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SubjectRe: [v3] soc: qcom: Introduce subsystem sleep stats driver
On Wed 06 Nov 03:19 PST 2019, Maulik Shah wrote:
> diff --git a/Documentation/ABI/testing/sysfs-power b/Documentation/ABI/testing/sysfs-power
> index 6f87b9d..e095eae 100644
> --- a/Documentation/ABI/testing/sysfs-power
> +++ b/Documentation/ABI/testing/sysfs-power
> @@ -288,6 +288,16 @@ Description:
> writing a "0" (default) to it disables them. Reads from
> this file return the current value.
>
> +What: /sys/power/subsystem_sleep/stats
> +Date: December 2017
> +Contact: Maulik Shah <mkshah@codeaurora.org>
> +Description:
> + The /sys/power/subsystem_sleep/stats file prints the subsystem
> + sleep information on Qualcomm Technologies, Inc. (QTI) SoCs.
> +
> + Reading from this file will display subsystem level low power
> + mode statistics.

sysfs files must follow the design of "one file, one value" and it must
be well defined. "sleep information" does not have a defined structure.

And as Stephen has pointed out several times, /sys/power/subsystem_sleep
is hardly the right place for a Qualcomm-specific entry.

[..]
> diff --git a/drivers/soc/qcom/subsystem_sleep_stats.c b/drivers/soc/qcom/subsystem_sleep_stats.c
[..]
> +static int __init subsystem_sleep_stats_init(void)
> +{
> + struct kobject *ss_stats_kobj;
> + int ret;
> +
> + prvdata = kzalloc(sizeof(*prvdata), GFP_KERNEL);
> + if (!prvdata)
> + return -ENOMEM;
> +
> + ss_stats_kobj = kobject_create_and_add("subsystem_sleep",
> + power_kobj);
> + if (!ss_stats_kobj)
> + return -ENOMEM;
> +
> + prvdata->kobj = ss_stats_kobj;
> +
> + sysfs_attr_init(&prvdata->ka.attr);
> + prvdata->ka.attr.mode = 0444;
> + prvdata->ka.attr.name = "stats";
> + prvdata->ka.show = subsystem_stats_show;
> +
> + ret = sysfs_create_file(prvdata->kobj, &prvdata->ka.attr);
> + if (ret) {
> + kobject_put(prvdata->kobj);
> + kfree(prvdata);
> + }
> +
> + return ret;
> +}
> +
> +static void __exit subsystem_sleep_stats_exit(void)
> +{
> + sysfs_remove_file(prvdata->kobj, &prvdata->ka.attr);
> + kobject_put(prvdata->kobj);
> + kfree(prvdata);
> +}
> +
> +module_init(subsystem_sleep_stats_init);
> +module_exit(subsystem_sleep_stats_exit);

In the event that this is compiled as a kernel module, this driver won't
be automatically loaded - there's no references from other drivers nor
devicetree.

But equally big of an issue is that there's a single arm64 defconfig, so
this driver will be available on non-Qualcomm installations as well,
so you will be creating /sys/power/subsystem_sleep/stats regardless if
it ever will be possible to get any data out of this.

Regards,
Bjorn

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