Re: [PATCH V2] cpufreq: ARM big LITTLE: Add generic cpufreq driver and its DT glue

On 03/26/2013 10:51 AM, Viresh Kumar wrote:

big LITTLE is ARM's new Architecture focussing power/performance needs of modern world. More information about big LITTLE can be found here:

http://www.arm.com/products/processors/technologies/biglittleprocessing.php http://lwn.net/Articles/481055/

In order to keep cpufreq support for all big LITTLE platforms simple/generic, this patch tries to add a generic cpufreq driver layer for all big LITTLE platforms.

The driver is divided into two parts:

• Core driver: Generic and shared across all big LITTLE SoC's
• Glue drivers: Per platform drivers providing ops to the core driver

This patch adds in a generic glue driver which would extract information from Device Tree.

Future SoC's can either reuse the DT glue or write their own depending on the need.

Signed-off-by: Sudeep KarkadaNagesha sudeep.karkadanagesha@arm.com Signed-off-by: Viresh Kumar viresh.kumar@linaro.org

[...]

diff --git a/drivers/cpufreq/arm_big_little_dt.c b/drivers/cpufreq/arm_big_little_dt.c new file mode 100644 index 0000000..452ff46 --- /dev/null +++ b/drivers/cpufreq/arm_big_little_dt.c @@ -0,0 +1,92 @@ +/*

• • Generic big.LITTLE CPUFreq Interface driver
• • It provides necessary ops to arm_big_little cpufreq driver and gets
• • Frequency information from Device Tree. Freq table in DT must be in KHz.
• • Copyright (C) 2013 Linaro.
• • Viresh Kumar viresh.kumar@linaro.org
• • This program is free software; you can redistribute it and/or modify
• • it under the terms of the GNU General Public License version 2 as
• • published by the Free Software Foundation.
• • This program is distributed "as is" WITHOUT ANY WARRANTY of any
• • kind, whether express or implied; without even the implied warranty
• • of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
• • GNU General Public License for more details.
• */

+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

+#include <linux/cpufreq.h> +#include <linux/device.h> +#include <linux/export.h> +#include <linux/module.h> +#include <linux/of.h> +#include <linux/opp.h> +#include <linux/slab.h> +#include <linux/types.h> +#include "arm_big_little.h"

+static int dt_init_opp_table(struct device *cpu_dev) +{

• struct device_node *np = NULL;
• int count = 0, ret;
• for_each_child_of_node(of_find_node_by_path("/cpus"), np) {

If of_find_node_by_path() returns NULL, there will be a NULL pointer dereference.

• if (count++ != cpu_dev->id)
  

• 	continue;
  

• if (!of_get_property(np, "operating-points", NULL))
  

• 	return -ENODATA;
  

• cpu_dev->of_node = np;
  

• ret = of_init_opp_table(cpu_dev);
  

• if (ret)
  

• 	return ret;
  

• return 0;
  

of_node_put() should be called on np before returning. Also, the reference count of the parent node should be decremented as well.

These comments apply to the below function dt_get_transition_latency() too.

• }
• return -ENODEV;

+}

+static int dt_get_transition_latency(struct device *cpu_dev) +{

• struct device_node *np = NULL;
• u32 transition_latency = CPUFREQ_ETERNAL;
• int count = 0;
• for_each_child_of_node(of_find_node_by_path("/cpus"), np) {

• if (count++ != cpu_dev->id)
  

• 	continue;
  

• of_property_read_u32(np, "clock-latency", &transition_latency);
  

• return 0;
  

• }
• return -ENODEV;

+}

-- Francesco