Message-ID: <20260119162932.00006e6c@huawei.com>
Date: Mon, 19 Jan 2026 16:29:32 +0000
From: Jonathan Cameron <jonathan.cameron@...wei.com>
To: Cristian Marussi <cristian.marussi@....com>
CC: <linux-kernel@...r.kernel.org>, <linux-arm-kernel@...ts.infradead.org>,
	<arm-scmi@...r.kernel.org>, <linux-fsdevel@...r.kernel.org>,
	<sudeep.holla@....com>, <james.quinlan@...adcom.com>, <f.fainelli@...il.com>,
	<vincent.guittot@...aro.org>, <etienne.carriere@...com>,
	<peng.fan@....nxp.com>, <michal.simek@....com>, <dan.carpenter@...aro.org>,
	<d-gole@...com>, <elif.topuz@....com>, <lukasz.luba@....com>,
	<philip.radford@....com>, <souvik.chakravarty@....com>
Subject: Re: [PATCH v2 05/17] firmware: arm_scmi: Add Telemetry protocol
 support

On Wed, 14 Jan 2026 11:46:09 +0000
Cristian Marussi <cristian.marussi@....com> wrote:

> Add basic support for SCMI V4.0 Telemetry protocol including SHMTI,
> FastChannels, Notifications and Single Sample Reads collection methods.
> 
> Signed-off-by: Cristian Marussi <cristian.marussi@....com>
> ---
> v1 --> v2
>  - Add proper ioread accessors for TDCF areas
>  - Rework resource allocation logic and lifecycle
>  - Introduce new resources accessors and res_get() operation to
>    implement lazy enumeration
>  - Support boot-on telemetry:
>    + Add DE_ENABLED_LIST cmd support
>    + Add CONFIG_GET cmd support
>    + Add TDCF_SCAN for best effort enumeration
>    + Harden driver against out-of-spec FW with out of spec cmds
>  - Use FCs list
>  - Rework de_info_lookup to a moer general de_lookup
>  - Fixed reset to use CONFIG_GET and DE_ENABLED_LIST to gather initial
>    state
>  - Using sign_extend32 helper
>  - Added counted_by marker where appropriate
> ---
>  drivers/firmware/arm_scmi/Makefile    |    2 +-
>  drivers/firmware/arm_scmi/driver.c    |    2 +
>  drivers/firmware/arm_scmi/protocols.h |    1 +
>  drivers/firmware/arm_scmi/telemetry.c | 2671 +++++++++++++++++++++++++

Ouch. Might be worth splitting this up into more bite sized pieces.

It's a bit of a take a deep breath before diving in patch at the moment.
So the following is rather superficial.

>  include/linux/scmi_protocol.h         |  188 +-
>  5 files changed, 2862 insertions(+), 2 deletions(-)
>  create mode 100644 drivers/firmware/arm_scmi/telemetry.c
> 



> diff --git a/drivers/firmware/arm_scmi/telemetry.c b/drivers/firmware/arm_scmi/telemetry.c
> new file mode 100644
> index 000000000000..16bcdcdc1dc3
> --- /dev/null
> +++ b/drivers/firmware/arm_scmi/telemetry.c
> @@ -0,0 +1,2671 @@

> +static void scmi_telemetry_free_tde_put(struct telemetry_info *ti,
> +					struct telemetry_de *tde)
> +{
> +	guard(mutex)(&ti->free_mtx);
> +
> +	list_add_tail(&tde->item, &ti->free_des);
> +}

> +static int iter_de_descr_update_state(struct scmi_iterator_state *st,
> +				      const void *response, void *priv)
> +{
> +	const struct scmi_msg_resp_telemetry_de_description *r = response;
> +	struct scmi_tlm_de_priv *p = priv;
> +
> +	st->num_returned = le32_get_bits(r->num_desc, GENMASK(15, 0));
> +	st->num_remaining = le32_get_bits(r->num_desc, GENMASK(31, 16));
> +
> +	/* Initialized to first descriptor */
> +	p->next = (void *)r->desc;

No need to cast to a void *
C always lets you do this implicitly if the target type is a void *.

