Re: [PATCH v2] rtc: ab-eoz9: fix negative temperature readings

[sashiko-bot@kernel.org]

> The temperature register is coded with an offset of ABEOZ953_TEMP_MIN
> (-60 degrees C), so the driver computes "raw + ABEOZ953_TEMP_MIN".
> regmap_read() hands the raw value back in an unsigned int, which makes
> that addition - and the multiplication by 1000 that follows - unsigned as
> well: -60 becomes 0xffffffc4 and 1000 * (raw - 60) wraps around for every
> raw value below 60.
> 
> On 64-bit systems the wrapped unsigned int is then zero-extended into the
> long hwmon attribute, so every temperature below 0 degrees C is reported
> as a huge positive value: raw 0 (the -60 degrees C code) becomes
> 4294907296 instead of -60000, raw 30 (-30 degrees C) becomes 4294937296
> instead of -30000.  This also contradicts temp1_min, which the same
> driver reports as -60000, and consumers that only look for negative
> values (thermal governors, monitoring daemons) do not discard the bogus
> value.
> 
> Perform the arithmetic on a signed value.
> 
> Fixes: 67075b63cce2 ("rtc: add AB-RTCMC-32.768kHz-EOZ9 RTC support")
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Yuehong Wu <wuyuehong@cmss.chinamobile.com>

Sashiko has reviewed this patch and found no issues.

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Sashiko AI review · https://sashiko.dev/#/patchset/20261109-rtc-ab-eoz9-neg-temp-v2-1-yuehongwu@cmss.chinamobile.com?part=1