linux-kernel - Re: [RFC v2 05/15] cxl: introduce cxl_get_committed

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Message-ID: <20251222123149.00003f91@huawei.com>
Date: Mon, 22 Dec 2025 12:31:49 +0000
From: Jonathan Cameron <jonathan.cameron@...wei.com>
To: <mhonap@...dia.com>
CC: <aniketa@...dia.com>, <ankita@...dia.com>, <alwilliamson@...dia.com>,
	<vsethi@...dia.com>, <jgg@...dia.com>, <mochs@...dia.com>,
	<skolothumtho@...dia.com>, <alejandro.lucero-palau@....com>,
	<dave@...olabs.net>, <dave.jiang@...el.com>, <alison.schofield@...el.com>,
	<vishal.l.verma@...el.com>, <ira.weiny@...el.com>,
	<dan.j.williams@...el.com>, <jgg@...pe.ca>, <yishaih@...dia.com>,
	<kevin.tian@...el.com>, <cjia@...dia.com>, <kwankhede@...dia.com>,
	<targupta@...dia.com>, <zhiw@...dia.com>, <kjaju@...dia.com>,
	<linux-kernel@...r.kernel.org>, <linux-cxl@...r.kernel.org>,
	<kvm@...r.kernel.org>
Subject: Re: [RFC v2 05/15] cxl: introduce cxl_get_committed_regions()

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

> From: Zhi Wang <zhiw@...dia.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@...dia.com>
> Signed-off-by: Manish Honap <mhonap@...dia.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__ */