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

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Message-ID: <ff48b15c-f8ce-b971-c840-81458715d82b@linaro.org>
Date:   Thu, 30 Mar 2023 14:36:29 +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 12:06, Mikko Perttunen wrote:
> 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.

Ok, I see the point.

I'm worried about the semantic of the errors returned, the translation 
from BPMP_EFAULT to EAGAIN and the assumption it is a disabled (may be 
forever) thermal zone.

What does the documentation say for the error msg.rx.ret == -BPMP_EFAULT?



>>> 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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