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

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Message-ID: <20240812101148.wpybfhqkd2kponp7@lcpd911>
Date: Mon, 12 Aug 2024 15:41:48 +0530
From: Dhruva Gole <d-gole@...com>
To: 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>, Kevin
 Hilman <khilman@...libre.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

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.


-- 
Best regards,
Dhruva Gole <d-gole@...com>