Re: [PATCH v5 06/12] firmware: arm_scmi: Extend powercap report to include MAI

Cristian Marussi
2026-05-05T20:13:43Z

On Tue, Apr 28, 2026 at 10:09:15AM +0100, Philip Radford wrote:
> Extend scmi_powercap_meas_changed_report to include MAI change
> notifications.
>

Hi

> Signed-off-by: Philip Radford <philip.radford@arm.com>
> ---
> drivers/firmware/arm_scmi/powercap.c | 20 ++++++++++++--------
> include/linux/scmi_protocol.h | 1 +
> 2 files changed, 13 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/firmware/arm_scmi/powercap.c b/drivers/firmware/arm_scmi/powercap.c
> index 1d1188e98d49..b9d50f4e8ae5 100644
> --- a/drivers/firmware/arm_scmi/powercap.c
> +++ b/drivers/firmware/arm_scmi/powercap.c
> @@ -11,6 +11,7 @@
> #include <linux/io.h>
> #include <linux/module.h>
> #include <linux/scmi_protocol.h>
> +#include <linux/stddef.h>
>
> #include <trace/events/scmi.h>
>
> @@ -164,6 +165,7 @@ struct scmi_powercap_meas_changed_notify_payld {
> __le32 agent_id;
> __le32 domain_id;
> __le32 power;
> + __le32 mai;
> };
>
> struct scmi_msg_powercap_cpc {
> @@ -1212,13 +1214,6 @@ static int scmi_powercap_notify(const struct scmi_protocol_handle *ph,
> if (ret)
> return ret;
>
> - if (enable && !low && !high) {
> - dev_err(ph->dev,
> - "Invalid Measurements Notify thresholds: %u/%u\n",
> - low, high);
> - return -EINVAL;
> - }
> -

Ok so you removed this check because now that a notification can be
emitted even only to notify a MAI change, it is possible that the
thresholds are zero and the notification will be emitted anyway due to
a MAI change....BUT you have to review or completely remove the comment
block that precedes this that says:

/*
* Note that we have to pick the most recently configured
* thresholds to build a proper POWERCAP_MEASUREMENTS_NOTIFY
* enable request and we fail, complaining, if no thresholds
* were ever set, since this is an indication the API has been
* used wrongly.
*/

...becasue NOW is no more true and misleading, since you just removed the
fail and complain part...

It would be good to shortly explain in a comment the new possible
scenarios in which notification can be enabled...

> ret = ph->xops->xfer_get_init(ph, message_id,
> sizeof(*notify), 0, &t);
> if (ret)
> @@ -1333,14 +1328,23 @@ scmi_powercap_fill_custom_report(const struct scmi_protocol_handle *ph,
> {
> const struct scmi_powercap_meas_changed_notify_payld *p = payld;
> struct scmi_powercap_meas_changed_report *r = report;
> + const size_t sz_v2 = offsetofend(struct scmi_powercap_meas_changed_notify_payld,
> + power);
> + const size_t sz_v3 = sizeof(*p);

While this is a valid and nice construct, I think is overkill here since
these offsets/sizes will never change at runtime....

...you can just define above a couples of DEFINE that hardcodes the
sizes of the v2 and v3 by using the

#define SZ_V2 (sizeof(struct scmi_powercap_meas_changed_notify_payld))

and
#define SZ_V3 (SZ_V2 - sizeof(__le32))

>
> - if (sizeof(*p) != payld_sz)
> + if (payld_sz != sz_v2 && payld_sz != sz_v3)
> break;
>
> r->timestamp = timestamp;
> r->agent_id = le32_to_cpu(p->agent_id);
> r->domain_id = le32_to_cpu(p->domain_id);
> r->power = le32_to_cpu(p->power);

maybe more clear to simply:

r->mai = 0;
if (payld_sz == SZ_V3 && PROTOCOL_REV_MAJOR(ph->version) >= 0x3)
r->mai = le32_to_cpu(p->mai);

> +
> + if (payld_sz == sz_v3 && PROTOCOL_REV_MAJOR(ph->version) >= 0x3)
> + r->mai = le32_to_cpu(p->mai);
> + else
> + r->mai = 0;
> +
> *src_id = r->domain_id;

Thanks,
Cristian