Re: [PATCH v14 11/22] cxl: define a driver interface for HPA free space enumeration

[Jonathan Cameron <Jonathan.Cameron@huawei.com>]

On Thu, 17 Apr 2025 22:29:14 +0100
<alejandro.lucero-palau@amd.com> wrote:

> From: Alejandro Lucero <alucerop@amd.com>
> 
> CXL region creation involves allocating capacity from device DPA
> (device-physical-address space) and assigning it to decode a given HPA
> (host-physical-address space). Before determining how much DPA to
> allocate the amount of available HPA must be determined. Also, not all
> HPA is created equal, some specifically targets RAM, some target PMEM,
> some is prepared for device-memory flows like HDM-D and HDM-DB, and some
> is host-only (HDM-H).
> 
> Wrap all of those concerns into an API that retrieves a root decoder
> (platform CXL window) that fits the specified constraints and the
> capacity available for a new region.
> 
> Add a complementary function for releasing the reference to such root
> decoder.
> 
> Based on https://lore.kernel.org/linux-cxl/168592159290.1948938.13522227102445462976.stgit@dwillia2-xfh.jf.intel.com/
> 
> Signed-off-by: Alejandro Lucero <alucerop@amd.com>
> Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

> +	/*
> +	 * None flags are declared as bitmaps but for the sake of better code
> +	 * used here as such, restricting the bitmap size to those bits used by
> +	 * any Type2 device driver requester.

I'd just drop the comment as it's more confusing than helpful.

If you really want something then perhaps.

	* Flags are single unsigned longs. As CXL_DECODER_F_MAX is less than
	* 32 bits the bitmap functions may be used.

> +	 */
> +	if (!bitmap_subset(&ctx->flags, &cxld->flags, CXL_DECODER_F_MAX)) {
> +		dev_dbg(dev, "flags not matching: %08lx vs %08lx\n",
> +			cxld->flags, ctx->flags);
> +		return 0;
> +	}