linux-kernel - Re: [PATCH v10 2/7] ACPI / processor_idle: Add support for Low Power Idle(LPI) states

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Date:	Thu, 21 Jul 2016 15:34:05 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Sudeep Holla <sudeep.holla@....com>
Cc:	ACPI List <linux-acpi@...r.kernel.org>,
	Vikas Sajjan <vikas.cha.sajjan@....com>,
	Sunil <sunil.vl@....com>,
	Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
	PrashanthPrakash <pprakash@...eaurora.org>,
	Al Stone <al.stone@...aro.org>,
	Ashwin Chaugule <ashwin.chaugule@...aro.org>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	LKML <linux-kernel@...r.kernel.org>,
	ALKML <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v10 2/7] ACPI / processor_idle: Add support for Low Power Idle(LPI) states

On Tuesday, July 19, 2016 06:52:54 PM Sudeep Holla wrote:
> ACPI 6.0 introduced an optional object _LPI that provides an alternate
> method to describe Low Power Idle states. It defines the local power
> states for each node in a hierarchical processor topology. The OSPM can
> use _LPI object to select a local power state for each level of processor
> hierarchy in the system. They used to produce a composite power state
> request that is presented to the platform by the OSPM.
> 
> Since multiple processors affect the idle state for any non-leaf hierarchy
> node, coordination of idle state requests between the processors is
> required. ACPI supports two different coordination schemes: Platform
> coordinated and  OS initiated.
> 
> This patch adds initial support for Platform coordination scheme of LPI.
> 
> Cc: "Rafael J. Wysocki" <rjw@...ysocki.net>
> Signed-off-by: Sudeep Holla <sudeep.holla@....com>
> ---
>  drivers/acpi/bus.c              |  14 +-
>  drivers/acpi/processor_driver.c |   2 +-
>  drivers/acpi/processor_idle.c   | 462 +++++++++++++++++++++++++++++++++++-----
>  include/acpi/processor.h        |  24 ++-
>  include/linux/acpi.h            |   4 +
>  5 files changed, 446 insertions(+), 60 deletions(-)
> 

[cut]

> +static int acpi_processor_get_lpi_info(struct acpi_processor *pr)
> +{
> +	int ret, i;
> +	acpi_status status;
> +	acpi_handle handle = pr->handle, pr_ahandle;
> +	struct acpi_device *d = NULL;
> +	struct acpi_lpi_states_array info[2], *tmp, *prev, *curr;
> +
> +	if (!osc_pc_lpi_support_confirmed)
> +		return -EOPNOTSUPP;
> +
> +	if (!acpi_has_method(handle, "_LPI"))
> +		return -EINVAL;
> +
> +	flat_state_cnt = 0;
> +	prev = &info[0];
> +	curr = &info[1];
> +	handle = pr->handle;
> +	ret = acpi_processor_evaluate_lpi(handle, prev);
> +	if (ret)
> +		return ret;
> +	flatten_lpi_states(pr, prev, NULL);
> +
> +	while (ACPI_SUCCESS(status = acpi_get_parent(handle, &pr_ahandle))) {

I should have mentioned that earlier, but forgot, sorry about that.

Assignments under while () etc are generally discouraged as (a) error-prone
and (b) confusing to static analysis tools.

So I'd do

	status = acpi_get_parent(handle, &pr_ahandle);
	while (ACPI_SUCCESS(status)) {

> +		acpi_bus_get_device(pr_ahandle, &d);
> +		handle = pr_ahandle;
> +
> +		if (strcmp(acpi_device_hid(d), ACPI_PROCESSOR_CONTAINER_HID))
> +			break;
> +
> +		/* can be optional ? */
> +		if (!acpi_has_method(handle, "_LPI"))
> +			break;
> +
> +		ret = acpi_processor_evaluate_lpi(handle, curr);
> +		if (ret)
> +			break;
> +
> +		/* flatten all the LPI states in this level of hierarchy */
> +		flatten_lpi_states(pr, curr, prev);
> +
> +		tmp = prev, prev = curr, curr = tmp;


		status = acpi_get_parent(handle, &pr_ahandle);
> +	}
> +

Apart from this the patch looks OK to me, so please only update this one
and I'll queue up the series.

Thanks,
Rafael