linux-kernel - Re: [PATCH v11 2/5] soc: qcom: Add Sleep stats driver

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Date:   Thu, 7 Oct 2021 20:29:16 +0200
From:   Stephan Gerhold <stephan@...hold.net>
To:     Maulik Shah <mkshah@...eaurora.org>
Cc:     swboyd@...omium.org, mka@...omium.org, evgreen@...omium.org,
        bjorn.andersson@...aro.org, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org, agross@...nel.org,
        dianders@...omium.org, linux@...ck-us.net, rnayak@...eaurora.org,
        lsrao@...eaurora.org,
        Mahesh Sivasubramanian <msivasub@...eaurora.org>,
        Lina Iyer <ilina@...eaurora.org>,
        Yassine Oudjana <y.oudjana@...tonmail.com>
Subject: Re: [PATCH v11 2/5] soc: qcom: Add Sleep stats driver

Hi Maulik,

On Thu, Oct 07, 2021 at 03:27:26PM +0530, Maulik Shah wrote:
> From: Mahesh Sivasubramanian <msivasub@...eaurora.org>
> 
> Let's add a driver to read the stats from remote processor and
> export to debugfs.
> 
> The driver creates "qcom_sleep_stats" directory in debugfs and
> adds files for various low power mode available. Below is sample
> output with command
> 
> cat /sys/kernel/debug/qcom_sleep_stats/ddr
> count = 0
> Last Entered At = 0
> Last Exited At = 0
> Accumulated Duration = 0
> 
> Signed-off-by: Mahesh Sivasubramanian <msivasub@...eaurora.org>
> Signed-off-by: Lina Iyer <ilina@...eaurora.org>
> [mkshah: add subsystem sleep stats, create one file for each stat]
> Signed-off-by: Maulik Shah <mkshah@...eaurora.org>
> ---
>  drivers/soc/qcom/Kconfig            |  10 ++
>  drivers/soc/qcom/Makefile           |   1 +
>  drivers/soc/qcom/qcom_sleep_stats.c | 259 ++++++++++++++++++++++++++++++++++++
>  3 files changed, 270 insertions(+)
>  create mode 100644 drivers/soc/qcom/qcom_sleep_stats.c
> 
> [...]
> +
> +static int qcom_subsystem_sleep_stats_show(struct seq_file *s, void *unused)
> +{
> +	struct subsystem_data *subsystem = s->private;
> +	struct sleep_stats *stat;
> +
> +	/* Items are allocated lazily, so lookup pointer each time */
> +	stat = qcom_smem_get(subsystem->pid, subsystem->smem_item, NULL);
> +	if (IS_ERR(stat))
> +		return -EIO;
> +
> [...]
> +
> +static void qcom_create_subsystem_stat_files(struct dentry *root)
> +{
> +	const struct sleep_stats *stat;
> +	int i;
> +
> +	for (i = 0; i < ARRAY_SIZE(subsystems); i++) {
> +		stat = qcom_smem_get(subsystems[i].pid, subsystems[i].smem_item, NULL);
> +		if (IS_ERR(stat))
> +			continue;
> +
> +		debugfs_create_file(subsystems[i].name, 0400, root, (void *)&subsystems[i],
> +				    &qcom_subsystem_sleep_stats_fops);

This causes WARNINGs on MSM8996 and MSM8916:

[    0.503054] ------------[ cut here ]------------
[    0.503100] WARNING: CPU: 1 PID: 1 at drivers/soc/qcom/smem.c:587 qcom_smem_get+0x184/0x1b0
[    0.503184] CPU: 1 PID: 1 Comm: swapper/0 Not tainted 5.15.0-rc4+ #378
[    0.503218] Hardware name: Xiaomi Mi Note 2 (DT)
[    0.503278] pc : qcom_smem_get+0x184/0x1b0
[    0.503307] lr : qcom_sleep_stats_probe+0xfc/0x20
[    0.503875] Call trace:
[    0.503896]  qcom_smem_get+0x184/0x1b0
[    0.503925]  qcom_sleep_stats_probe+0xfc/0x270

AFAICT from downstream the smem subsystem information is only read in
the rpmh_master_stat.c driver, should this be specific to RPMh?

There is a rpm_master_stat.c too but that looks quite different,
so I guess the approach is different with RPM?

Two more (unrelated) issues here:

  1. This will silently not register anything if SMEM probes after the
     qcom-sleep-stats driver (qcom_smem_get() will return -EPROBE_DEFER)
     and you will just skip registering the debugfs files.

  2. In qcom_subsystem_sleep_stats_show() you say
     /* Items are allocated lazily, so lookup pointer each time */

     But, if the lookup fails here you don't register the debugfs file
     at all. Does this work if the subsystem is started after this driver?

Thanks,
Stephan