> +
> +	return 0;
> +}
> +


> +static int scmi_telemetry_initial_state_lookup(struct telemetry_info *ti)
> +{
> +	struct device *dev = ti->ph->dev;
> +	int ret;
> +
> +	ret = scmi_telemetry_config_lookup(ti, SCMI_TLM_GRP_INVALID,
> +					   &ti->info.enabled,
> +					   &ti->info.active_update_interval);
> +	if (ret)
> +		return ret;
> +
> +	if (ti->info.enabled) {

I'd flip logic to reduce indent
	if (!ti->info.enabled)
		return 0;

	/*
	 *...

> +		/*
> +		 * When Telemetry is found already enabled on the platform,
> +		 * proceed with passive discovery using DE_ENABLED_LIST and
> +		 * TCDF scanning: note that this CAN only discover DEs exposed
> +		 * via SHMTIs.
> +		 * FastChannel DEs need a proper DE_DESCRIPTION enumeration,
> +		 * while, even though incoming Notifications could be used for
> +		 * passive discovery too, it would carry a considerable risk
> +		 * of assimilating trash as DEs.
> +		 */
> +		dev_info(dev,
> +			 "Telemetry found enabled with update interval %ux10^%d\n",
> +			 SCMI_TLM_GET_UPDATE_INTERVAL_SECS(ti->info.active_update_interval),
> +			 SCMI_TLM_GET_UPDATE_INTERVAL_EXP(ti->info.active_update_interval));
> +		/*
> +		 * Query enabled DEs list: collect states.
> +		 * It will include DEs from any interface.
> +		 * Enabled groups still NOT enumerated.
> +		 */
> +		ret = scmi_telemetry_enumerate_des_enabled_list(ti);
> +		if (ret)
> +			dev_warn(dev, FW_BUG "Cannot query enabled DE list. Carry-on.\n");
> +
> +		/* Discover DEs on SHMTis: collect states/offsets/values */
> +		for (int id = 0; id < ti->num_shmti; id++) {
> +			ret = scmi_telemetry_shmti_scan(ti, id, 0, SCAN_DISCOVERY);
> +			if (ret)
> +				dev_warn(dev, "Failed discovery-scan of SHMTI ID:%d\n", id);
> +		}
> +	}
> +
> +	return 0;
> +}
}

> +static int iter_intervals_update_state(struct scmi_iterator_state *st,
> +				       const void *response, void *priv)
> +{
> +	const struct scmi_msg_resp_telemetry_update_intervals *r = response;
> +
> +	st->num_returned = le32_get_bits(r->flags, GENMASK(11, 0));
> +	st->num_remaining = le32_get_bits(r->flags, GENMASK(31, 16));
> +
> +	/*
> +	 * total intervals is not declared previously anywhere so we
> +	 * assume it's returned+remaining on first call.
> +	 */
> +	if (!st->max_resources) {
> +		struct scmi_tlm_ivl_priv *p = priv;
> +		bool discrete;
> +		int inum;
> +
> +		discrete = INTERVALS_DISCRETE(r->flags);
> +		/* Check consistency on first call */
> +		if (!discrete && (st->num_returned != 3 || st->num_remaining != 0))
> +			return -EINVAL;
> +
> +		inum = st->num_returned + st->num_remaining;
> +		struct scmi_tlm_intervals *intrvs __free(kfree) =
> +			kzalloc(sizeof(*intrvs) + inum * sizeof(__u32), GFP_KERNEL);

Unless this is going to get more complex, the __free() isn't doing anything useful
as there are no other error paths before the no_free_ptr().

