Re: [PATCH v10 06/24] firmware: arm_scmi: Add basic Telemetry support

[Jonathan Cameron]

On Sun, 16 Aug 2026 00:25:46 +0100
Cristian Marussi <cristian.marussi@xxxxxxx> wrote:

> Add SCMIv4.0 Telemetry basic support to enable initialization and resources
> enumeration: add all the telemetry messages definitions and parsing logic
> but only a few simple state gathering protocol operations.
> 
> Signed-off-by: Cristian Marussi <cristian.marussi@xxxxxxx>
Obviously this is huge. I'm not going to look through it all today, but
some quick comments form the part I did look at.

Jonathan

...

> +static void scmi_telemetry_resources_free(void *arg)
> +{
> +	struct telemetry_info *ti = arg;
> +	struct scmi_telemetry_res_info *rinfo = ti->rinfo;
> +
> +	/* Ensure rinfo is no more accessible upfront */
> +	smp_store_release(&ti->rinfo, NULL);
> +
> +	for (int i = 0; i < rinfo->num_des; i++) {
> +		struct telemetry_de *tde = to_tde(rinfo->des[i]);
> +
> +		scmi_telemetry_free_tde_put(ti, tde);

		scmi_telemetry_free_tde_put(ti, to_tde(rinfo->des[i]));
Seems resonable to me and avoids the need for the local variable.

> +	}
> +	xa_destroy(&ti->xa_des);
> +	kfree(ti->tdes);
> +	kfree(rinfo->des);
> +	kfree(rinfo->dei_store);
> +	scmi_telemetry_groups_free(rinfo);
> +	kfree(rinfo->grps);
> +	kfree(rinfo->grps_store);
> +
> +	kfree(rinfo);
> +}

> +
> +/**
> + * scmi_telemetry_resources_enumerate  - Enumeration helper
> + * @ti: A reference to the telemetry info descriptor for this instance
> + *
> + * This helper is configured to be called once on the first enumeration
> + * attempt, when triggered by invoking ti->res_get() from somewhere else.
> + * Once run it substitues itself in ti->res_get() with the simple accessor
> + * __scmi_telemetry_resources_get, which returns a descriptor to the resources
> + * that were possibly discovered.
> + *
> + * Note that, while it attempts to fully enumerate Data Events and Groups, it
> + * does NOT fail when such enumerations fail, instead it simply gives up with
> + * the end result that only a partially populated, but consistent, resources
> + * descriptor will be returned; in such a case the incomplete descriptor will
> + * be marked as NOT fully_enumerated: this design enables the kernel to deal
> + * with badly implemented out-of-spec firmware support while keep on providing
> + * a minimal sane, albeit possibly incomplete, set of telemetry respources.
> + *
> + * Return: A reference to a fully or partially populated resources descriptor
> + */
> +static struct scmi_telemetry_res_info *
> +scmi_telemetry_resources_enumerate(struct telemetry_info *ti)
> +{
> +	struct scmi_telemetry_res_info *rinfo;
> +	struct device *dev = ti->ph->dev;
> +	int ret;
> +
> +	/* Ensure local rinfo is initialized */
> +	rinfo = smp_load_acquire(&ti->rinfo);
> +
> +	/*
> +	 * Ensure this init function can be called only once and
> +	 * handles properly concurrent calls.
> +	 */
> +	if (atomic_cmpxchg(&ti->rinfo_initializing, 0, 1)) {
> +		if (!completion_done(&ti->rinfo_initdone))

What's the logic here?  This waits only if others are already
waiting. Why?

> +			wait_for_completion(&ti->rinfo_initdone);
> +		goto out;

return 0;

> +	}
> +
> +	ret = scmi_telemetry_de_descriptors_get(ti);
> +	if (ret) {
> +		dev_err(dev, FW_BUG "Cannot fully enumerate DEs resources. Degraded system.\n");
> +		goto done;
> +	}
> +
> +	ret = scmi_telemetry_enumerate_groups_intervals(ti);
> +	if (ret) {
> +		dev_err(dev, FW_BUG "Cannot fully enumerate group intervals. Degraded system.\n");
> +		goto done;
> +	}
> +
> +	/* Enumeration was fully successful, ensure this is visbile */
> +	smp_store_release(&rinfo->fully_enumerated, true);
> +done:
> +	/* Disable initialization permanently */
> +	smp_store_mb(ti->res_get, __scmi_telemetry_resources_get);
> +	complete_all(&ti->rinfo_initdone);
> +
> +out:

labels that just result in returns rarely add to readability of code.
I'd just return early instead.

