linux-kernel - Re: [PATCH 1/2] thermal: tegra-bpmp: Handle offline zones

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Date:   Wed, 8 Feb 2023 11:31:23 +0100
From:   Thierry Reding <thierry.reding@...il.com>
To:     Mikko Perttunen <cyndis@...si.fi>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Amit Kucheria <amitk@...nel.org>,
        Zhang Rui <rui.zhang@...el.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Srikar Srimath Tirumala <srikars@...dia.com>,
        Mikko Perttunen <mperttunen@...dia.com>,
        Timo Alho <talho@...dia.com>, linux-pm@...r.kernel.org,
        linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] thermal: tegra-bpmp: Handle offline zones

On Tue, Feb 07, 2023 at 03:56:08PM +0200, Mikko Perttunen wrote:
> From: Mikko Perttunen <mperttunen@...dia.com>
> 
> Thermal zones located in power domains may not be accessible when
> the domain is powergated. In this situation, reading the temperature
> will return -BPMP_EFAULT and the temperature is considered to be
> -256C for calculating trips.

Where's that -256C being set? I only see THERMAL_TEMP_INVALID being set
as the default for a zone, but that's not -274C, not -256C. If that's
the temperature that you're referring to, it might be better to state
that we rely on the default temperature rather than any specific number.

Thierry

> 
> For smooth operation, for offline zones, return -EAGAIN when reading
> the temperature and allow registration of zones even if they are
> offline during probe.
> 
> Signed-off-by: Mikko Perttunen <mperttunen@...dia.com>
> ---
>  drivers/thermal/tegra/tegra-bpmp-thermal.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/thermal/tegra/tegra-bpmp-thermal.c b/drivers/thermal/tegra/tegra-bpmp-thermal.c
> index c76e1ea62c8a..628b18818ae9 100644
> --- a/drivers/thermal/tegra/tegra-bpmp-thermal.c
> +++ b/drivers/thermal/tegra/tegra-bpmp-thermal.c
> @@ -52,6 +52,8 @@ static int __tegra_bpmp_thermal_get_temp(struct tegra_bpmp_thermal_zone *zone,
>  	err = tegra_bpmp_transfer(zone->tegra->bpmp, &msg);
>  	if (err)
>  		return err;
> +	if (msg.rx.ret == -BPMP_EFAULT)
> +		return -EAGAIN;
>  	if (msg.rx.ret)
>  		return -EINVAL;
>  
> @@ -257,7 +259,12 @@ static int tegra_bpmp_thermal_probe(struct platform_device *pdev)
>  		zone->tegra = tegra;
>  
>  		err = __tegra_bpmp_thermal_get_temp(zone, &temp);
> -		if (err < 0) {
> +
> +		/*
> +		 * Sensors in powergated domains may temporarily fail to be read
> +		 * (-EAGAIN), but will become accessible when the domain is powered on.
> +		 */
> +		if (err < 0 && err != -EAGAIN) {
>  			devm_kfree(&pdev->dev, zone);
>  			continue;
>  		}
> -- 
> 2.39.0
> 

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