On Thu, 21 Nov 2024, Antheas Kapenekakis wrote:
> Add a sysfs attribute to allow informing the kernel about the current
> standby state, those being: "active", "screen_off", "sleep", and
> "resume" (to prepare turning the display on). The final modern
> standby state DRIPS is omitted, as that is entered during the kernel
> suspend process and userspace will never see it.
>
> Signed-off-by: Antheas Kapenekakis <l...@antheas.dev>
> ---
> Documentation/ABI/testing/sysfs-power | 34 ++++++++++++
> kernel/power/main.c | 75 +++++++++++++++++++++++++++
> 2 files changed, 109 insertions(+)
>
> diff --git a/Documentation/ABI/testing/sysfs-power
> b/Documentation/ABI/testing/sysfs-power
> index a3942b1036e2..eff13980cc7c 100644
> --- a/Documentation/ABI/testing/sysfs-power
> +++ b/Documentation/ABI/testing/sysfs-power
> @@ -39,6 +39,40 @@ Description:
> See Documentation/admin-guide/pm/sleep-states.rst for more
> information.
>
> +What: /sys/power/standby
> +Date: November 2024
> +Contact: Antheas Kapenekakis <l...@antheas.dev>
> +Description:
> + The /sys/power/standby file controls the standby state of the
> + system. Modern S0ix capable systems can enter a set of low power
> + states while the kernel is still active. Transitioning into
> those
> + states may 1) deactivate tertiary hardware, and 2) change the
> + presentation of the device (e.g., pulse the suspend light, turn
> + off the keyboard backlight).
> +
> + Available states are "active" (fully active), "screen-off"
> (fully
> + active but all displays of the system are off; virtual and
> real),
> + "sleep" (major userspace components have been frozen; light
> + background tasks may still run; this state may affect the power
> + envelope of the device). The final state is DRIPS or LSP0, where
> + the kernel suspends, and is entered by writing "mem" to
> + /sys/power/state. There is a secondary sleep state called
> "resume"
> + that can only be entered from "sleep" and is used in certain
> + devices to boost the Power Limit (PLx) while remaining in sleep
> + to hasten preparing for transitioning to "active".
> +
> + Writing one of the above strings to this file causes the system
> + to transition into the corresponding state, by firing the
> + corresponding firmware notifications during the transition.
> +
> + DRIPS or LSP0 (i.e., mem "s2idle") can only be entered from the
> + "sleep" state. If the kernel is asked to transition to DRIPS
> from
> + a different state, it will transition to "sleep" and then
> suspend.
> + On wakeup, the kernel will transition back to the previous
> state.
> +
> + See Documentation/admin-guide/pm/standby-states.rst for more
> + information.
> +
> What: /sys/power/disk
> Date: September 2006
> Contact: Rafael J. Wysocki <r...@rjwysocki.net>
> diff --git a/kernel/power/main.c b/kernel/power/main.c
> index 6254814d4817..4377fdaf4a8d 100644
> --- a/kernel/power/main.c
> +++ b/kernel/power/main.c
> @@ -748,6 +748,80 @@ static ssize_t state_store(struct kobject *kobj, struct
> kobj_attribute *attr,
>
> power_attr(state);
>
> +#ifdef CONFIG_SUSPEND
> +/*
> + * standby - control system s2idle standby state.
> + *
> + * show() returns available standby states, which may be "active",
> "screen_off",
> + * "sleep" and "resume" (still in sleep but preparing to turn on display).
> + * See Documentation/admin-guide/pm/standby-states.rst for a description of
> + * what they mean.
> + *
> + * store() accepts one of those strings, translates it into the proper
> + * enumerated value, and initiates a transition to that standby state.
> + *
> + * When the system suspends, it will first enter the state "sleep", suspend,
> + * and then restore the last state before entering "sleep". I.e., if
> userspace
> + * is not S0ix-aware, the transitions expected by Modern Standby devices will
> + * always be performed.
> + */
> +static ssize_t standby_show(struct kobject *kobj, struct kobj_attribute
> *attr,
> + char *buf)
> +{
> + char *s = buf;
Instead of char *, add size_t len for the offset.
Order these to reverse xmas tree.
> + standby_state_t i;
> + standby_state_t curr = pm_standby_state();
> +
> + if (curr < 0)
> + return -EBUSY;
> +
> + for (i = PM_STANDBY_MIN; i < PM_STANDBY_MAX; i++)
> + if (standby_states[i])
> + s += sprintf(s, curr == i ? "[%s] " : "%s ",
> standby_states[i]);
Do not use sprintf() for anything new.
For sysfs, sysfs_emit_at() (or sysfs_emit()) is the correct function.
You could consider using reverse logic + continue to bring down the
indentation level.
> +
> + if (s != buf)
> + /* convert the last space to a newline */
> + *(s - 1) = '\n';
> + return (s - buf);
> +}
> +
> +static standby_state_t decode_standby_state(const char *buf, size_t n)
> +{
> + standby_state_t state;
> + char *p;
> + int len;
size_t
> + p = memchr(buf, '\n', n);
> + len = p ? p - buf : n;
> +
> + for (state = PM_STANDBY_MIN; state < PM_STANDBY_MAX; state++) {
> + const char *label = standby_states[state];
> +
> + if (label && len == strlen(label) && !strncmp(buf, label, len))
Isn't len == strlen(label) && !strncmp(buf, label, len) same as using just
using !strcmp() ?
> + return state;
> + }
> +
> + return PM_STANDBY_MAX;
> +}
> +
> +static ssize_t standby_store(struct kobject *kobj, struct kobj_attribute
> *attr,
> + const char *buf, size_t n)
> +{
> + int error;
> + standby_state_t state;
> +
> + state = decode_standby_state(buf, n);
> +
> + if (state >= PM_STANDBY_MAX)
> + return -EINVAL;
> +
> + error = pm_standby_transition(state);
> + return error ? error : n;
return error ?: n
> +}
> +
> +power_attr(standby);
> +#endif
> +
> #ifdef CONFIG_PM_SLEEP
> /*
> * The 'wakeup_count' attribute, along with the functions defined in
> @@ -974,6 +1048,7 @@ static struct attribute * g[] = {
> #ifdef CONFIG_SUSPEND
> &mem_sleep_attr.attr,
> &sync_on_suspend_attr.attr,
> + &standby_attr.attr,
> #endif
> #ifdef CONFIG_PM_AUTOSLEEP
> &autosleep_attr.attr,
>
--
i.
