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

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Date:   Thu, 30 Mar 2023 13:06:06 +0300
From:   Mikko Perttunen <cyndis@...si.fi>
To:     Daniel Lezcano <daniel.lezcano@...aro.org>,
        "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 3/30/23 13:03, Daniel Lezcano wrote:
> 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.

The power domains in question are related to computer vision engines 
that only get powered on when in use, possibly never if the user doesn't 
run a computer vision workload on the system. We still want other 
thermal zones to be available.

Mikko

> 
> 
>> 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;
>>           }
>