Re: [PATCH RFC v2 07/18] cxl/mem: Expose device dynamic capacity configuration

[Dave Jiang]

On 8/28/23 22:20, ira.weiny@xxxxxxxxx wrote:
> From: Navneet Singh <navneet.singh@xxxxxxxxx>
>
> To properly configure CXL regions on Dynamic Capacity Devices (DCD),
> user space will need to know the details of the DC Regions available on
> a device.
>
> Expose driver dynamic capacity configuration through sysfs
> attributes.
>
> Co-developed-by: Navneet Singh <navneet.singh@xxxxxxxxx>
> Signed-off-by: Navneet Singh <navneet.singh@xxxxxxxxx>
> Signed-off-by: Ira Weiny <ira.weiny@xxxxxxxxx>
>
> ---
> Changes for v2:
> [iweiny: Rebased on latest master/type2 work]
> [iweiny: add documentation for sysfs entries]
> [iweiny: s/dc_regions_count/region_count/]
> [iweiny: s/dcY_size/regionY_size/]
> [alison: change size format to %#llx]
> [iweiny: change count format to %d]
> [iweiny: Formatting updates]
> [iweiny: Fix crash when device is not a mem device: found with cxl-test]
> ---
>   Documentation/ABI/testing/sysfs-bus-cxl | 17 ++++++++
>   drivers/cxl/core/memdev.c               | 77 +++++++++++++++++++++++++++++++++
>   2 files changed, 94 insertions(+)
>
> diff --git a/Documentation/ABI/testing/sysfs-bus-cxl b/Documentation/ABI/testing/sysfs-bus-cxl
> index 2268ffcdb604..aa65dc5b4e13 100644
> --- a/Documentation/ABI/testing/sysfs-bus-cxl
> +++ b/Documentation/ABI/testing/sysfs-bus-cxl
> @@ -37,6 +37,23 @@ Description:
>   		identically named field in the Identify Memory Device Output
>   		Payload in the CXL-2.0 specification.
>   
> +What:		/sys/bus/cxl/devices/memX/dc/region_count
> +Date:		July, 2023
> +KernelVersion:	v6.6
> +Contact:	linux-cxl@xxxxxxxxxxxxxxx
> +Description:
> +		(RO) Number of Dynamic Capacity (DC) regions supported on the
> +		device.  May be 0 if the device does not support Dynamic
> +		Capacity.
> +
> +What:		/sys/bus/cxl/devices/memX/dc/regionY_size
> +Date:		July, 2023
> +KernelVersion:	v6.6
> +Contact:	linux-cxl@xxxxxxxxxxxxxxx
> +Description:
> +		(RO) Size of the Dynamic Capacity (DC) region Y.  Only
> +		available on devices which support DC and only for those
> +		region indexes supported by the device.
>   
>   What:		/sys/bus/cxl/devices/memX/serial
>   Date:		January, 2022
> diff --git a/drivers/cxl/core/memdev.c b/drivers/cxl/core/memdev.c
> index 492486707fd0..397262e0ebd2 100644
> --- a/drivers/cxl/core/memdev.c
> +++ b/drivers/cxl/core/memdev.c
> @@ -101,6 +101,20 @@ static ssize_t pmem_size_show(struct device *dev, struct device_attribute *attr,
>   static struct device_attribute dev_attr_pmem_size =
>   	__ATTR(size, 0444, pmem_size_show, NULL);
>   
> +static ssize_t region_count_show(struct device *dev, struct device_attribute *attr,
> +				 char *buf)
> +{
> +	struct cxl_memdev *cxlmd = to_cxl_memdev(dev);
> +	struct cxl_memdev_state *mds = to_cxl_memdev_state(cxlmd->cxlds);
> +	int len = 0;
> +
> +	len = sysfs_emit(buf, "%d\n", mds->nr_dc_region);
> +	return len;
> +}
> +
> +struct device_attribute dev_attr_region_count =
> +	__ATTR(region_count, 0444, region_count_show, NULL);
> +
>   static ssize_t serial_show(struct device *dev, struct device_attribute *attr,
>   			   char *buf)
>   {
> @@ -454,6 +468,62 @@ static struct attribute *cxl_memdev_security_attributes[] = {
>   	NULL,
>   };
>   
> +static ssize_t show_size_regionN(struct cxl_memdev *cxlmd, char *buf, int pos)
> +{
> +	struct cxl_memdev_state *mds = to_cxl_memdev_state(cxlmd->cxlds);
> +
> +	return sysfs_emit(buf, "%#llx\n", mds->dc_region[pos].decode_len);
> +}
> +
> +#define REGION_SIZE_ATTR_RO(n)						\
> +static ssize_t region##n##_size_show(struct device *dev,		\
> +				     struct device_attribute *attr,	\
> +				     char *buf)				\
> +{									\
> +	return show_size_regionN(to_cxl_memdev(dev), buf, (n));		\
> +}									\
> +static DEVICE_ATTR_RO(region##n##_size)
> +REGION_SIZE_ATTR_RO(0);
> +REGION_SIZE_ATTR_RO(1);
> +REGION_SIZE_ATTR_RO(2);
> +REGION_SIZE_ATTR_RO(3);
> +REGION_SIZE_ATTR_RO(4);
> +REGION_SIZE_ATTR_RO(5);
> +REGION_SIZE_ATTR_RO(6);
> +REGION_SIZE_ATTR_RO(7);
> +
> +static struct attribute *cxl_memdev_dc_attributes[] = {
> +	&dev_attr_region0_size.attr,
> +	&dev_attr_region1_size.attr,
> +	&dev_attr_region2_size.attr,
> +	&dev_attr_region3_size.attr,
> +	&dev_attr_region4_size.attr,
> +	&dev_attr_region5_size.attr,
> +	&dev_attr_region6_size.attr,
> +	&dev_attr_region7_size.attr,
> +	&dev_attr_region_count.attr,
> +	NULL,
> +};
> +
> +static umode_t cxl_dc_visible(struct kobject *kobj, struct attribute *a, int n)
> +{
> +	struct device *dev = kobj_to_dev(kobj);
> +	struct cxl_memdev *cxlmd = to_cxl_memdev(dev);
> +	struct cxl_memdev_state *mds = to_cxl_memdev_state(cxlmd->cxlds);
> +
> +	/* Not a memory device */
> +	if (!mds)
> +		return 0;
> +
> +	if (a == &dev_attr_region_count.attr)
> +		return a->mode;
> +
> +	if (n < mds->nr_dc_region)
> +		return a->mode;

I would add a comment on who you are checking against nr_dc_region to 
make it obvious.

DJ

> +
> +	return 0;
> +}
> +
>   static umode_t cxl_memdev_visible(struct kobject *kobj, struct attribute *a,
>   				  int n)
>   {
> @@ -482,11 +552,18 @@ static struct attribute_group cxl_memdev_security_attribute_group = {
>   	.attrs = cxl_memdev_security_attributes,
>   };
>   
> +static struct attribute_group cxl_memdev_dc_attribute_group = {
> +	.name = "dc",
> +	.attrs = cxl_memdev_dc_attributes,
> +	.is_visible = cxl_dc_visible,
> +};
> +
>   static const struct attribute_group *cxl_memdev_attribute_groups[] = {
>   	&cxl_memdev_attribute_group,
>   	&cxl_memdev_ram_attribute_group,
>   	&cxl_memdev_pmem_attribute_group,
>   	&cxl_memdev_security_attribute_group,
> +	&cxl_memdev_dc_attribute_group,
>   	NULL,
>   };
>