Subject: Re: [PATCH v10 14/26] cxl: define a driver interface for HPA free space enumeration

From: Simon Horman <[email-masked]>
Date: Fri, 7 Feb 2025 12:55:43 +0000

On Wed, Feb 05, 2025 at 03:19:38PM +0000, [email-masked] wrote:
> From: Alejandro Lucero <[email-masked]>
> 
> 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/[email-masked]/
> 
> Signed-off-by: Alejandro Lucero <[email-masked]>
> Co-developed-by: Dan Williams <[email-masked]>
> Reviewed-by: Jonathan Cameron <[email-masked]>
> ---
>  drivers/cxl/core/region.c | 160 ++++++++++++++++++++++++++++++++++++++
>  drivers/cxl/cxl.h         |   3 +
>  include/cxl/cxl.h         |  10 +++
>  3 files changed, 173 insertions(+)
> 
> diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
> index 84ce625b8591..69ff00154298 100644
> --- a/drivers/cxl/core/region.c
> +++ b/drivers/cxl/core/region.c
> @@ -695,6 +695,166 @@ static int free_hpa(struct cxl_region *cxlr)
>  	return 0;
>  }
>  
> +struct cxlrd_max_context {
> +	struct device * const *host_bridges;
> +	int interleave_ways;
> +	unsigned long flags;
> +	resource_size_t max_hpa;
> +	struct cxl_root_decoder *cxlrd;
> +};
> +
> +static int find_max_hpa(struct device *dev, void *data)
> +{
> +	struct cxlrd_max_context *ctx = data;
> +	struct cxl_switch_decoder *cxlsd;
> +	struct cxl_root_decoder *cxlrd;
> +	struct resource *res, *prev;
> +	struct cxl_decoder *cxld;
> +	resource_size_t max;
> +	int found;
> +
> +	if (!is_root_decoder(dev))
> +		return 0;
> +
> +	cxlrd = to_cxl_root_decoder(dev);
> +	cxlsd = &cxlrd->cxlsd;
> +	cxld = &cxlsd->cxld;
> +	if ((cxld->flags & ctx->flags) != ctx->flags) {
> +		dev_dbg(dev, "flags not matching: %08lx vs %08lx\n",
> +			cxld->flags, ctx->flags);
> +		return 0;
> +	}
> +
> +	for (int i = 0; i < ctx->interleave_ways; i++)
> +		for (int j = 0; j < ctx->interleave_ways; j++)
> +			if (ctx->host_bridges[i] == cxlsd->target[j]->dport_dev) {
> +				found++;

Hi Alejandro,

found is incremented here, but does not appear to have been initialised.

Flagged by W=1 build with clang-19, and by Smatch.

> +				break;
> +			}

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