> +		if (!intrvs)
> +			return -ENOMEM;
> +
> +		intrvs->num = inum;
> +		intrvs->discrete = discrete;
> +		st->max_resources = intrvs->num;
> +
> +		*p->intrvs = no_free_ptr(intrvs);
> +	}
> +
> +	return 0;

> +static int
> +scmi_tlm_enumerate_update_intervals(struct telemetry_info *ti,
> +				    struct scmi_tlm_intervals **intervals,
> +				    int grp_id, unsigned int flags)
> +{
> +	struct scmi_iterator_ops ops = {
> +		.prepare_message = iter_intervals_prepare_message,
> +		.update_state = iter_intervals_update_state,
> +		.process_response = iter_intervals_process_response,
> +	};
> +	const struct scmi_protocol_handle *ph = ti->ph;
> +	struct scmi_tlm_ivl_priv ipriv = {
> +		.dev = ph->dev,
> +		.grp_id = grp_id,
> +		.intrvs = intervals,
> +		.flags = flags,
> +	};
> +	void *iter;
> +
> +	iter = ph->hops->iter_response_init(ph, &ops, 0,
> +					    TELEMETRY_LIST_UPDATE_INTERVALS,
> +			     sizeof(struct scmi_msg_telemetry_update_intervals),
This alignment is unusual.  Given the length of that type name I'd do this as:

	iter = ph->hops->iter_response_init(ph, &ops, 0,
		TELEMETRY_LIST_UPDATE_INTERVALS,
		sizeof(struct scmi_msg_telemetry_update_intervals),
		&ipriv);

> +					    &ipriv);
> +	if (IS_ERR(iter))
> +		return PTR_ERR(iter);
> +
> +	return ph->hops->iter_response_run(iter);
> +}

> +static const struct scmi_telemetry_de *
> +scmi_telemetry_de_lookup(const struct scmi_protocol_handle *ph, u32 id)
> +{
> +	struct telemetry_info *ti = ph->get_priv(ph);
> +	struct scmi_telemetry_de *de;
> +
> +	ti->res_get(ti);
> +	de = xa_load(&ti->xa_des, id);
> +	if (!de)
> +		return NULL;
> +
> +	return de;

	return xa_load(&ti->xa_des, id);

> +}


> +static struct payload *
> +scmi_telemetry_nearest_blk_ts(struct telemetry_shmti *shmti,
> +			      struct payload *last_payld)
> +{
> +	struct payload *payld, *bts_payld = NULL;
> +	struct tdcf __iomem *tdcf = shmti->base;
> +	u32 *next;
> +
> +	/* Scan from start of TDCF payloads up to last_payld */
> +	payld = (struct payload *)tdcf->payld;

casting away the __iomem is usualy a bad idea.
Shouldn't a readl or similar be used to get next below.


> +	next = (u32 *)payld;
> +	while (payld < last_payld) {
> +		if (IS_BLK_TS(payld))
> +			bts_payld = payld;
> +
> +		next += USE_LINE_TS(payld) ?
> +			TS_LINE_DATA_PAYLD_WORDS : LINE_DATA_PAYLD_WORDS;
> +		payld = (struct payload *)next;
> +	}
> +
> +	return bts_payld;
> +}
> +
> +static struct telemetry_block_ts *
> +scmi_telemetry_blkts_lookup(struct device *dev, struct xarray *xa_bts,
> +			    struct payload *payld)
> +{
> +	struct telemetry_block_ts *bts;
> +
> +	bts = xa_load(xa_bts, (unsigned long)payld);
> +	if (!bts) {
> +		int ret;
> +
> +		bts = devm_kzalloc(dev, sizeof(*bts), GFP_KERNEL);

I'd not normally expect to see xa_insert using devm allocated memory
because you sort of hand ownership to the xa with that call so I'd expect
on exist we'd see a walk of the xa clearing out everything it is tracking.

> +		if (!bts)
> +			return NULL;
> +
> +		refcount_set(&bts->users, 1);
> +		bts->payld = payld;
> +		bts->xa_bts = xa_bts;
> +		mutex_init(&bts->mtx);
> +		ret = xa_insert(xa_bts, (unsigned long)payld, bts, GFP_KERNEL);
> +		if (ret) {
> +			devm_kfree(dev, bts);
> +			return NULL;
> +		}
> +	}
> +
> +	return bts;
> +}

> +
> +static void scmi_telemetry_tdcf_data_parse(struct telemetry_info *ti,
> +					   struct payload __iomem *payld,
> +					   struct telemetry_shmti *shmti,
> +					   enum scan_mode mode)
> +{
> +	bool ts_valid = TS_VALID(payld);
> +	struct telemetry_de *tde;
> +	bool discovered = false;
> +	u64 val, tstamp = 0;
> +	u32 de_id;
> +
> +	de_id = PAYLD_ID(payld);
> +	/* Is thi DE ID know ? */

That comment needs a rewrite.

