Re: [PATCH v4 13/28] cxl/mem: Expose DCD partition capabilities in sysfs

[Jonathan Cameron]

On Mon, 07 Oct 2024 18:16:19 -0500
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 partitions available.
> 
> Expose dynamic capacity capabilities through sysfs.
> 
> Signed-off-by: Navneet Singh <navneet.singh@xxxxxxxxx>
> Co-developed-by: Ira Weiny <ira.weiny@xxxxxxxxx>
> Signed-off-by: Ira Weiny <ira.weiny@xxxxxxxxx>
Some trivial stuff inline that I'm not that bothered about either way.

Subject to answering Fan's query
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx>

> 
> ---
> Changes:
> [iweiny: Change .../memX/dc/* to .../memX/dcY/*]
> [iweiny: add read only and shareable attributes from DSMAS]
> [djiang: Split sysfs docs]
> [iweiny: Adjust sysfs doc dates]
> [iweiny: Add qos details]
> ---
>  Documentation/ABI/testing/sysfs-bus-cxl |  45 ++++++++++++
>  drivers/cxl/core/memdev.c               | 126 ++++++++++++++++++++++++++++++++
>  2 files changed, 171 insertions(+)
> 
> diff --git a/Documentation/ABI/testing/sysfs-bus-cxl b/Documentation/ABI/testing/sysfs-bus-cxl
> index 3f5627a1210a..b865eefdb74c 100644
> --- a/Documentation/ABI/testing/sysfs-bus-cxl
> +++ b/Documentation/ABI/testing/sysfs-bus-cxl
> @@ -54,6 +54,51 @@ Description:
>  		identically named field in the Identify Memory Device Output
>  		Payload in the CXL-2.0 specification.
>  
> +What:		/sys/bus/cxl/devices/memX/dcY/size
> +Date:		December, 2024
> +KernelVersion:	v6.13
> +Contact:	linux-cxl@xxxxxxxxxxxxxxx
> +Description:
> +		(RO) Dynamic Capacity (DC) region information.  Devices only
> +		export dcY if DCD partition Y is supported.
> +		dcY/size is the size of each of those partitions.
> +
> +What:		/sys/bus/cxl/devices/memX/dcY/read_only
> +Date:		December, 2024
> +KernelVersion:	v6.13
> +Contact:	linux-cxl@xxxxxxxxxxxxxxx
> +Description:
> +		(RO) Dynamic Capacity (DC) region information.  Devices only
> +		export dcY if DCD partition Y is supported.
> +		dcY/read_only indicates true if the region is exported
> +		read_only from the device.
> +
> +What:		/sys/bus/cxl/devices/memX/dcY/shareable
> +Date:		December, 2024
> +KernelVersion:	v6.13
> +Contact:	linux-cxl@xxxxxxxxxxxxxxx
> +Description:
> +		(RO) Dynamic Capacity (DC) region information.  Devices only
> +		export dcY if DCD partition Y is supported.
> +		dcY/shareable indicates true if the region is exported
> +		shareable from the device.
> +
> +What:		/sys/bus/cxl/devices/memX/dcY/qos_class
> +Date:		December, 2024
> +KernelVersion:	v6.13
> +Contact:	linux-cxl@xxxxxxxxxxxxxxx
> +Description:
> +		(RO) Dynamic Capacity (DC) region information.  Devices only
> +		export dcY if DCD partition Y is supported.  

You can document sysfs directories I think, e.g.
https://elixir.bootlin.com/linux/v6.12-rc2/source/Documentation/ABI/stable/sysfs-devices-node#L32
so maybe

What:			/sys/bus/cxl/device/memX/dcY
Date:		December, 2024
KernelVersion:	v6.13
Contact:	linux-cxl@xxxxxxxxxxxxxxx
Description: 
		Directory containing Dynamic Capacity (DC) region information.
                Devices only export dcY if DCD partition Y is supported.

What:		/sys/bus/cxl/devices/memX/dcY/qos_class
Date:		December, 2024
KernelVersion:	v6.13
Contact:	linux-cxl@xxxxxxxxxxxxxxx
Description:
		For CXL host...

To avoid the repetition of first bit of docs?

