linux-kernel - Re: [PATCH v2 5/6] thermal/drivers/mediatek/lvts

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Date:   Fri, 2 Jun 2023 11:17:27 +0200
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Nícolas F. R. A. Prado 
        <nfraprado@...labora.com>
Cc:     kernel@...labora.com, Alexandre Mergnat <amergnat@...libre.com>,
        Balsam CHIHI <bchihi@...libre.com>,
        Chen-Yu Tsai <wenst@...omium.org>,
        Alexandre Bailon <abailon@...libre.com>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        Amit Kucheria <amitk@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Zhang Rui <rui.zhang@...el.com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-mediatek@...ts.infradead.org, linux-pm@...r.kernel.org
Subject: Re: [PATCH v2 5/6] thermal/drivers/mediatek/lvts_thermal: Don't leave
 threshold zeroed

On 04/05/2023 02:48, Nícolas F. R. A. Prado wrote:
> The thermal framework might leave the low threshold unset if there
> aren't any lower trip points. This leaves the register zeroed, which
> translates to a very high temperature for the low threshold. The
> interrupt for this threshold is then immediately triggered, and the
> state machine gets stuck, preventing any other temperature monitoring
> interrupts to ever trigger.
> 
> (The same happens by not setting the Cold or Hot to Normal thresholds
> when using those)
> 
> Set the unused threshold to a valid low value. This value was chosen so
> that for any valid golden temperature read from the efuse, when the
> value is converted to raw and back again to milliCelsius, the result
> doesn't underflow.
> 
> Fixes: f5f633b18234 ("thermal/drivers/mediatek: Add the Low Voltage Thermal Sensor driver")
> Signed-off-by: Nícolas F. R. A. Prado <nfraprado@...labora.com>
> 
> ---
> 
> Changes in v2:
> - Added this commit
> 
>   drivers/thermal/mediatek/lvts_thermal.c | 7 +++++++
>   1 file changed, 7 insertions(+)
> 
> diff --git a/drivers/thermal/mediatek/lvts_thermal.c b/drivers/thermal/mediatek/lvts_thermal.c
> index efd1e938e1c2..951a4cb75ef6 100644
> --- a/drivers/thermal/mediatek/lvts_thermal.c
> +++ b/drivers/thermal/mediatek/lvts_thermal.c
> @@ -82,6 +82,8 @@
>   #define LVTS_HW_SHUTDOWN_MT8195		105000
>   #define LVTS_HW_SHUTDOWN_MT8192		105000
>   
> +#define LVTS_MINIUM_THRESHOLD		20000

MINIMUM

So if the thermal zone reaches 20°C, the interrupt fires, the set_trips 
sets again 20°C but the interrupt won't fire until the temperature goes 
above 20°C and then crosses the temperature low threshold the way down 
again?

>   static int golden_temp = LVTS_GOLDEN_TEMP_DEFAULT;
>   static int coeff_b = LVTS_COEFF_B;
>   
> @@ -309,6 +311,11 @@ static int lvts_set_trips(struct thermal_zone_device *tz, int low, int high)
>   		pr_debug("%s: Setting low limit temperature interrupt: %d\n",
>   			 thermal_zone_device_type(tz), low);
>   		writel(raw_low, LVTS_OFFSETL(base));
> +	} else {
> +		pr_debug("%s: Setting low limit temperature to minimum\n",
> +			 thermal_zone_device_type(tz));
> +		raw_low = lvts_temp_to_raw(LVTS_MINIUM_THRESHOLD);
> +		writel(raw_low, LVTS_OFFSETL(base));

That's duplicate code:

u32 raw_low = lvts_temp_to_raw(low != -INT_MAX ? low : 
LVTS_MINIMUM_THRESHOLD);

And then the condition in the code goes away:
         if (low != -INT_MAX) {
	}

>   	}
>   
>   	/*

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