> +	tde = scmi_telemetry_tde_lookup(ti, de_id);
> +	if (!tde) {
> +		if (mode != SCAN_DISCOVERY)
> +			return;
> +
> +		/* In SCAN_DISCOVERY mode we allocate new DEs for unknown IDs */
> +		tde = scmi_telemetry_tde_get(ti, de_id);
> +		if (IS_ERR(tde))
> +			return;
> +
> +		tde->de.info->id = de_id;
> +		tde->de.enabled = true;
> +		tde->de.tstamp_enabled = ts_valid;
> +		discovered = true;
> +	}
> +
> +	/* Update DE location refs if requested: normally done only on enable */
> +	if (mode >= SCAN_UPDATE) {
> +		tde->base = shmti->base;
> +		tde->eplg = SHMTI_EPLG(shmti);
> +		tde->offset = (void *)payld - (void *)shmti->base;
> +
> +		dev_dbg(ti->ph->dev,
> +			"TDCF-updated DE_ID:0x%08X - shmti:%pX  offset:%u\n",
> +			tde->de.info->id, tde->base, tde->offset);
> +	}
> +
> +	if (discovered) {
> +		if (scmi_telemetry_tde_register(ti, tde)) {
> +			scmi_telemetry_free_tde_put(ti, tde);
> +			return;
> +		}
> +	}
> +
> +	scoped_guard(mutex, &tde->mtx) {
> +		if (tde->last_magic == shmti->last_magic)
> +			return;
> +	}
> +
> +	/* Data is always valid since we are NOT handling BLK TS lines here */
> +	val = LINE_DATA_GET(&payld->l);
> +	/* Collect the right TS */
> +	if (ts_valid) {
> +		if (USE_LINE_TS(payld)) {
> +			tstamp = LINE_TSTAMP_GET(&payld->tsl);
> +		} else if (USE_BLK_TS(payld)) {
> +			if (!tde->bts) {
> +				/*
> +				 * Scanning a TDCF looking for the nearest
> +				 * previous valid BLK_TS, after having found a
> +				 * USE_BLK_TS() payload, MUST succeed.
> +				 */
> +				tde->bts = scmi_telemetry_blkts_bind(ti->ph->dev,
> +								     shmti, payld,
> +								     &ti->xa_bts);
> +				if (WARN_ON(!tde->bts))
> +					return;
> +			}
> +
> +			tstamp = scmi_telemetry_blkts_read(tde->last_magic,
> +							   tde->bts);
> +		}
> +	}
> +
> +	guard(mutex)(&tde->mtx);
> +	tde->last_magic = shmti->last_magic;
> +	tde->last_val = val;
> +	if (tde->de.tstamp_enabled)

ternary perhaps
	tde->last_ts = tde->de.tstamp_enabled ? tstamp : 0;


> +		tde->last_ts = tstamp;
> +	else
> +		tde->last_ts = 0;
> +}




> +static inline void scmi_telemetry_de_data_fc_read(struct telemetry_de *tde,
> +						  u64 *tstamp, u64 *val)
> +{
> +	struct fc_tsline __iomem *fc = tde->base + tde->offset;
> +
> +	*val = LINE_DATA_GET(fc);
> +	if (tstamp) {
> +		if (tde->de.tstamp_support)
> +			*tstamp = LINE_TSTAMP_GET(fc);
> +		else
> +			*tstamp = 0;

		*tstamp = tde->de.tstam_support ? LINE_TIMESTAMP_GET(fc) : 0;