> +		platforms that support "QoS Telemmetry" this attribute conveys
> +		a comma delimited list of platform specific cookies that
> +		identifies a QoS performance class for the persistent partition
> +		of the CXL mem device. These class-ids can be compared against
> +		a similar "qos_class" published for a root decoder. While it is
> +		not required that the endpoints map their local memory-class to
> +		a matching platform class, mismatches are not recommended and
> +		there are platform specific performance related side-effects
> +		that may result. First class-id is displayed.
>  
>  What:		/sys/bus/cxl/devices/memX/pmem/qos_class
>  Date:		May, 2023


> +static ssize_t show_shareable_dcN(struct cxl_memdev *cxlmd, char *buf, int pos)
> +{
> +	struct cxl_memdev_state *mds = to_cxl_memdev_state(cxlmd->cxlds);
> +
> +	return sysfs_emit(buf, "%s\n",
> +			  str_false_true(mds->dc_region[pos].shareable));

Fan has already raised that these seem backwards.

> +}
> +
> +static ssize_t show_qos_class_dcN(struct cxl_memdev *cxlmd, char *buf, int pos)
> +{
> +	struct cxl_memdev_state *mds = to_cxl_memdev_state(cxlmd->cxlds);
> +
> +	return sysfs_emit(buf, "%d\n", mds->dc_perf[pos].qos_class);
> +}
> +
> +#define CXL_MEMDEV_DC_ATTR_GROUP(n)						\
> +static ssize_t dc##n##_size_show(struct device *dev,				\
> +				 struct device_attribute *attr,			\
> +				 char *buf)					\
> +{										\
> +	return show_size_dcN(to_cxl_memdev(dev), buf, (n));			\
> +}										\
> +struct device_attribute dc##n##_size = {					\
> +	.attr	= { .name = "size", .mode = 0444 },				\
> +	.show	= dc##n##_size_show,						\
> +};										\
> +static ssize_t dc##n##_read_only_show(struct device *dev,			\
> +				      struct device_attribute *attr,		\
> +				      char *buf)				\
> +{										\
> +	return show_read_only_dcN(to_cxl_memdev(dev), buf, (n));		\
> +}										\
> +struct device_attribute dc##n##_read_only = {					\
> +	.attr	= { .name = "read_only", .mode = 0444 },			\
> +	.show	= dc##n##_read_only_show,					\
> +};										\
> +static ssize_t dc##n##_shareable_show(struct device *dev,			\
> +				     struct device_attribute *attr,		\
> +				     char *buf)					\
> +{										\
> +	return show_shareable_dcN(to_cxl_memdev(dev), buf, (n));		\
> +}										\
> +struct device_attribute dc##n##_shareable = {					\
> +	.attr	= { .name = "shareable", .mode = 0444 },			\
> +	.show	= dc##n##_shareable_show,					\
> +};										\
> +static ssize_t dc##n##_qos_class_show(struct device *dev,			\
> +				      struct device_attribute *attr,		\
> +				      char *buf)				\
> +{										\
> +	return show_qos_class_dcN(to_cxl_memdev(dev), buf, (n));		\
> +}										\
> +struct device_attribute dc##n##_qos_class = {					\
> +	.attr	= { .name = "qos_class", .mode = 0444 },			\
> +	.show	= dc##n##_qos_class_show,					\
> +};										\
> +static struct attribute *cxl_memdev_dc##n##_attributes[] = {			\
> +	&dc##n##_size.attr,							\
> +	&dc##n##_read_only.attr,						\
> +	&dc##n##_shareable.attr,						\
> +	&dc##n##_qos_class.attr,						\
> +	NULL,									\

No comma needed on terminator.

> +};										\
> +static umode_t cxl_memdev_dc##n##_attr_visible(struct kobject *kobj,		\
> +					       struct attribute *a,		\
> +					       int pos)				\
> +{										\
> +	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)								\
	if (!to_cxl_memdev_state(cxlmd->cxlds))
		return 0;

I dislike long macros so if we can shave them down that is always good!

We do have precedence in hdm.c for just checking the type directly so maybe
	if (cxlmd->cxlds->type != CXL_DEVTYPE_CLASSMEM)

but the above is also fine as compiler should be able to figure out it
doesn't need to do the second half of the inline.


> +		return 0;							\
> +	return a->mode;								\
> +}										\
> +static umode_t cxl_memdev_dc##n##_group_visible(struct kobject *kobj)		\
> +{										\
> +	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 or partition not supported */			\
> +	if (!mds || n >= mds->nr_dc_region)					\
> +		return false;							\
> +	return true;								\

	/* Memory device and partition is supported */
	return mds && n < mds->nr_dc_region;

> +}										\
>