linux-kernel - Re: [PATCH V4 2/2] base/drivers/arch_topology: Default dmips-mhz if they are not set in DT

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Date:   Mon, 26 Nov 2018 19:42:47 -0600
From:   Rob Herring <robh@...nel.org>
To:     Daniel Lezcano <daniel.lezcano@...aro.org>
Cc:     rjw@...ysocki.net, linux-kernel@...r.kernel.org,
        viresh.kumar@...aro.org, Chris Redpath <chris.redpath@...aro.org>,
        Quentin Perret <quentin.perret@...aro.org>,
        Amit Kucheria <amit.kucheria@...aro.org>,
        Nicolas Dechesne <nicolas.dechesne@...aro.org>,
        Niklas Cassel <niklas.cassel@...aro.org>,
        Mark Rutland <mark.rutland@....com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Sudeep Holla <sudeep.holla@....com>,
        Li Yang <leoyang.li@....com>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>
Subject: Re: [PATCH V4 2/2] base/drivers/arch_topology: Default dmips-mhz if
 they are not set in DT

On Mon, Nov 26, 2018 at 01:20:43PM +0100, Daniel Lezcano wrote:
> In the case of asymmetric SoC with the same micro-architecture, we
> have a group of CPUs with smaller OPPs than the other group. One
> example is the 96boards dragonboard 820c. There is no dmips/MHz
> difference between both groups, so no need to specify the values in
> the DT. Unfortunately, without these defined, there is no scaling
> capacity computation triggered, so we need to write
> 'capacity-dmips-mhz' for each CPU with the same value in order to
> force the scaled capacity computation.
> 
> In order to fix this situation, allocate 'raw_capacity' so the pointer
> is set and the init_cpu_capacity_callback() function can be called.
> 
> This was tested on db820c:
>  - specified values in the DT (correct results)
>  - partial values defined in the DT (error + fallback to defaults)
>  - no specified values in the DT (correct results)
> 
> correct results are:
>   cat /sys/devices/system/cpu/cpu*/cpu_capacity
>    758
>    758
>   1024
>   1024
> 
>   ... respectively for CPU0, CPU1, CPU2 and CPU3.
> 
> That reflects the capacity for the max frequencies 1593600 and 2150400.
> 
> Cc: Chris Redpath <chris.redpath@...aro.org>
> Cc: Quentin Perret <quentin.perret@...aro.org>
> Cc: Viresh Kumar <viresh.kumar@...aro.org>
> Cc: Amit Kucheria <amit.kucheria@...aro.org>
> Cc: Nicolas Dechesne <nicolas.dechesne@...aro.org>
> Cc: Niklas Cassel <niklas.cassel@...aro.org>
> Reviewed-by: Viresh Kumar <viresh.kumar@...aro.org>
> Signed-off-by: Daniel Lezcano <daniel.lezcano@...aro.org>
> ---
>  Documentation/devicetree/bindings/arm/cpu-capacity.txt |  6 ++++++

Acked-by: Rob Herring <robh@...nel.org>

>  drivers/base/arch_topology.c                           | 13 ++++++++++++-
>  2 files changed, 18 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/devicetree/bindings/arm/cpu-capacity.txt b/Documentation/devicetree/bindings/arm/cpu-capacity.txt
> index 84262cd..f53a3c9 100644
> --- a/Documentation/devicetree/bindings/arm/cpu-capacity.txt
> +++ b/Documentation/devicetree/bindings/arm/cpu-capacity.txt
> @@ -54,6 +54,12 @@ fall back to the default capacity value for every CPU. If cpufreq is not
>  available, final capacities are calculated by directly using capacity-dmips-
>  mhz values (normalized w.r.t. the highest value found while parsing the DT).
>  
> +If capacity-dmips-mhz is not specified or if the parsing fails, the
> +default capacity value will be computed against the highest frequency.
> +When all CPUs have the same OPP, they will have the same capacity
> +value otherwise the capacity will be scaled down for CPUs having lower
> +frequencies.
> +
>  ===========================================
>  4 - Examples
>  ===========================================
> diff --git a/drivers/base/arch_topology.c b/drivers/base/arch_topology.c
> index fd5325b..e0c5b60 100644
> --- a/drivers/base/arch_topology.c
> +++ b/drivers/base/arch_topology.c
> @@ -243,9 +243,20 @@ static int __init register_cpufreq_notifier(void)
>  	 * until we have the necessary code to parse the cpu capacity, so
>  	 * skip registering cpufreq notifier.
>  	 */
> -	if (!acpi_disabled || !raw_capacity)
> +	if (!acpi_disabled)
>  		return -EINVAL;
>  
> +	if (!raw_capacity) {
> +
> +		pr_info("cpu_capacity: No capacity defined in DT, set default "
> +		       "values to %ld\n", SCHED_CAPACITY_SCALE);
> +
> +		raw_capacity = kmalloc_array(num_possible_cpus(),
> +					     sizeof(*raw_capacity), GFP_KERNEL);
> +		if (!raw_capacity)
> +			return -ENOMEM;
> +	}
> +
>  	if (!alloc_cpumask_var(&cpus_to_visit, GFP_KERNEL)) {
>  		pr_err("cpu_capacity: failed to allocate memory for cpus_to_visit\n");
>  		return -ENOMEM;
> -- 
> 2.7.4
>