linux-kernel - Re: [PATCH v2] thermal: tegra-bpmp: Handle offline zones

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Date:   Thu, 30 Mar 2023 12:03:27 +0200
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Mikko Perttunen <cyndis@...si.fi>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Amit Kucheria <amitk@...nel.org>,
        Zhang Rui <rui.zhang@...el.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>
Cc:     Mikko Perttunen <mperttunen@...dia.com>, linux-pm@...r.kernel.org,
        linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] thermal: tegra-bpmp: Handle offline zones

On 30/03/2023 11:49, 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. When evaluating trips, BPMP will internally
> use -256C as the temperature for offline zones.

> For smooth operation, for offline zones, return -EAGAIN when reading
> the temperature and allow registration of zones even if they are
> offline during probe.

I think it makes more sense to check if the power domain associated with 
the device is powered up and if not return -EPROBE_DEFER.


> Signed-off-by: Mikko Perttunen <mperttunen@...dia.com>
> ---
> v2:
> * Adjusted commit message.
> * Patch 2/2 dropped for now since it is more controversial,
>    and this patch is more critical.
> 
>   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 f5fd4018f72f..4ffc3bb3bf35 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;
>   
> @@ -259,7 +261,12 @@ 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;
>   		}

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