> +	return rinfo;
> +}
> +
> +/**
> + * scmi_telemetry_instance_init  - Instance initializer
> + * @ti: A reference to the telemetry info descriptor for this instance
> + *
> + * Note that this allocates and initialize all the resources possibly needed
> + * and then setups the @scmi_telemetry_resources_enumerate helper as the

sets up

> + * default method for the first call to ti->res_get(): this mechanism enables
> + * the possibility of optionally implementing deferred enumeration policies
> + * which optionally delay the discovery phase and related SCMI message exchanges
> + * to a later point in time.
> + *
> + * Return: 0 on Success, errno otherwise
> + */
> +static int scmi_telemetry_instance_init(struct telemetry_info *ti)
> +{
...

> diff --git a/include/linux/scmi_protocol.h b/include/linux/scmi_protocol.h
> index 5ab73b1ab9aa..2850b018da0d 100644
> --- a/include/linux/scmi_protocol.h
> +++ b/include/linux/scmi_protocol.h
> @@ -2,16 +2,18 @@
>  /*
>   * SCMI Message Protocol driver header
>   *
> - * Copyright (C) 2018-2021 ARM Ltd.
> + * Copyright (C) 2018-2026 ARM Ltd.
>   */
>  
>  #ifndef _LINUX_SCMI_PROTOCOL_H
>  #define _LINUX_SCMI_PROTOCOL_H
>  
>  #include <linux/bitfield.h>
> +#include <linux/bitops.h>
>  #include <linux/device.h>
>  #include <linux/notifier.h>
>  #include <linux/types.h>
> +#include <linux/uuid.h>
>  
>  #define SCMI_MAX_STR_SIZE		64
>  #define SCMI_SHORT_NAME_MAX_SIZE	16
> @@ -824,6 +826,184 @@ struct scmi_pinctrl_proto_ops {
>  	int (*pin_free)(const struct scmi_protocol_handle *ph, u32 pin);
>  };
>  
> +enum scmi_telemetry_de_type {

There is quite a bit of stuff here. Seems only related to telemetry
so maybe a more specific header makes sense for just scmi_telemetry?

The same applies for some of the other stuff already in this header
like the sensors protocol elements.