> +	}
> +}
> +
> +static void scmi_telemetry_scan_update(struct telemetry_info *ti, u64 ts)
> +{
> +	struct telemetry_de *tde;
> +
> +	/* Scan all SHMTIs ... */
> +	for (int id = 0; id < ti->num_shmti; id++) {
> +		int ret;
> +
> +		ret = scmi_telemetry_shmti_scan(ti, id, ts, SCAN_LOOKUP);
> +		if (ret)

Might as well simplify given value of ret only used here.

		if (scmi_telemetry_shmti_scan(ti, id, ts, SCAN_LOOKUP)) {
			dev_warn();

> +			dev_warn(ti->ph->dev,
> +				 "Failed update-scan of SHMTI ID:%d\n", id);
> +	}
> +
> +	if (!ti->info.fc_support)
> +		return;
> +
> +	/* Need to enumerate resources to access fastchannels */
> +	ti->res_get(ti);
> +	list_for_each_entry(tde, &ti->fcs_des, item) {
> +		u64 val, tstamp;
> +
> +		if (!tde->de.enabled)
> +			continue;
> +
> +		scmi_telemetry_de_data_fc_read(tde, &tstamp, &val);
> +
> +		guard(mutex)(&tde->mtx);
> +		tde->last_val = val;
> +		if (tde->de.tstamp_enabled)
> +			tde->last_ts = tstamp;
> +		else
> +			tde->last_ts = 0;
> +	}
> +}
> +
> +/*
> + * TDCF and TS Line Management Notes
> + * ---------------------------------
> + *  (from a chat with ATG)

That's probably not a detail we want in the long term record, nice
and helpful as they are :)


> + *
> + * TCDF Payload Metadata notable bits:
> + *  - Bit[3]: USE BLK Tstamp
> + *  - Bit[2]: USE LINE Tstamp
> + *  - Bit[1]: Tstamp VALID
> + *
> + * CASE_1:
...


> +static int
> +scmi_telemetry_samples_collect(struct telemetry_info *ti, int grp_id,
> +			       int *num_samples,
> +			       struct scmi_telemetry_de_sample *samples)
> +{
> +	struct scmi_telemetry_res_info *rinfo;
> +	int max_samples;
> +
> +	max_samples = *num_samples;
> +	*num_samples = 0;
> +
> +	rinfo = ti->res_get(ti);
> +	for (int i = 0; i < rinfo->num_des; i++) {
> +		struct scmi_telemetry_de *de;
> +		u64 val, tstamp;
> +		int ret;
> +
> +		de = rinfo->des[i];
> +		if (grp_id != SCMI_TLM_GRP_INVALID &&
> +		    (!de->grp || de->grp->info->id != grp_id))
> +			continue;
> +
> +		ret = scmi_telemetry_de_cached_read(ti, de, &tstamp, &val);
> +		if (ret)
> +			continue;
> +
> +		if (*num_samples == max_samples)
> +			return -ENOSPC;
> +
> +		samples[*num_samples].tstamp = tstamp;
> +		samples[*num_samples].val = val;
> +		samples[*num_samples].id = de->info->id;
Maybe worth doing
		samples[(*num_samples)++] = (struct scmi_telemetry_de_sample) {
			.tstamp = tstamp,
			.val = val,
			.id = de->info->id,
		};
so that it is immediately obvious you are filling whole record in (or zeroing
any other fields though not relevant here)

