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

[Dmitry Osipenko]

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;
> +	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;
> +		}
> +
> +		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;
>  
> +	devfreq_debugfs = debugfs_create_dir("devfreq", NULL);
> +	if (IS_ERR(devfreq_debugfs) && PTR_ERR(devfreq_debugfs) != -ENODEV) {
> +		pr_warn("%s: couldn't create debugfs dir\n", __FILE__);

If you'll take a look at [1], you may notice that it could fail only in
a single place in the code and in that case the error message is already
printed.

[1] https://elixir.bootlin.com/linux/v5.5-rc6/source/fs/debugfs/inode.c#L543

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

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://elixir.bootlin.com/linux/v5.5-rc6/source/fs/debugfs/inode.c#L432
[3] 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.