From: Svyatoslav Ryhel clamor95@gmail.com
[ Upstream commit d055f51731744243b244aafb1720f793a5b61f7b ]
IIO thermal channel is in millidegree while power supply framework expects decidegree values. Adjust scaling to get correct readings.
Signed-off-by: Svyatoslav Ryhel clamor95@gmail.com Link: https://lore.kernel.org/r/20250430060239.12085-2-clamor95@gmail.com Signed-off-by: Sebastian Reichel sebastian.reichel@collabora.com Signed-off-by: Sasha Levin sashal@kernel.org ---
**YES** This commit should be backported to stable kernel trees. Here's my extensive analysis: ## Code Analysis The commit fixes a **units conversion bug** in the max17040 power supply driver's temperature reporting. Specifically: ### The Problem The original code in `max17040_get_property()` for `POWER_SUPPLY_PROP_TEMP` was: ```c iio_read_channel_processed_scale(chip->channel_temp, &val->intval, 10); ``` ### The Fix The corrected code is: ```c iio_read_channel_processed(chip->channel_temp, &val->intval); val->intval /= 100; /bin /bin.usr-is-merged /boot /dev /etc /home /init /lib /lib.usr-is-merged /lib64 /lost+found /media /mnt /opt /proc /root /run /sbin /sbin.usr-is-merged /snap /srv /sys /tmp /usr /var Convert from milli- to deci-degree model/ prompt/ src/ target/ ``` ### Units Mismatch Issue According to the power supply class documentation found in `/home/sasha/linux/Documentation/power/power_supply_class.rst`: > "All voltages, currents, charges, energies, time and **temperatures** in µV, µA, µAh, µWh, seconds and **tenths of degree Celsius** unless otherwise stated." The power supply framework expects temperatures in **tenths of degree Celsius** (decidegrees), but IIO thermal channels typically return values in **millidegrees Celsius**. ### Mathematical Analysis - IIO thermal channel: returns millidegrees (1/1000 °C) - Power supply framework expects: decidegrees (1/10 °C) - Required conversion: millidegrees ÷ 100 = decidegrees - Old code: Applied a scale of 10, which would convert from decidegrees to degrees (wrong direction) - New code: Divides by 100, correctly converting from millidegrees to decidegrees ### Confirmation from Kernel Sources Looking at `max17042_battery.c` (similar chip), line 109 shows the correct pattern: ```c /bin /bin.usr-is-merged /boot /dev /etc /home /init /lib /lib.usr- is-merged /lib64 /lost+found /media /mnt /opt /proc /root /run /sbin /sbin.usr-is-merged /snap /srv /sys /tmp /usr /var The value is converted into deci-centigrade scale model/ prompt/ src/ target/ *temp = *temp 0001-Fix-Clippy-warnings.patch 0002-Enhance-inference-prompt-to- utilize-CVEKERNELDIR-whe.patch 0003-Update-to-latest-version-of- clap.patch Cargo.lock Cargo.toml LICENSE README.md analyze_merge_commit.sh io_uring_analysis.txt ksmbd_analysis.txt merge_commit_analysis.txt model prompt src target test_gpio_cleanup.txt test_patch.txt 10 / 256; ``` This confirms that power supply drivers should output temperatures in deci-centigrade (decidegrees). ## Backport Suitability Assessment **1. Bug Fix**: ✅ Yes - This fixes incorrect temperature readings **2. Small and Contained**: ✅ Yes - Only 3 lines changed in one function **3. Clear Side Effects**: ✅ No major side effects - only corrects temperature values **4. Architectural Changes**: ✅ No - Simple unit conversion fix **5. Critical Subsystem**: ✅ Limited impact - only affects optional temperature reporting **6. Stable Tree Mention**: ❌ No explicit mention, but meets criteria **7. Stable Tree Rules**: ✅ Important bugfix with minimal regression risk ## Risk Assessment - **Regression Risk**: Very low - only affects temperature readings when IIO thermal channel is present - **User Impact**: High for affected users - wrong temperature readings could affect thermal management - **Code Complexity**: Minimal - straightforward arithmetic fix ## Historical Context The thermal channel support was added in commit `814755c48f8b` (July 2023), and this scaling bug has been present since then. The fix addresses a fundamental units mismatch that would cause incorrect temperature reporting for any system using the IIO thermal channel feature. This is exactly the type of contained, important bugfix that stable trees are designed for.
drivers/power/supply/max17040_battery.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/drivers/power/supply/max17040_battery.c b/drivers/power/supply/max17040_battery.c index 51310f6e4803b..c1640bc6accd2 100644 --- a/drivers/power/supply/max17040_battery.c +++ b/drivers/power/supply/max17040_battery.c @@ -410,8 +410,9 @@ static int max17040_get_property(struct power_supply *psy, if (!chip->channel_temp) return -ENODATA;
- iio_read_channel_processed_scale(chip->channel_temp, - &val->intval, 10); + iio_read_channel_processed(chip->channel_temp, &val->intval); + val->intval /= 100; /* Convert from milli- to deci-degree */ + break; default: return -EINVAL;