> +
> +		(*num_samples)++;
> +	}
> +
> +	return 0;
> +}

> +
> +static int scmi_telemetry_des_sample_get(const struct scmi_protocol_handle *ph,
> +					 int grp_id, int *num_samples,
> +					 struct scmi_telemetry_de_sample *samples)
> +{
> +	struct telemetry_info *ti = ph->get_priv(ph);
> +	struct scmi_msg_telemetry_config_set *msg;
> +	struct scmi_xfer *t;
> +	bool grp_ignore;
> +	int ret;
> +
> +	if (!ti->info.enabled || !num_samples || !samples)
> +		return -EINVAL;
> +
> +	grp_ignore = grp_id == SCMI_TLM_GRP_INVALID ? true : false;
> +	if (!grp_ignore && grp_id >= ti->info.base.num_groups)
> +		return -EINVAL;
> +
> +	ret = ph->xops->xfer_get_init(ph, TELEMETRY_CONFIG_SET,
> +				      sizeof(*msg), 0, &t);
> +	if (ret)
> +		return ret;
> +
> +	msg = t->tx.buf;
> +	msg->grp_id = grp_id;
> +	msg->control = TELEMETRY_ENABLE;
> +	msg->control |= grp_ignore ? TELEMETRY_SET_SELECTOR_ALL :
> +		TELEMETRY_SET_SELECTOR_GROUP;
> +	msg->control |= TELEMETRY_MODE_SINGLE;
> +	msg->sampling_rate = 0;
> +
> +	ret = ph->xops->do_xfer_with_response(ph, t);
> +	if (!ret) {
> +		struct scmi_msg_resp_telemetry_reading_complete *r = t->rx.buf;

Feels like that type might benefit form a shorter name
		struct scmi_msg_resp_telemetry_rd_comp
maybe?

> +
> +		/* Update cached DEs values from payload */
> +		if (r->num_dwords)
> +			scmi_telemetry_msg_payld_process(ti, r->num_dwords,
> +							 r->dwords, 0);
> +		/* Scan and update SMHTIs and FCs */
> +		scmi_telemetry_scan_update(ti, 0);
> +
> +		/* Collect all last cached values */
> +		ret = scmi_telemetry_samples_collect(ti, grp_id, num_samples,
> +						     samples);
> +	}
> +
> +	ph->xops->xfer_put(ph, t);
> +
> +	return ret;
> +}

> +
> +static int scmi_telemetry_reset(const struct scmi_protocol_handle *ph)
> +{
> +	struct scmi_xfer *t;
> +	int ret;
> +
> +	ret = ph->xops->xfer_get_init(ph, TELEMETRY_RESET, sizeof(u32), 0, &t);
> +	if (ret)
> +		return ret;
> +
> +	put_unaligned_le32(0, t->tx.buf);
> +	ret = ph->xops->do_xfer(ph, t);
> +	if (!ret) {
> +		struct telemetry_info *ti = ph->get_priv(ph);
> +
> +		scmi_telemetry_local_resources_reset(ti);
> +		/* Fetch agaon states state from platform.*/

Not sure what that comment means.

> +		ret = scmi_telemetry_initial_state_lookup(ti);
> +		if (ret)
> +			dev_warn(ph->dev,
> +				 FW_BUG "Cannot retrieve initial state after reset.\n");
> +	}
> +
> +	ph->xops->xfer_put(ph, t);
> +
> +	return ret;
> +}

> +static void *
> +scmi_telemetry_fill_custom_report(const struct scmi_protocol_handle *ph,
> +				  u8 evt_id, ktime_t timestamp,
> +				  const void *payld, size_t payld_sz,
> +				  void *report, u32 *src_id)
> +{
> +	const struct scmi_telemetry_update_notify_payld *p = payld;
> +	struct scmi_telemetry_update_report *r = report;
> +
> +	/* At least sized as an empty notification */
> +	if (payld_sz < sizeof(*p))
> +		return NULL;
> +
> +	r->timestamp = timestamp;
> +	r->agent_id = le32_to_cpu(p->agent_id);
> +	r->status = le32_to_cpu(p->status);
> +	r->num_dwords = le32_to_cpu(p->num_dwords);
> +	/*
> +	 * Allocated dwords and report are sized as max_msg_size, so as
> +	 * to allow for the maximum payload permitted by the configured
> +	 * transport. Overflow is not possible since out-of-size messages
> +	 * are dropped at the transport layer.
> +	 */
> +	if (r->num_dwords)
> +		memcpy(r->dwords, p->array, r->num_dwords * sizeof(u32));

This needs le32 magic as you are copying from an array of those to an array
of unsigned int (if you do this as a memcpy that should be u32 to make the
size explicit).

memcpy_from_le32() should do what you need here.


