Re: [PATCH v5 02/27] cxl/regs: Let a BAR-owning driver own the component register block

[Jonathan Cameron <jic23@kernel.org>]

On Thu, 17 Sep 2026 00:05:15 +0530
<mhonap@nvidia.com> wrote:

> From: Manish Honap <mhonap@nvidia.com>
> 
> cxl_map_component_regs() claims each mapped sub-block with
> devm_request_mem_region(). A driver that already requested the whole
> component register BAR, such as vfio-cxl, would then collide with that
> claim and fail to map the HDM decoder and RAS blocks.
> 
> Add cxl_reg_map_add_owned_resource() so such a driver records the
> resource it already owns on the register map, and skip the sub-block
> request when the block falls within an owned resource.

This seems a slightly odd intermediate point.

The assumption is that if owned the whole bar is owned - hence only
handle one owned region (no check if there is already one set?)
yet the code will try to map it if we get a request for something
outside of the region mapped (which can't exist).

This all makes me a little nervous.

> 
> Assisted-by: LLM
> Signed-off-by: Manish Honap <mhonap@nvidia.com>
> ---
>  drivers/cxl/core/regs.c | 17 +++++++++++++++--
>  include/cxl/cxl.h       |  2 ++
>  include/cxl/pci.h       |  3 +++
>  3 files changed, 20 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/cxl/core/regs.c b/drivers/cxl/core/regs.c
> index d79550dbb484..58a7c5cafb45 100644
> --- a/drivers/cxl/core/regs.c
> +++ b/drivers/cxl/core/regs.c
> @@ -216,6 +216,13 @@ void __iomem *devm_cxl_iomap_block(struct device *dev, resource_size_t addr,
>  }
>  EXPORT_SYMBOL_NS_GPL(devm_cxl_iomap_block, "CXL");
>  
> +void cxl_reg_map_add_owned_resource(struct cxl_register_map *map,
> +				    struct resource *res)
> +{
> +	map->owned = res;

As above, I think this needs a sanity check that a future driver
author doesn't think they can just add lots of these.
Absolute minimum is add some Docs.

> +}
> +EXPORT_SYMBOL_NS_GPL(cxl_reg_map_add_owned_resource, "CXL");
> +
>  int cxl_map_component_regs(const struct cxl_register_map *map,
>  			   struct cxl_component_regs *regs,
>  			   unsigned long map_mask)
> @@ -234,6 +241,7 @@ int cxl_map_component_regs(const struct cxl_register_map *map,
>  		struct mapinfo *mi = &mapinfo[i];
>  		resource_size_t addr;
>  		resource_size_t length;
> +		struct resource res;
>  
>  		if (!mi->rmap->valid)
>  			continue;
> @@ -241,8 +249,13 @@ int cxl_map_component_regs(const struct cxl_register_map *map,
>  			continue;
>  		addr = map->resource + mi->rmap->offset;
>  		length = mi->rmap->size;
> -		*(mi->addr) = devm_cxl_iomap_block(host, addr, length);
> -		if (!*(mi->addr))
> +		res = DEFINE_RES_MEM(addr, length);
> +
> +		if (map->owned && resource_contains(map->owned, &res))

If assumption is whole bar or none, should we just fail if map->owned is true
but the resource contains fails? 

> +			*mi->addr = devm_cxl_ioremap_block(host, addr, length);
> +		else
> +			*mi->addr = devm_cxl_iomap_block(host, addr, length);
> +		if (!*mi->addr)
>  			return -ENOMEM;
>  	}
>