Re: [PATCH 5/6] cxl: add CXL_REGION_SYSRAM_DEFAULT_* build options

["Cheatham, Benjamin" <benjamin.cheatham@amd.com>]

On 1/12/2026 10:35 AM, Gregory Price wrote:
> DEFAULT_OFFLINE: Blocks will be offline after being created.
> DEFAULT_ONLINE:  Blocks will be onlined in ZONE_MOVABLE
> DEFAULT_ONLINE_NORMAL: Blocks will be onliend in ZONE_NORMAL.
> 
> This prevents users from having to use the MHP auto-online build config,
> which may cause misbehaviors with other devices hotplugging memory.

Isn't the MHP auto-online build config still used in some flows? A quick note on
when that option will still be used would be nice.
> 
> Signed-off-by: Gregory Price <gourry@gourry.net>
> ---
>  drivers/cxl/Kconfig                      | 40 ++++++++++
>  drivers/cxl/core/memctrl/sysram_region.c | 94 ++++++++++++++++++------
>  2 files changed, 110 insertions(+), 24 deletions(-)
> 
> diff --git a/drivers/cxl/Kconfig b/drivers/cxl/Kconfig
> index 5aed1524f8f1..3e087c9d5ea7 100644
> --- a/drivers/cxl/Kconfig
> +++ b/drivers/cxl/Kconfig
> @@ -243,6 +243,46 @@ config CXL_REGION_CTRL_AUTO_SYSRAM
>  
>  endchoice
>  
> +choice
> +	prompt "CXL SYSRAM Auto Online Mode"
> +	depends on CXL_REGION
> +	default CXL_REGION_SYSRAM_DEFAULT_OFFLINE
> +	help
> +	  Select whether CXL memory hotplugged as System RAM should be
> +	  automatically onlined and in which zone. This applies when the
> +	  region controller is set to SYSRAM (either explicitly or via
> +	  the auto control mode).
> +
> +config CXL_REGION_SYSRAM_DEFAULT_OFFLINE
> +	bool "Offline"
> +	help
> +	  Leave the memory offline after hotplug. The memory must be
> +	  manually onlined via sysfs or other mechanisms before it can
> +	  be used by the system.
> +
> +	  This is the default and most conservative option.
> +
> +config CXL_REGION_SYSRAM_DEFAULT_ONLINE
> +	bool "Online (Movable)"
> +	help
> +	  Automatically online the memory as ZONE_MOVABLE after hotplug.
> +	  ZONE_MOVABLE memory can be used for user pages and is eligible
> +	  for memory hotremove, but cannot be used for kernel allocations.
> +
> +	  Select this for memory that may need to be hotremoved later.
> +
> +config CXL_REGION_SYSRAM_DEFAULT_ONLINE_NORMAL
> +	bool "Online (Normal)"
> +	help
> +	  Automatically online the memory as ZONE_NORMAL after hotplug.
> +	  ZONE_NORMAL memory can be used for all allocations including
> +	  kernel allocations, but may not be hotremovable.
> +
> +	  Select this for maximum memory utilization when hotremove is
> +	  not required.
> +
> +endchoice
> +
>  config CXL_REGION_INVALIDATION_TEST
>  	bool "CXL: Region Cache Management Bypass (TEST)"
>  	depends on CXL_REGION
> diff --git a/drivers/cxl/core/memctrl/sysram_region.c b/drivers/cxl/core/memctrl/sysram_region.c
> index a7570c8a54e1..2e2d9b59a725 100644
> --- a/drivers/cxl/core/memctrl/sysram_region.c
> +++ b/drivers/cxl/core/memctrl/sysram_region.c
> @@ -129,12 +129,69 @@ static int offline_memory_block_cb(struct memory_block *mem, void *arg)
>  	return *rc;
>  }
>  
> +static int cxl_sysram_online_memory(struct range *range, int online_type)
> +{
> +	struct online_memory_cb_arg cb_arg = {
> +		.online_type = online_type,
> +		.rc = 0,
> +	};
> +	int rc;
> +
> +	rc = walk_memory_blocks(range->start, range_len(range),
> +				&cb_arg, online_memory_block_cb);
> +	if (!rc)
> +		rc = cb_arg.rc;
> +
> +	return rc;
> +}
> +
> +static int cxl_sysram_offline_memory(struct range *range)
> +{
> +	int offline_rc = 0;
> +	int rc;
> +
> +	rc = walk_memory_blocks(range->start, range_len(range),
> +				&offline_rc, offline_memory_block_cb);
> +	if (!rc)
> +		rc = offline_rc;
> +
> +	return rc;
> +}

I think these two helpers can get moved into patch 2/6 when the 'store' attribute was defined. I don't
see anything that requires they're in this patch and it would help reduce churn.

