Re: [PATCH v3] PM / devfreq: Add debugfs support with devfreq_summary file

From: Dmitry Osipenko
Date: Mon Jan 13 2020 - 21:52:38 EST

14.01.2020 05:23, Chanwoo Choi ÐÐÑÐÑ:
> On 1/14/20 10:45 AM, Dmitry Osipenko wrote:
>> 14.01.2020 04:45, Chanwoo Choi ÐÐÑÐÑ:
>>> 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. Otherwise, show 'null'.
>>> - 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]
>>> $ 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 null simple_ondemand 0 165000000 165000000 825000000
>>> soc:bus_wcore devfreq1 null 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 333000000 83250000 333000000
>>> soc:bus_g2d_acp devfreq10 devfreq1 passive 0 266000000 66500000 266000000
>>> soc:bus_jpeg devfreq11 devfreq1 passive 0 300000000 75000000 300000000
>>> soc:bus_jpeg_apb devfreq12 devfreq1 passive 0 166500000 83250000 166500000
>>> soc:bus_disp1_fimd devfreq13 devfreq1 passive 0 200000000 120000000 200000000
>>> soc:bus_disp1 devfreq14 devfreq1 passive 0 300000000 120000000 300000000
>>> soc:bus_gscl_scaler devfreq15 devfreq1 passive 0 300000000 150000000 300000000
>>> soc:bus_mscl devfreq16 devfreq1 passive 0 666000000 84000000 666000000
>>>
>>> [lkp: Reported the build error]
>>> Reported-by: kbuild test robot <lkp@xxxxxxxxx>
>>> Signed-off-by: Chanwoo Choi <cw00.choi@xxxxxxxxxxx>
>>> ---
>>> Changes from v2:
>>> - Show 'null' at 'parent_dev' field when governor of devfreq device
>>> is not passive
>>> Changes from v1:
>>> - Drop the patch about 'devfreq_transitions' debugfs file
>>> - Modify from 'hz' to 'Hz'
>>> - Edit the indentation of 'devfreq_summary' when show summary
>>> - Exchange sequence between PTR_ERR and IS_ERR when debugfs_create_dir
>>>
>>> drivers/devfreq/devfreq.c | 84 +++++++++++++++++++++++++++++++++++++++
>>> 1 file changed, 84 insertions(+)
>>>
>>> diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
>>> index 89260b17598f..c5ef2d194b1b 100644
>>> --- a/drivers/devfreq/devfreq.c
>>> +++ b/drivers/devfreq/devfreq.c
>>> @@ -10,6 +10,7 @@
>>> #include <linux/kernel.h>
>>> #include <linux/kmod.h>
>>> #include <linux/sched.h>
>>> +#include <linux/debugfs.h>
>>> #include <linux/errno.h>
>>> #include <linux/err.h>
>>> #include <linux/init.h>
>>> @@ -33,6 +34,7 @@
>>> #define HZ_PER_KHZ 1000
>>>
>>> static struct class *devfreq_class;
>>> +static struct dentry *devfreq_debugfs;
>>>
>>> /*
>>> * devfreq core provides delayed work based load monitoring helper
>>> @@ -1643,6 +1645,79 @@ static struct attribute *devfreq_attrs[] = {
>>> };
>>> ATTRIBUTE_GROUPS(devfreq);
>>>
>>> +/**
>>> + * devfreq_summary_show() - Show the summary of the devfreq devices
>>> + * @s: seq_file instance to show the summary of devfreq devices
>>> + * @data: not used
>>> + *
>>> + * Show the summary of the devfreq devices via 'devfreq_summary' debugfs file.
>>> + * It helps that user can know the detailed information of the devfreq devices.
>>> + *
>>> + * Return 0 always because it shows the information without any data change.
>>> + */
>>> +static int devfreq_summary_show(struct seq_file *s, void *data)
>>> +{
>>> + struct devfreq *devfreq;
>>> + struct devfreq *p_devfreq = NULL;

Looks like there is no need to pre-initialize the p_devfreq, please see
below.

