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

From: Maulik Shah
Date: Wed Oct 13 2021 - 02:04:44 EST

Hi Stephan,

On 10/8/2021 4:04 PM, Stephan Gerhold wrote:
On Fri, Oct 08, 2021 at 02:45:20PM +0530, Maulik Shah wrote:
On 10/7/2021 11:59 PM, Stephan Gerhold wrote:
On Thu, Oct 07, 2021 at 03:27:26PM +0530, Maulik Shah wrote:
From: Mahesh Sivasubramanian <msivasub@xxxxxxxxxxxxxx>

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@xxxxxxxxxxxxxx>
Signed-off-by: Lina Iyer <ilina@xxxxxxxxxxxxxx>
[mkshah: add subsystem sleep stats, create one file for each stat]
Signed-off-by: Maulik Shah <mkshah@xxxxxxxxxxxxxx>
---
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?

Thanks for checking this on MSM8996. Probably it doesnot have SMEM items
allocated so causes WARNINGs.

Keeping subsystem stats info in SMEM is not limited to only RPMH targets.
Downstream has some RPM targets which also uses SMEM to store
subsystem stats so the driver is kept generic.


Thanks for clarifying. To be honest, I'm not sure if the WARN_ON() in
smem is very useful since this isn't really fundamentally different as
if the entry is not allocated. But at the end all that matters is that
there are no warnings when loading this driver on older targets.


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

Right. on existing upstream RPM targets i can skip to create/get SMEM items
since
they are not guranteed to be present and one should continue to use
rpm_master_stats.c to get subsystem stats. (this uses entirely different
data structure for sleep stats and are not part of RPM data ram/SMEM and are
deprecated in downstream).


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.

I think module loading internally takes care of this.
we're making a direct function call into the qcom_smem driver, so we
already have a hard dependency on qcom_smem.ko being loaded.


The driver can also be built-in and in this case this is not guaranteed.
This actually happened to me when I tried this on MSM8916: I did not get
the WARNINGs because all the qcom_smem_get() just returned -EPROBE_DEFER.
qcom_smem was then probed after qcom_sleep_stats. Of course, the smem
items are not present there anyway so it did not matter.


I see SMEM is in arch init call, Updated in v12 to register driver in late_init by the time SMEM would have probed already and should not need to handle -EPROBE_DEFER.




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?

Good catch. if the subsystem starts after this driver is loaded, the look up
fails during probe and we don't create debugfs file for the subsystem.

one need to unload/load the driver again after sometime in bootup so by that
time all the subsytems (modem, adsp, cdsp, etc) are up and we create debugfs
file for them.

we have downstream fix for this to create the debugfs files irrespective of
look up fails or not. i have plan to add it once the base driver gets
merged.


OK, I don't seem to have any recent Qualcomm platform that actually has
subsystem stats in SMEM so it doesn't bother me. I just wanted to
mention it for reference. :)

Ok updated driver to not use SMEM for RPM based targets for existing upstream targets (when such target goes upstream in future which uses SMEM for subsystem stats we can enable back with new compatible say -v2).

Thanks,
Maulik


Thanks!
Stephan


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