> +
> +static int cxl_sysram_auto_online(struct device *dev, struct range *range)
> +{
> +	int online_type;
> +	int rc;
> +
> +	if (IS_ENABLED(CONFIG_CXL_REGION_SYSRAM_DEFAULT_OFFLINE))
> +		return 0;
> +
> +	if (IS_ENABLED(CONFIG_CXL_REGION_SYSRAM_DEFAULT_ONLINE))
> +		online_type = MMOP_ONLINE_MOVABLE;
> +	else if (IS_ENABLED(CONFIG_CXL_REGION_SYSRAM_DEFAULT_ONLINE_NORMAL))
> +		online_type = MMOP_ONLINE_KERNEL;
> +	else
> +		online_type = MMOP_ONLINE_MOVABLE;
> +
> +	rc = lock_device_hotplug_sysfs();
> +	if (rc)
> +		return rc;
> +
> +	rc = cxl_sysram_online_memory(range, online_type);
> +
> +	unlock_device_hotplug();
> +
> +	if (rc)
> +		dev_warn(dev, "auto-online failed: %d\n", rc);
> +
> +	return rc;
> +}
> +
>  static ssize_t state_store(struct device *dev,
>  			   struct device_attribute *attr,
>  			   const char *buf, size_t len)
>  {
>  	struct cxl_region *cxlr = to_cxl_region(dev);
> -	struct online_memory_cb_arg cb_arg;
>  	struct range range;
>  	int rc;
>  
> @@ -149,30 +206,14 @@ static ssize_t state_store(struct device *dev,
>  	if (rc)
>  		return rc;
>  
> -	if (sysfs_streq(buf, "online")) {
> -		cb_arg.online_type = MMOP_ONLINE_MOVABLE;
> -		cb_arg.rc = 0;
> -		rc = walk_memory_blocks(range.start, range_len(&range),
> -					&cb_arg, online_memory_block_cb);
> -		if (!rc)
> -			rc = cb_arg.rc;
> -	} else if (sysfs_streq(buf, "online_normal")) {
> -		cb_arg.online_type = MMOP_ONLINE;
> -		cb_arg.rc = 0;
> -		rc = walk_memory_blocks(range.start, range_len(&range),
> -					&cb_arg, online_memory_block_cb);
> -		if (!rc)
> -			rc = cb_arg.rc;
> -	} else if (sysfs_streq(buf, "offline")) {
> -		int offline_rc = 0;
> -
> -		rc = walk_memory_blocks(range.start, range_len(&range),
> -					&offline_rc, offline_memory_block_cb);
> -		if (!rc)
> -			rc = offline_rc;
> -	} else {
> +	if (sysfs_streq(buf, "online"))
> +		rc = cxl_sysram_online_memory(&range, MMOP_ONLINE_MOVABLE);
> +	else if (sysfs_streq(buf, "online_normal"))
> +		rc = cxl_sysram_online_memory(&range, MMOP_ONLINE);
> +	else if (sysfs_streq(buf, "offline"))
> +		rc = cxl_sysram_offline_memory(&range);
> +	else
>  		rc = -EINVAL;
> -	}
>  
>  	unlock_device_hotplug();
>  
> @@ -332,6 +373,10 @@ int devm_cxl_add_sysram_region(struct cxl_region *cxlr)
>  	dev_dbg(dev, "%s: added %llu bytes as System RAM\n", dev_name(dev),
>  		(unsigned long long)total_len);
>  
> +	rc = cxl_sysram_auto_online(dev, &range);
> +	if (rc)
> +		goto err_auto_online;
> +
>  	dev_set_drvdata(dev, data);
>  	rc = devm_device_add_group(dev, &cxl_sysram_region_group);
>  	if (rc)
> @@ -341,6 +386,7 @@ int devm_cxl_add_sysram_region(struct cxl_region *cxlr)
>  
>  err_add_group:
>  	dev_set_drvdata(dev, NULL);
> +err_auto_online:
>  	/* if this fails, memory cannot be removed from the system until reboot */
>  	remove_memory(range.start, range_len(&range));
>  err_add_memory: