Re: [PATCH v20 18/22] cxl: Allow region creation by type2 drivers

Jonathan Cameron
2025-11-12T16:19:46Z

On Mon, 10 Nov 2025 15:36:53 +0000
alejandro.lucero-palau@amd.com wrote:

> From: Alejandro Lucero <alucerop@amd.com>
>
> Creating a CXL region requires userspace intervention through the cxl
> sysfs files. Type2 support should allow accelerator drivers to create
> such cxl region from kernel code.
>
> Adding that functionality and integrating it with current support for
> memory expanders. Only support uncommitted CXL_DECODER_DEVMEM decoders.
>
> Based on https://lore.kernel.org/linux-cxl/168592159835.1948938.1647215579839222774.stgit@dwillia2-xfh.jf.intel.com/
>
> Signed-off-by: Alejandro Lucero <alucerop@amd.com>
One minor suggestion that I made very late in v19 thread.
Either way:
Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>

> diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
> index 2424d1b35cee..63c9c5f92252 100644
> --- a/drivers/cxl/core/region.c
> +++ b/drivers/cxl/core/region.c

...

> +static struct cxl_region *
> +__construct_new_region(struct cxl_root_decoder *cxlrd,
> + struct cxl_endpoint_decoder **cxled, int ways)
> +{
> + struct cxl_memdev *cxlmd = cxled_to_memdev(cxled[0]);
> + struct cxl_decoder *cxld = &cxlrd->cxlsd.cxld;
> + struct cxl_region_params *p;
> + resource_size_t size = 0;
> + int rc, i;
> +
> + struct cxl_region *cxlr __free(cxl_region_drop) =
> + construct_region_begin(cxlrd, cxled[0]);
> + if (IS_ERR(cxlr))
> + return cxlr;
> +
> + guard(rwsem_write)(&cxl_rwsem.region);
> +
> + /*
> + * Sanity check. This should not happen with an accel driver handling
> + * the region creation.
> + */
> + p = &cxlr->params;
> + if (p->state >= CXL_CONFIG_INTERLEAVE_ACTIVE) {
> + dev_err(cxlmd->dev.parent,
> + "%s:%s: %s unexpected region state\n",
> + dev_name(&cxlmd->dev), dev_name(&cxled[0]->cxld.dev),
> + __func__);
> + return ERR_PTR(-EBUSY);
> + }
> +
> + rc = set_interleave_ways(cxlr, ways);
> + if (rc)
> + return ERR_PTR(rc);
> +
> + rc = set_interleave_granularity(cxlr, cxld->interleave_granularity);
> + if (rc)
> + return ERR_PTR(rc);
> +
> + scoped_guard(rwsem_read, &cxl_rwsem.dpa) {
> + for (i = 0; i < ways; i++) {
> + if (!cxled[i]->dpa_res)
> + break;
> + size += resource_size(cxled[i]->dpa_res);
> + }
> + if (i < ways)
> + return ERR_PTR(-EINVAL);

I came in late on v19 thread with a comment on this.

for (i = 0; i < ways; i++) {
if (!cxled[i]->dpa_res)
return ERR_PTR(-EINVAL);
size += resource_size(cxled[i]->dpa_res);
}
Is the same but simpler.

> +
> + rc = alloc_hpa(cxlr, size);
> + if (rc)
> + return ERR_PTR(rc);
> +
> + for (i = 0; i < ways; i++) {
> + rc = cxl_region_attach(cxlr, cxled[i], 0);
> + if (rc)
> + return ERR_PTR(rc);
> + }
> + }
> +
> + rc = cxl_region_decode_commit(cxlr);
> + if (rc)
> + return ERR_PTR(rc);
> +
> + p->state = CXL_CONFIG_COMMIT;
> +
> + return no_free_ptr(cxlr);
> +}