linux-kernel - Re: [PATCH v5 2/5] ACPI / processor_idle: Add support for Low Power Idle(LPI) states

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Date:	Tue, 17 May 2016 11:46:13 -0600
From:	"Prakash, Prashanth" <pprakash@...eaurora.org>
To:	Sudeep Holla <sudeep.holla@....com>, linux-acpi@...r.kernel.org,
	"Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:	linux-kernel@...r.kernel.org,
	Vikas Sajjan <vikas.cha.sajjan@....com>,
	Sunil <sunil.vl@....com>,
	Ashwin Chaugule <ashwin.chaugule@...aro.org>,
	Al Stone <al.stone@...aro.org>,
	Lorenzo Pieralisi <lorenzo.pieralisi@....com>
Subject: Re: [PATCH v5 2/5] ACPI / processor_idle: Add support for Low Power
 Idle(LPI) states

Hi Sudeep,

On 5/11/2016 9:37 AM, Sudeep Holla wrote:
> +
> +static int acpi_processor_get_lpi_info(struct acpi_processor *pr)
> +{
> +	int ret, i;
> +	struct acpi_lpi_states_array *info;
> +	struct acpi_device *d = NULL;
> +	acpi_handle handle = pr->handle, pr_ahandle;
> +	acpi_status status;
> +
> +	if (!osc_pc_lpi_support_confirmed)
> +		return -EOPNOTSUPP;
> +
> +	max_leaf_depth = 0;
> +	if (!acpi_has_method(handle, "_LPI"))
> +		return -EINVAL;
> +	flat_state_cnt = 0;
> +
> +	while (ACPI_SUCCESS(status = acpi_get_parent(handle, &pr_ahandle))) {
> +		if (!acpi_has_method(handle, "_LPI"))
> +			continue;
> +
> +		acpi_bus_get_device(handle, &d);
> +		if (!strcmp(acpi_device_hid(d), ACPI_PROCESSOR_CONTAINER_HID))
> +			break;
> +
> +		max_leaf_depth++;
> +		handle = pr_ahandle;
> +	}
> +
In the above loop, we break when we find a device with HID == ACPI_PROCESSOR_CONTAINER_HID.
Shouldn't we continue to parse as long as the parent HID == ACPI_PROCESSOR_CONTAINER_HID?
This is required to make sure we parse states in levels higher than cluster level
in processor hierarchy.

Also, I think it might be safe to break out of the loop if we didn't find _LPI
package, instead of continuing. Given  the presence of LPI entry: "Enabled Parent
State", I can't think of a non-ambiguous scenario where we might find LPI packages
in state N and N+2, but not in N+1, as we will not be able to figure out which
state in N enables which states in N+2. Thoughts?

Thanks,
Prashanth