>>> + unsigned long cur_freq, min_freq, max_freq;
>>> + unsigned int polling_ms;
>>> +
>>> + seq_printf(s, "%-30s %-10s %-10s %-15s %10s %12s %12s %12s\n",
>>> + "dev_name",
>>> + "dev",
>>> + "parent_dev",
>>> + "governor",
>>> + "polling_ms",
>>> + "cur_freq_Hz",
>>> + "min_freq_Hz",
>>> + "max_freq_Hz");
>>> + seq_printf(s, "%30s %10s %10s %15s %10s %12s %12s %12s\n",
>>> + "------------------------------",
>>> + "----------",
>>> + "----------",
>>> + "---------------",
>>> + "----------",
>>> + "------------",
>>> + "------------",
>>> + "------------");
>>> +
>>> + mutex_lock(&devfreq_list_lock);
>>> +
>>> + list_for_each_entry_reverse(devfreq, &devfreq_list, node) {
>>> + if (!strncmp(devfreq->governor_name, DEVFREQ_GOV_PASSIVE,
>>> + DEVFREQ_NAME_LEN)) {
>>> + struct devfreq_passive_data *data = devfreq->data;
>>> +
>>> + if (data)
>>> + p_devfreq = data->parent;

else
p_devfreq = NULL;

Otherwise p_devfreq will be reused from a previous devfreq device if
that device has the data->parent.

>>> + } else {
>>> + p_devfreq = NULL;
>>> + }
>>> +
>>> + mutex_lock(&devfreq->lock);
>>> + cur_freq = devfreq->previous_freq,
>>> + get_freq_range(devfreq, &min_freq, &max_freq);
>>> + polling_ms = devfreq->profile->polling_ms,
>>> + mutex_unlock(&devfreq->lock);
>>> +
>>> + seq_printf(s,
>>> + "%-30s %-10s %-10s %-15s %10d %12ld %12ld %12ld\n",
>>> + dev_name(devfreq->dev.parent),
>>> + dev_name(&devfreq->dev),
>>> + p_devfreq ? dev_name(&p_devfreq->dev) : "null",
>>> + devfreq->governor_name,
>>> + polling_ms,
>>> + cur_freq,
>>> + min_freq,
>>> + max_freq);
>>> + }
>>> +
>>> + mutex_unlock(&devfreq_list_lock);
>>> +
>>> + return 0;
>>> +}
>>> +DEFINE_SHOW_ATTRIBUTE(devfreq_summary);
>>> +
>>> static int __init devfreq_init(void)
>>> {
>>> devfreq_class = class_create(THIS_MODULE, "devfreq");
>>> @@ -1659,6 +1734,15 @@ static int __init devfreq_init(void)
>>> }
>>> devfreq_class->dev_groups = devfreq_groups;
>>>
>>> +
>> If you'll you'll take a look at [2], you may notice notice that it
>> checks whether devfreq_debugfs IS_ERR [3] and then bails out.
>>
>> [2] https://protect2.fireeye.com/url?k=a5047d02-f8ca7cd1-a505f64d-000babff317b-ed64c541cd573190&u=https://elixir.bootlin.com/linux/v5.5-rc6/source/fs/debugfs/inode.c#L432
>> [3] https://protect2.fireeye.com/url?k=0a43fffa-578dfe29-0a4274b5-000babff317b-1c1c1062bfaeb0fc&u=https://elixir.bootlin.com/linux/v5.5-rc6/source/fs/debugfs/inode.c#L316
>>
>> Thus you could simply remove the above error handling, making code to
>> look cleaner.
>>
>>
>
> OK. I'll modify it as following: Do you agree?

Looks good, thanks.

> devfreq_debugfs = debugfs_create_dir("devfreq", NULL);

I'd also add a newline here, to ease reading of the code.

> debugfs_create_file("devfreq_summary", 0444,
> devfreq_debugfs, NULL,
> &devfreq_summary_fops);
>
>