> +	SCMI_TLM_DE_TYPE_USPECIFIED,
> +	SCMI_TLM_DE_TYPE_ACCUMUL_IDLE_RESIDENCY,
> +	SCMI_TLM_DE_TYPE_ACCUMUL_IDLE_COUNTS,
> +	SCMI_TLM_DE_TYPE_ACCUMUL_OTHERS,
> +	SCMI_TLM_DE_TYPE_INSTA_IDLE_STATE,
> +	SCMI_TLM_DE_TYPE_INSTA_OTHERS,
> +	SCMI_TLM_DE_TYPE_AVERAGE,
> +	SCMI_TLM_DE_TYPE_STATUS,
> +	SCMI_TLM_DE_TYPE_RESERVED_START,
> +	SCMI_TLM_DE_TYPE_RESERVED_END = 0xef,
> +	SCMI_TLM_DE_TYPE_OEM_START = 0xf0,
> +	SCMI_TLM_DE_TYPE_OEM_END = 0xff,
> +};
> +
> +enum scmi_telemetry_compo_type {
> +	SCMI_TLM_COMPO_TYPE_USPECIFIED,
> +	SCMI_TLM_COMPO_TYPE_CPU,
> +	SCMI_TLM_COMPO_TYPE_CLUSTER,
> +	SCMI_TLM_COMPO_TYPE_GPU,
> +	SCMI_TLM_COMPO_TYPE_NPU,
> +	SCMI_TLM_COMPO_TYPE_INTERCONNECT,
> +	SCMI_TLM_COMPO_TYPE_MEM_CNTRL,
> +	SCMI_TLM_COMPO_TYPE_L1_CACHE,
> +	SCMI_TLM_COMPO_TYPE_L2_CACHE,
> +	SCMI_TLM_COMPO_TYPE_L3_CACHE,
> +	SCMI_TLM_COMPO_TYPE_LL_CACHE,
> +	SCMI_TLM_COMPO_TYPE_SYS_CACHE,
> +	SCMI_TLM_COMPO_TYPE_DISP_CNTRL,
> +	SCMI_TLM_COMPO_TYPE_IPU,
> +	SCMI_TLM_COMPO_TYPE_CHIPLET,
> +	SCMI_TLM_COMPO_TYPE_PACKAGE,
> +	SCMI_TLM_COMPO_TYPE_SOC,
> +	SCMI_TLM_COMPO_TYPE_SYSTEM,
> +	SCMI_TLM_COMPO_TYPE_SMCU,
> +	SCMI_TLM_COMPO_TYPE_ACCEL,
> +	SCMI_TLM_COMPO_TYPE_BATTERY,
> +	SCMI_TLM_COMPO_TYPE_CHARGER,
> +	SCMI_TLM_COMPO_TYPE_PMIC,
> +	SCMI_TLM_COMPO_TYPE_BOARD,
> +	SCMI_TLM_COMPO_TYPE_MEMORY,
> +	SCMI_TLM_COMPO_TYPE_PERIPH,
> +	SCMI_TLM_COMPO_TYPE_PERIPH_SUBC,
> +	SCMI_TLM_COMPO_TYPE_LID,
> +	SCMI_TLM_COMPO_TYPE_DISPLAY,
> +	SCMI_TLM_COMPO_TYPE_RESERVED_START = 0x1d,
> +	SCMI_TLM_COMPO_TYPE_RESERVED_END = 0xdf,
> +	SCMI_TLM_COMPO_TYPE_OEM_START = 0xe0,
> +	SCMI_TLM_COMPO_TYPE_OEM_END = 0xff,
> +};
> +
> +#define	SCMI_TLM_GET_UPDATE_INTERVAL_SECS(x)	(FIELD_GET(GENMASK(20, 5), (x)))
> +#define SCMI_TLM_GET_UPDATE_INTERVAL_EXP(x)	(sign_extend32((x), 4))
> +
> +#define SCMI_TLM_GET_UPDATE_INTERVAL(x)		(FIELD_GET(GENMASK(20, 0), (x)))
> +#define SCMI_TLM_BUILD_UPDATE_INTERVAL(s, e)				    \
> +	(FIELD_PREP(GENMASK(20, 5), (s)) | FIELD_PREP(GENMASK(4, 0), (e)))
> +
> +enum scmi_telemetry_collection {
> +	SCMI_TLM_ONDEMAND,
> +	SCMI_TLM_NOTIFICATION,
> +	SCMI_TLM_SINGLE_READ,
> +};
> +
> +#define SCMI_TLM_GRP_INVALID		0xFFFFFFFF
> +
> +struct scmi_telemetry_intervals {
> +	unsigned int grp_id;
> +	bool discrete;
> +	unsigned int num_intervals;
> +#define SCMI_TLM_UPDATE_INTVL_SEGMENT_LOW	0
> +#define SCMI_TLM_UPDATE_INTVL_SEGMENT_HIGH	1
> +#define SCMI_TLM_UPDATE_INTVL_SEGMENT_STEP	2
> +	unsigned int update_intervals[] __counted_by(num_intervals);
> +};
> +
> +struct scmi_telemetry_grp_info {
> +	unsigned int grp_id;
> +	unsigned int num_des;
> +	unsigned int num_intervals;
> +};
> +
> +struct scmi_telemetry_group {
> +	bool enabled;
> +	bool tstamp_enabled;
> +	unsigned int *des;
> +	char *des_str;
> +	struct scmi_telemetry_grp_info *info;
> +	unsigned int active_update_interval;
> +	struct scmi_telemetry_intervals *intervals;
> +	enum scmi_telemetry_collection current_mode;
> +};
> +
> +struct scmi_telemetry_de_info {
> +	unsigned int id;
> +	unsigned int grp_id;
> +	unsigned int data_sz;
> +	unsigned int type;
> +	unsigned int unit;
> +	int unit_exp;
> +	unsigned int ts_rate;
> +	unsigned int instance_id;
> +	unsigned int compo_instance_id;
> +	unsigned int compo_type;
> +	bool persistent;
> +	char name[16];
> +};
> +
> +struct scmi_telemetry_de {
> +	bool tstamp_support;
> +	bool fc_support;
> +	bool name_support;
> +	struct scmi_telemetry_de_info *info;
> +	struct scmi_telemetry_group *grp;
> +	bool enabled;
> +	bool tstamp_enabled;
> +};
> +
> +struct scmi_telemetry_res_info {
> +	bool fully_enumerated;
> +	unsigned int num_des;
> +	struct scmi_telemetry_de **des;
> +	struct scmi_telemetry_de_info *dei_store;
> +	unsigned int num_groups;
> +	struct scmi_telemetry_group *grps;
> +	struct scmi_telemetry_grp_info *grps_store;
> +};
> +
> +struct scmi_telemetry_base_info {
> +	unsigned int version;
> +	uuid_t primary_revision;
> +	unsigned int num_des;
> +	unsigned int num_groups;
> +	unsigned int num_intervals;
> +	unsigned int num_shmtis;
> +};
> +
> +struct scmi_telemetry_shmti_info {
> +	unsigned int sid;
> +	unsigned int len;
> +	unsigned long offset;
> +	phys_addr_t phys;
> +};
> +
> +struct scmi_telemetry_info {
> +	bool single_read_support;
> +	bool continuos_update_support;
> +	bool per_group_config_support;
> +	bool reset_support;
> +	bool fc_support;
> +	struct scmi_telemetry_base_info base;
> +	unsigned int active_update_interval;
> +	struct scmi_telemetry_intervals *intervals;
> +	struct scmi_telemetry_shmti_info **shmtis;
> +	unsigned int num_uuids;
> +	uuid_t **uuids;

I'm going to guess a __counted_by_ptr marking makes sense here.
(I haven't checked!) I won't bother calling out other cases, but
looks like there may well be some above.

> +	bool enabled;
> +	bool notif_enabled;
> +	enum scmi_telemetry_collection current_mode;
> +};