linux-kernel - Re: [PATCH] firmware: ti_sci: Convert CPU latency constraint from us to ms

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Message-ID: <20250425190803.s7bag5fop7hsxcxe@sliced>
Date: Fri, 25 Apr 2025 14:08:03 -0500
From: Nishanth Menon <nm@...com>
To: Kendall Willis <k-willis@...com>
CC: <kristo@...nel.org>, <ssantosh@...nel.org>, <d-gole@...com>,
        <linux-arm-kernel@...ts.infradead.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] firmware: ti_sci: Convert CPU latency constraint from us
 to ms

On 10:37-20250425, Kendall Willis wrote:
> Fix CPU resume latency constraint units sent to TI SCI firmware.
> CPU latency constraints are set using the PM QoS framework. The PM QoS
> framework uses usecs as the units for latency whereas the device manager
> uses msecs, so a conversion is needed before passing to device manager.
> 

If this is a bug fix (sounds like it), follow the stable kernel rules.

Also please do not expect reviewers in the community know what this
means, I think you intent to point folks to the url
https://software-dl.ti.com/tisci/esd/latest/2_tisci_msgs/pm/lpm.html#tisci-msg-lpm-set-latency-constraint

If so, add the reference to your commit message.


> Signed-off-by: Kendall Willis <k-willis@...com>
> Reviewed-by: Dhruva Gole <d-gole@...com>
> ---
> Test log [1] shows entry to MCU Only low power mode by sending a CPU
> resume latency constraint of 100000 us using PM QoS. MCU Only is shown
> to be entered by 0x1 as the printed mode.
> 
> [1] https://gist.github.com/kwillis01/059a2ca38232387b414bc6f4b87c7475
> ---
>  drivers/firmware/ti_sci.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/firmware/ti_sci.c b/drivers/firmware/ti_sci.c
> index 806a975fff22..bc138a837430 100644
> --- a/drivers/firmware/ti_sci.c
> +++ b/drivers/firmware/ti_sci.c
> @@ -3670,6 +3670,7 @@ static int __maybe_unused ti_sci_suspend(struct device *dev)
>  	struct ti_sci_info *info = dev_get_drvdata(dev);
>  	struct device *cpu_dev, *cpu_dev_max = NULL;
>  	s32 val, cpu_lat = 0;
> +	u16 cpu_lat_ms;
>  	int i, ret;
>  
>  	if (info->fw_caps & MSG_FLAG_CAPS_LPM_DM_MANAGED) {
> @@ -3682,9 +3683,13 @@ static int __maybe_unused ti_sci_suspend(struct device *dev)
>  			}
>  		}
>  		if (cpu_dev_max) {
> -			dev_dbg(cpu_dev_max, "%s: sending max CPU latency=%u\n", __func__, cpu_lat);
> +			/* PM QoS latency unit is usecs, TI SCI uses msecs */
> +			cpu_lat_ms = cpu_lat / USEC_PER_MSEC;

round_down or a round_up? I assume you intent round_down, please
document that in the comments.

> +			dev_dbg(cpu_dev_max, "%s: sending max CPU latency=%u ms\n", __func__,
> +				cpu_lat_ms);
>  			ret = ti_sci_cmd_set_latency_constraint(&info->handle,
> -								cpu_lat, TISCI_MSG_CONSTRAINT_SET);
> +								cpu_lat_ms,
> +								TISCI_MSG_CONSTRAINT_SET);
>  			if (ret)
>  				return ret;
>  		}
> 
> base-commit: 393d0c54cae31317deaa9043320c5fd9454deabc
> -- 
> 2.34.1
> 

-- 
Regards,
Nishanth Menon
Key (0xDDB5849D1736249D) / Fingerprint: F8A2 8693 54EB 8232 17A3  1A34 DDB5 849D 1736 249D