linux-kernel - Re: [PATCH RESEND v3 3/9] thermal/drivers/mediatek/lvts: Guard against zero temp_factor in lvts_raw_to

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Message-Id: <20251113161859.280743-1-laura.nao@collabora.com>
Date: Thu, 13 Nov 2025 17:18:59 +0100
From: Laura Nao <laura.nao@...labora.com>
To: daniel.lezcano@...aro.org
Cc: andrew-ct.chen@...iatek.com,
	angelogioacchino.delregno@...labora.com,
	arnd@...db.de,
	bchihi@...libre.com,
	colin.i.king@...il.com,
	conor+dt@...nel.org,
	devicetree@...r.kernel.org,
	frank-w@...lic-files.de,
	fshao@...omium.org,
	kernel@...labora.com,
	krzk+dt@...nel.org,
	lala.lin@...iatek.com,
	laura.nao@...labora.com,
	linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	linux-mediatek@...ts.infradead.org,
	linux-pm@...r.kernel.org,
	lukasz.luba@....com,
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	rui.zhang@...el.com,
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	wenst@...omium.org
Subject: Re: [PATCH RESEND v3 3/9] thermal/drivers/mediatek/lvts: Guard against zero temp_factor in lvts_raw_to_temp

Hi Daniel,

On 11/10/25 13:42, Daniel Lezcano wrote:
> On 10/16/25 16:21, Laura Nao wrote:
>> Add a guard against zero temp_factor in lvts_raw_to_temp() to prevent
>> division by zero and ensure safe conversion. 
>
> Is the temp_factor something else than a ro data statically initialized by the lvts_data structure ?
>
> It is pointless to handle the case where the temp_factor is zero. If we read the temperature the kernel crashes immediately (which means it was not tested).
>
> The temp_factor is an internal value of the driver. If the temp_factor is zero, the driver is buggy and should be fixed.
>
>

That’s right - if temp_factor is zero, that indicates broken platform 
data. I propose failing the probe instead of adding a runtime guard, 
since this condition should never happen in a valid configuration. This 
way, we make the developer aware of the issue early and avoid a kernel 
crash at runtime.

I'll send out a v4 to drop the "if (temp_factor == 0)" checks and 
replace the warning with an error:

if (!lvts_data->temp_factor)
	return dev_err_probe(dev, -EINVAL, "temp_factor should never be zero; check platform data.\n");

Best,

Laura

>> Fixes: 6725a29321e4 ("thermal/drivers/mediatek/lvts_thermal: Make coeff configurable")
>> Reviewed-by: Chen-Yu Tsai <wenst@...omium.org>
>> Reviewed-by: Fei Shao <fshao@...omium.org>
>> Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
>> Tested-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
>> Signed-off-by: Laura Nao <laura.nao@...labora.com>
>> ---
>>   drivers/thermal/mediatek/lvts_thermal.c | 12 +++++++++---
>>   1 file changed, 9 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/thermal/mediatek/lvts_thermal.c b/drivers/thermal/mediatek/lvts_thermal.c
>> index 1c54d0b75b1a..4ef549386add 100644
>> --- a/drivers/thermal/mediatek/lvts_thermal.c
>> +++ b/drivers/thermal/mediatek/lvts_thermal.c
>> @@ -284,11 +284,14 @@ static int lvts_raw_to_temp(u32 raw_temp, int temp_factor)
>>     static u32 lvts_temp_to_raw(int temperature, int temp_factor)
>>   {
>> -    u32 raw_temp = ((s64)(golden_temp_offset - temperature)) << 14;
>> +    u32 raw_temp;
>>   -    raw_temp = div_s64(raw_temp, -temp_factor);
>> +    if (temp_factor == 0)
>> +        return temperature;
>>   -    return raw_temp;
>> +    raw_temp = ((s64)(golden_temp_offset - temperature)) << 14;
>> +
>> +    return div_s64(raw_temp, -temp_factor);
>>   }
>>     static int lvts_get_temp(struct thermal_zone_device *tz, int *temp)
>> @@ -1346,6 +1349,9 @@ static int lvts_probe(struct platform_device *pdev)
>>       if (irq < 0)
>>           return irq;
>>   +    if (!lvts_data->temp_factor)
>> +        dev_warn(dev, "temp_factor should never be zero; check platform data.\n");
>> +
>>       golden_temp_offset = lvts_data->temp_offset;
>>         ret = lvts_domain_init(dev, lvts_td, lvts_data); 
> If
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