linux-kernel - Re: [PATCH v9 4/4] firmware: ti_sci: add CPU latency constraint management

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Message-ID: <7hfrr9pirh.fsf@baylibre.com>
Date: Mon, 12 Aug 2024 13:51:14 -0700
From: Kevin Hilman <khilman@...libre.com>
To: Dhruva Gole <d-gole@...com>, Markus Schneider-Pargmann <msp@...libre.com>
Cc: Nishanth Menon <nm@...com>, Tero Kristo <kristo@...nel.org>, Santosh
 Shilimkar <ssantosh@...nel.org>, Vibhore Vardhan <vibhore@...com>,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v9 4/4] firmware: ti_sci: add CPU latency constraint
 management

Dhruva Gole <d-gole@...com> writes:

> Hello,
>
> On Aug 09, 2024 at 15:53:47 +0200, Markus Schneider-Pargmann wrote:
>> From: Kevin Hilman <khilman@...libre.com>
>> 
>> During system-wide suspend, check if any of the CPUs have PM QoS
>> resume latency constraints set.  If so, set TI SCI constraint.
>> 
>> TI SCI has a single system-wide latency constraint, so use the max of
>> any of the CPU latencies as the system-wide value.
>> 
>> Note: DM firmware clears all constraints at resume time, so
>> constraints need to be checked/updated/sent at each system suspend.
>> 
>> Co-developed-by: Vibhore Vardhan <vibhore@...com>
>> Signed-off-by: Vibhore Vardhan <vibhore@...com>
>> Signed-off-by: Kevin Hilman <khilman@...libre.com>
>> Reviewed-by: Dhruva Gole <d-gole@...com>
>> Signed-off-by: Dhruva Gole <d-gole@...com>
>> Signed-off-by: Markus Schneider-Pargmann <msp@...libre.com>
>> ---
>>  drivers/firmware/ti_sci.c | 22 +++++++++++++++++++++-
>>  1 file changed, 21 insertions(+), 1 deletion(-)
>> 
>> diff --git a/drivers/firmware/ti_sci.c b/drivers/firmware/ti_sci.c
>> index 5cbeca5df313..481b7649fde1 100644
>> --- a/drivers/firmware/ti_sci.c
>> +++ b/drivers/firmware/ti_sci.c
>> @@ -9,6 +9,7 @@
>>  #define pr_fmt(fmt) "%s: " fmt, __func__
>>  
>>  #include <linux/bitmap.h>
>> +#include <linux/cpu.h>
>>  #include <linux/debugfs.h>
>>  #include <linux/export.h>
>>  #include <linux/io.h>
>> @@ -19,6 +20,7 @@
>>  #include <linux/of.h>
>>  #include <linux/of_platform.h>
>>  #include <linux/platform_device.h>
>> +#include <linux/pm_qos.h>
>>  #include <linux/property.h>
>>  #include <linux/semaphore.h>
>>  #include <linux/slab.h>
>> @@ -3639,7 +3641,25 @@ static int ti_sci_prepare_system_suspend(struct ti_sci_info *info)
>>  static int ti_sci_suspend(struct device *dev)
>>  {
>>  	struct ti_sci_info *info = dev_get_drvdata(dev);
>> -	int ret;
>> +	struct device *cpu_dev;
>> +	s32 val, cpu_lat = 0;
>> +	int i, ret;
>> +
>> +	if (info->fw_caps & MSG_FLAG_CAPS_LPM_DM_MANAGED) {
>> +		for_each_possible_cpu(i) {
>> +			cpu_dev = get_cpu_device(i);
>> +			val = dev_pm_qos_read_value(cpu_dev, DEV_PM_QOS_RESUME_LATENCY);
>> +			if (val != PM_QOS_RESUME_LATENCY_NO_CONSTRAINT)
>> +				cpu_lat = max(cpu_lat, val);
>> +		}
>> +		if (cpu_lat && cpu_lat != PM_QOS_RESUME_LATENCY_NO_CONSTRAINT) {
>> +			dev_dbg(cpu_dev, "%s: sending max CPU latency=%u\n", __func__, cpu_lat);
>
> An interesting observation was made which caused us to suspect this
> code, the CPU on which the latency was actually being set was not being
> printed here. It was always the cpu3
>
> cpu cpu3: ti_sci_suspend: sending max CPU latency=100
>
> If you look at how this print comes, it's always after all the cpu
> indices have run, so by then the cpu_dev value will have always become
> = nproc in the system. This makes debugging it confusing.

Good catch.  That's definitely a debug bug.  :)

Will fix in the next version.

Thanks for the review & testing,

Kevin