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SubjectRe: [PATCH 1/2] PM / devfreq: Add debugfs support with devfreq_summary file
On Tue 07 Jan 01:05 PST 2020, Chanwoo Choi wrote:

> Add debugfs interface to provide debugging information of devfreq device.
> It contains 'devfreq_summary' entry to show the summary of registered
> devfreq devices as following and the additional debugfs file will be added.
> - /sys/kernel/debug/devfreq/devfreq_summary
>
> [Detailed description of each field of 'devfreq_summary' debugfs file]
> - dev_name : Device name of h/w.
> - dev : Device name made by devfreq core.
> - parent_dev : If devfreq device uses the passive governor,
> show parent devfreq device name.
> - governor : Devfreq governor.
> - polling_ms : If devfreq device uses the simple_ondemand governor,
> polling_ms is necessary for the period. (unit: millisecond)
> - cur_freq_hz : Current Frequency (unit: hz)
> - old_freq_hz : Frequency before changing. (unit: hz)
> - new_freq_hz : Frequency after changed. (unit: hz)
>
> [For example on Exynos5422-based Odroid-XU3 board]
> - In order to show the multiple governors on devfreq_summay result,
> change the governor of devfreq0 from simple_ondemand to userspace.
>
> $ cat /sys/kernel/debug/devfreq/devfreq_summary
> dev_name dev parent_dev governor polling_ms cur_freq_hz min_freq_hz max_freq_hz
> ------------------------------ ---------- ---------- --------------- ---------- ------------ ------------ ------------
> 10c20000.memory-controller devfreq0 userspace 0 206000000 165000000 825000000
> soc:bus_wcore devfreq1 simple_ondemand 50 532000000 88700000 532000000
> soc:bus_noc devfreq2 devfreq1 passive 0 111000000 66600000 111000000
> soc:bus_fsys_apb devfreq3 devfreq1 passive 0 222000000 111000000 222000000
> soc:bus_fsys devfreq4 devfreq1 passive 0 200000000 75000000 200000000
> soc:bus_fsys2 devfreq5 devfreq1 passive 0 200000000 75000000 200000000
> soc:bus_mfc devfreq6 devfreq1 passive 0 333000000 83250000 333000000
> soc:bus_gen devfreq7 devfreq1 passive 0 266000000 88700000 266000000
> soc:bus_peri devfreq8 devfreq1 passive 0 66600000 66600000 66600000
> soc:bus_g2d devfreq9 devfreq1 passive 0 0 83250000 333000000
> soc:bus_g2d_acp devfreq10 devfreq1 passive 0 0 66500000 266000000
> soc:bus_jpeg devfreq11 devfreq1 passive 0 0 75000000 300000000
> soc:bus_jpeg_apb devfreq12 devfreq1 passive 0 0 83250000 166500000
> soc:bus_disp1_fimd devfreq13 devfreq1 passive 0 0 120000000 200000000
> soc:bus_disp1 devfreq14 devfreq1 passive 0 0 120000000 300000000
> soc:bus_gscl_scaler devfreq15 devfreq1 passive 0 0 150000000 300000000
> soc:bus_mscl devfreq16 devfreq1 passive 0 0 84000000 666000000

This looks quite useful.

>
> Reported-by: kbuild test robot <lkp@intel.com>

May I ask how the build test robot came up with this idea?

> Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>
> ---
> drivers/devfreq/devfreq.c | 80 +++++++++++++++++++++++++++++++++++++++
> 1 file changed, 80 insertions(+)
>
> diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
[..]
> +/**
> + * devfreq_summary_show() - Show the summary of the registered devfreq devices
> + * via 'devfreq_summary' debugfs file.

Please make this proper kerneldoc, i.e:

* func() - short description
* @s:
* @data:
*
* Long description
*
* Return: foo on bar

[..]
> @@ -1733,6 +1803,16 @@ static int __init devfreq_init(void)
> }
> devfreq_class->dev_groups = devfreq_groups;
>
> + devfreq_debugfs = debugfs_create_dir("devfreq", NULL);
> + if (PTR_ERR(devfreq_debugfs) != -ENODEV && IS_ERR(devfreq_debugfs)) {

Don't PTR_ERR() before IS_ERR().

> + devfreq_debugfs = NULL;

I don't think you need this, given that debugfs_create_file() will fail
gracefully when passed and IS_ERR()

> + pr_warn("%s: couldn't create debugfs dir\n", __FILE__);

Afaict debugfs_create_() won't fail without printing a message already.

> + } else {
> + debugfs_create_file("devfreq_summary", 0444,
> + devfreq_debugfs, NULL,
> + &devfreq_summary_fops);
> + }
> +
> return 0;
> }
> subsys_initcall(devfreq_init);

Regards,
Bjorn

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