Re: [RFC v2 05/15] cxl: introduce cxl_get_committed_regions()

Jonathan Cameron
2025-12-22T12:31:54Z

On Tue, 9 Dec 2025 22:20:09 +0530
mhonap@nvidia.com wrote:

> From: Zhi Wang <zhiw@nvidia.com>
>
> The kernel CXL core can discover the configured and committed CXL regions
> from BIOS or firmware, respect its configuration and create the related
> kernel CXL core data structures without configuring and committing the CXL
> region.
>
> However, those information are kept within the kernel CXL core. A type-2
> device can have the same usage and a type-2 driver would like to know
> about it before creating the CXL regions.
>
> Introduce cxl_get_committed_regions() for a type-2 driver to discover the
> committed regions.
>
> Signed-off-by: Zhi Wang <zhiw@nvidia.com>
> Signed-off-by: Manish Honap <mhonap@nvidia.com>
A few trivial things inline.

Thanks,

Jonathan

> ---
> drivers/cxl/core/region.c | 73 +++++++++++++++++++++++++++++++++++++++
> include/cxl/cxl.h | 1 +
> 2 files changed, 74 insertions(+)
>
> diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
> index e89a98780e76..6c368b4641f1 100644
> --- a/drivers/cxl/core/region.c
> +++ b/drivers/cxl/core/region.c
> @@ -2785,6 +2785,79 @@ int cxl_get_region_range(struct cxl_region *region, struct range *range)
> }
> EXPORT_SYMBOL_NS_GPL(cxl_get_region_range, "CXL");
>
> +struct match_region_info {
> + struct cxl_memdev *cxlmd;
> + struct cxl_region **cxlrs;
> + int nr_regions;
> +};
> +
> +static int match_region_by_device(struct device *match, void *data)
> +{
> + struct match_region_info *info = data;
> + struct cxl_endpoint_decoder *cxled;
> + struct cxl_memdev *cxlmd;
> + struct cxl_region_params *p;
> + struct cxl_region *cxlr;
> + int i;
> +
> + if (!is_cxl_region(match))
> + return 0;
> +
> + lockdep_assert_held(&cxl_rwsem.region);
> + cxlr = to_cxl_region(match);
> + p = &cxlr->params;
> +
> + if (p->state != CXL_CONFIG_COMMIT)
> + return 0;
> +
> + for (i = 0; i < p->nr_targets; i++) {
> + void *cxlrs;

Might be worth giving this a type.

> +
> + cxled = p->targets[i];
> + cxlmd = cxled_to_memdev(cxled);
> +
> + if (info->cxlmd != cxlmd)
> + continue;
> +
> + cxlrs = krealloc(info->cxlrs, sizeof(cxlr) * (info->nr_regions + 1),
> + GFP_KERNEL);

krealloc_array() slightly better here I think.

> + if (!cxlrs) {
> + kfree(info->cxlrs);
> + return -ENOMEM;
> + }
> + info->cxlrs = cxlrs;
> +
> + info->cxlrs[info->nr_regions++] = cxlr;
> + }
> +
> + return 0;
> +}
> +
> +int cxl_get_committed_regions(struct cxl_memdev *cxlmd, struct cxl_region ***cxlrs, int *num)
> +{
> + struct match_region_info info = {0};
> + int ret = 0;

Always set, so don't initialize here.

> +
> + ret = down_write_killable(&cxl_rwsem.region);

Look at the ACQUIRE() stuff for this.

> + if (ret)
> + return ret;
> +
> + info.cxlmd = cxlmd;
> +
> + ret = bus_for_each_dev(&cxl_bus_type, NULL, &info, match_region_by_device);
> + if (ret) {
> + kfree(info.cxlrs);

With acquire magic above, ran return directly here.

> + } else {
> + *cxlrs = info.cxlrs;
> + *num = info.nr_regions;
> + }
> +
> + up_write(&cxl_rwsem.region);
> +
> + return ret;
> +}
> +EXPORT_SYMBOL_NS_GPL(cxl_get_committed_regions, "CXL");
> +
> static ssize_t __create_region_show(struct cxl_root_decoder *cxlrd, char *buf)
> {
> return sysfs_emit(buf, "region%u\n", atomic_read(&cxlrd->region_id));
> diff --git a/include/cxl/cxl.h b/include/cxl/cxl.h
> index e3bf8cf0b6d6..0a1f245557f4 100644
> --- a/include/cxl/cxl.h
> +++ b/include/cxl/cxl.h
> @@ -295,5 +295,6 @@ int cxl_get_region_range(struct cxl_region *region, struct range *range);
> int cxl_get_hdm_reg_info(struct cxl_dev_state *cxlds, u64 *count, u64 *offset,
> u64 *size);
> int cxl_find_comp_regblock_offset(struct pci_dev *pdev, u64 *offset);
> +int cxl_get_committed_regions(struct cxl_memdev *cxlmd, struct cxl_region ***cxlrs, int *num);
>
> #endif /* __CXL_CXL_H__ */