYS_MAP_INIT_VADDR(vaddr_)	\
>  	{				\
>  		._vaddr = (vaddr_),	\
> -		._is_iomem = false,	\
>  	}
>  
>  /**
> @@ -145,8 +142,7 @@ static inline void *iosys_map_ptr(const struct iosys_map *map)
>   */
>  #define IOSYS_MAP_INIT_VADDR_IOMEM(vaddr_iomem_)	\
>  	{						\
> -		._vaddr_iomem = (vaddr_iomem_),		\
> -		._is_iomem = true,			\
> +		._vaddr_iomem = (void __iomem *)(((unsigned long)(vaddr_iomem_) | _IOSYS_MAP_IS_IOMEM)), \
>  	}
>  
>  /**
> @@ -198,7 +194,6 @@ static inline void *iosys_map_ptr(const struct iosys_map *map)
>  static inline void iosys_map_set_vaddr(struct iosys_map *map, void *vaddr)
>  {
>  	map->_vaddr = vaddr;
> -	map->_is_iomem = false;
>  }
>  
>  /**
> @@ -211,8 +206,7 @@ static inline void iosys_map_set_vaddr(struct iosys_map *map, void *vaddr)
>  static inline void iosys_map_set_vaddr_iomem(struct iosys_map *map,
>  					     void __iomem *vaddr_iomem)
>  {
> -	map->_vaddr_iomem = vaddr_iomem;
> -	map->_is_iomem = true;
> +	map->_vaddr_iomem = (void __iomem *)((unsigned long)vaddr_iomem | _IOSYS_MAP_IS_IOMEM);
>  }
>  
>  /**
> @@ -229,12 +223,9 @@ static inline void iosys_map_set_vaddr_iomem(struct iosys_map *map,
>  static inline bool iosys_map_is_equal(const struct iosys_map *lhs,
>  				      const struct iosys_map *rhs)
>  {
> -	if (lhs->_is_iomem != rhs->_is_iomem)
> +	if (lhs->_vaddr != rhs->_vaddr)
>  		return false;
> -	else if (lhs->_is_iomem)
> -		return lhs->_vaddr_iomem == rhs->_vaddr_iomem;
> -	else
> -		return lhs->_vaddr == rhs->_vaddr;
> +	return true;
>  }
>  
>  /**
> @@ -279,12 +270,7 @@ static inline bool iosys_map_is_set(const struct iosys_map *map)
>   */
>  static inline void iosys_map_clear(struct iosys_map *map)
>  {
> -	if (map->_is_iomem) {
> -		map->_vaddr_iomem = NULL;
> -		map->_is_iomem = false;
> -	} else {
> -		map->_vaddr = NULL;
> -	}
> +	map->_vaddr = NULL;
>  }
>  
>  /**

-- 
Jani Nikula, Intel