linux-kernel - Re: [PATCH v11 4/4] firmware: ti_sci: add CPU latency constraint management

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Message-ID: <20240903005422.GA4638@thelio-3990X>
Date: Mon, 2 Sep 2024 17:54:22 -0700
From: Nathan Chancellor <nathan@...nel.org>
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>, Dhruva Gole <d-gole@...com>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v11 4/4] firmware: ti_sci: add CPU latency constraint
 management

Hi Markus,

On Thu, Aug 29, 2024 at 10:16:05PM +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>
> Reviewed-by: Dhruva Gole <d-gole@...com>
> Signed-off-by: Dhruva Gole <d-gole@...com>
> Signed-off-by: Kevin Hilman <khilman@...libre.com>
> Tested-by: Dhruva Gole <d-gole@...com>
> Signed-off-by: Markus Schneider-Pargmann <msp@...libre.com>
> ---
>  drivers/firmware/ti_sci.c | 24 +++++++++++++++++++++++-
>  1 file changed, 23 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/firmware/ti_sci.c b/drivers/firmware/ti_sci.c
> index 8482b7077eef..d5d64e5ffbd7 100644
> --- a/drivers/firmware/ti_sci.c
> +++ b/drivers/firmware/ti_sci.c
> @@ -10,6 +10,7 @@
>  #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>
> @@ -20,6 +21,7 @@
>  #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>
> @@ -3669,7 +3671,27 @@ static int ti_sci_prepare_system_suspend(struct ti_sci_info *info)
>  static int __maybe_unused ti_sci_suspend(struct device *dev)
>  {
>  	struct ti_sci_info *info = dev_get_drvdata(dev);
> -	int ret;
> +	struct device *cpu_dev, *cpu_dev_max = NULL;
> +	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);

This change is now in -next as commit 458d22d2e064 ("firmware: ti_sci:
add CPU latency constraint management"), where it breaks the build
when this driver is built as a module because dev_pm_qos_read_value() is
not exported to modules:

  ERROR: modpost: "dev_pm_qos_read_value" [drivers/firmware/ti_sci.ko] undefined!

Obviously exporting it would fix the build but sometimes that is
controversial, hence just the report.

> +			if (val != PM_QOS_RESUME_LATENCY_NO_CONSTRAINT) {
> +				cpu_lat = max(cpu_lat, val);
> +				cpu_dev_max = cpu_dev;
> +			}
> +		}
> +		if (cpu_dev_max) {
> +			dev_dbg(cpu_dev_max, "%s: sending max CPU latency=%u\n", __func__, cpu_lat);
> +			ret = ti_sci_cmd_set_latency_constraint(&info->handle,
> +								cpu_lat, TISCI_MSG_CONSTRAINT_SET);
> +			if (ret)
> +				return ret;
> +		}
> +	}
>  
>  	ret = ti_sci_prepare_system_suspend(info);
>  	if (ret)
> -- 
> 2.45.2
>