> +
> +	*src_id = 0;
> +
> +	return r;
> +}


> diff --git a/include/linux/scmi_protocol.h b/include/linux/scmi_protocol.h
> index c6efe4f371ac..d58b81ffd81e 100644
> --- a/include/linux/scmi_protocol.h
> +++ b/include/linux/scmi_protocol.h

> +
> +/**
> + * struct scmi_telemetry_proto_ops - represents the various operations provided
> + *	by SCMI Telemetry Protocol
> + *
> + * @info_get: get the general Telemetry information.
> + * @de_lookup: get a specific DE descriptor from the DE id.
> + * @res_get: get a reference to the Telemetry resources descriptor.
> + * @state_get: retrieve the specific DE or GROUP state.
> + * @state_set: enable/disable the specific DE or GROUP with or without timestamps.
> + * @all_disable: disable ALL DEs or GROUPs.
> + * @collection_configure: choose a sampling rate and enable SHMTI/FC sampling
> + *			  for on demand collection via @de_data_read or async
> + *			  notificatioins for all the enabled DEs.
> + * @de_data_read: on-demand read of a single DE and related optional timestamp:
> + *		  the value will be retrieved at the proper SHMTI offset OR
> + *		  from the dedicated FC area (if supported by that DE).
> + * @des_bulk_read: on-demand read of all the currently enabled DEs, or just
> + *		   the ones belonging to a specific group when provided.
> + * @des_sample_get: on-demand read of all the currently enabled DEs, or just
> + *		    the ones belonging to a specific group when provided.
> + *		    This causes an immediate update platform-side of all the
> + *		    enabled DEs.
> + * @config_get: retrieve current telemetry configuration.
> + * @reset: reset configuration and telemetry data.
> + */
> +struct scmi_telemetry_proto_ops {
> +	const struct scmi_telemetry_info __must_check *(*info_get)
> +		(const struct scmi_protocol_handle *ph);
> +	const struct scmi_telemetry_de __must_check *(*de_lookup)
> +		(const struct scmi_protocol_handle *ph, u32 id);
> +	const struct scmi_telemetry_res_info __must_check *(*res_get)
> +		(const struct scmi_protocol_handle *ph);
> +	int (*state_get)(const struct scmi_protocol_handle *ph,
> +			 u32 id, bool *enabled, bool *tstamp_enabled);
> +	int (*state_set)(const struct scmi_protocol_handle *ph,
> +			 bool is_group, u32 id, bool *enable, bool *tstamp);
> +	int (*all_disable)(const struct scmi_protocol_handle *ph, bool group);
> +	int (*collection_configure)(const struct scmi_protocol_handle *ph,
> +				    unsigned int res_id, bool grp_ignore,
> +				    bool *enable,
> +				    unsigned int *update_interval_ms,
> +				    enum scmi_telemetry_collection *mode);
> +	int (*de_data_read)(const struct scmi_protocol_handle *ph,
> +			    struct scmi_telemetry_de_sample *sample);
> +	int __must_check (*des_bulk_read)(const struct scmi_protocol_handle *ph,

I'm curious. What about this one makes it suitable for a __must_check?
Seems a bit random.

> +					  int grp_id, int *num_samples,
> +					  struct scmi_telemetry_de_sample *samples);
> +	int __must_check (*des_sample_get)(const struct scmi_protocol_handle *ph,
> +					   int grp_id, int *num_samples,
> +					   struct scmi_telemetry_de_sample *samples);
> +	int (*config_get)(const struct scmi_protocol_handle *ph, bool *enabled,
> +			  int *mode, u32 *update_interval);
> +	int (*reset)(const struct scmi_protocol_handle *ph);
> +};

> +
> +struct scmi_telemetry_update_report {
> +	ktime_t		timestamp;
> +	unsigned int	agent_id;
> +	int		status;
> +	unsigned int	num_dwords;
> +	unsigned int	dwords[];

__counted_by not appropriate?

> +};
>  #endif /* _LINUX_SCMI_PROTOCOL_H */

> +	put_unaligned_le32(0, t->tx.buf);
> +	ret = ph->xops->do_xfer(ph, t);

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