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

From: Jonathan Cameron <[email-masked]>
Date: Wed, 12 Nov 2025 16:19:42 +0000

On Mon, 10 Nov 2025 15:36:53 +0000
[email-masked] wrote:

> From: Alejandro Lucero <[email-masked]>
> 
> 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/[email-masked]/
> 
> Signed-off-by: Alejandro Lucero <[email-masked]>
One minor suggestion that I made very late in v19 thread.
Either way:
Reviewed-by: Jonathan Cameron <[email-masked]>

> 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);
> +}