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

From: Chanwoo Choi
Date: Mon Jan 13 2020 - 22:55:33 EST

On 1/14/20 11:51 AM, Dmitry Osipenko wrote:
> 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 IS_ENABLED(CONFIG_DEVFREQ_GOV_PASSIVE)

>>>> + 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.

This path has the problem. I'm missing that.

'struct devfreq_passive_data' is only defined
when CONFIG_DEVFREQ_GOV_PASSIVE is enabled.

In case of when CONFIG_DEVFREQ_GOV_PASSIVE is disabled,
p_devfreq should be initialized with NULL as following:
I'll modify this patch as following:

struct devfreq *p_devfreq = NULL;

#if IS_ENABLED(CONFIG_DEVFREQ_GOV_PASSIVE)
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;
#endif


>
>>>> + } 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.

ok.

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


--
Best Regards,
Chanwoo Choi
Samsung Electronics