Re: [RFC PATCH v2 3/5] acpi/hmat: Add helper functions to provide extended linear cache translation

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

On Tue, 12 Nov 2024 15:12:35 -0700
Dave Jiang <dave.jiang@intel.com> wrote:

> Add helper functions to help do address translation for either the address
> of the extended linear cache or its alias address. The translation function
> attempt to detect an I/O hole in the proximity domain and adjusts the
> address if the hole impacts the aliasing of the address. The range of the
> I/O hole is retrieved by walking through the associated memory target
> resources.
> 
> Signed-off-by: Dave Jiang <dave.jiang@intel.com>
> ---
Trivial comment inline.  I'm far from expert on requirements here but it
seems to match your description.

Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

> v2:
> - Drop extra variable and use 'res' from the loop. (Jonathan)
> - Break up multiple if statements into single blocks and add comments. (Jonathan)
> ---
>  drivers/acpi/numa/hmat.c | 148 +++++++++++++++++++++++++++++++++++++++
>  include/linux/acpi.h     |  14 ++++
>  2 files changed, 162 insertions(+)
> 
> diff --git a/drivers/acpi/numa/hmat.c b/drivers/acpi/numa/hmat.c
> index 92b818b72ecc..6c686d3c7266 100644
> --- a/drivers/acpi/numa/hmat.c
> +++ b/drivers/acpi/numa/hmat.c
> @@ -152,6 +152,154 @@ int hmat_get_extended_linear_cache_size(struct resource *backing_res, int nid,
>  }
>  EXPORT_SYMBOL_NS_GPL(hmat_get_extended_linear_cache_size, CXL);
>  
> +static int alias_address_find_iohole(struct memory_target *target,
> +				     u64 address, u64 alias, struct range *hole)
> +{
> +	struct resource *res, *prev;
> +
> +	*hole = (struct range) {
> +		.start = 0,
> +		.end = -1,
> +	};
> +
> +	/* First find the resource that the address is in */
> +	prev = target->memregions.child;
> +	for (res = target->memregions.child; res; res = res->sibling) {
> +		if (alias >= res->start && alias <= res->end)
> +			break;
> +		prev = res;
> +	}
> +	if (!res)
> +		return -EINVAL;
> +
> +	/* No memory hole */
> +	if (res == prev)
> +		return 0;
> +
> +	/* If address is within the current resource, no need to deal with memory hole */

Rather long line that could be easily broken.

> +	if (address >= res->start)
> +		return 0;
> +
> +	*hole = (struct range) {
> +		.start = prev->end + 1,
> +		.end = res->start - 1,
> +	};
> +
> +	return 0;
> +}