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hwmon: (lm75) Fix setting polarity mask for chips with 16-bit config register

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When probing a 16-bit compatible temperature sensor configured with the
"ti,alert-polarity-active-high" device property, lm75_generic_probe()
writes to a reserved bit instead of the alert polarity bit due to an
incorrect bit shift in the 16-bit polarity mask.
On 16-bit sensors, the polarity bit is physically located at bit 2 of the
MSByte. When accessed via i2c_smbus_read_word_data() or
i2c_smbus_write_word_data(), the SMBus protocol maps the first received
byte (the physical MSByte) to the lower 8 bits of the integer
representation. Consequently, the polarity bit is consistently mapped to
bit 2, identically to 8-bit sensors. However, the
LM75_ALERT_POLARITY_HIGH_16_BIT macro applies an 8-bit left shift,
erroneously targeting bit 10. This causes the driver to silently corrupt a
reserved bit in the configuration register while leaving the active-high
alert polarity unconfigured, breaking the polarity feature.

Use BIT(2) as polarity mask in the configuration register for all chips
to fix the problem.

Reported-by: Sashiko <sashiko-bot@kernel.org>
Fixes: 1be4001d9b ("hwmon: (lm75) Support active-high alert polarity")
Cc: stable@vger.kernel.org
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
This commit is contained in:
Guenter Roeck 2026-10-30 18:59:26 -07:00
parent 4fc79634af
commit 3897309ede
1 changed files with 2 additions and 7 deletions
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9
drivers/hwmon/lm75.c
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@ -123,8 +123,7 @@ struct lm75_data {
static const u8 lm75_sample_set_masks[] = { 0 << 5, 1 << 5, 2 << 5, 3 << 5 };
#define LM75_ALERT_POLARITY_HIGH_8_BIT (BIT(2))
#define LM75_ALERT_POLARITY_HIGH_16_BIT (BIT(2) << 8)
#define LM75_ALERT_POLARITY_HIGH_BIT BIT(2)
#define LM75_SAMPLE_CLEAR_MASK (3 << 5)
/* The structure below stores the configuration values of the supported devices.
@ -770,11 +769,7 @@ static int lm75_generic_probe(struct device *dev, const char *name,
data->orig_conf = status;
/* Enforce polarity active-low (default) or active-high (devicetree) */
if (!data->params->config_reg_16bits)
pol_mask = LM75_ALERT_POLARITY_HIGH_8_BIT;
else
pol_mask = LM75_ALERT_POLARITY_HIGH_16_BIT;
pol_mask = LM75_ALERT_POLARITY_HIGH_BIT;
clr_mask = data->params->clr_mask | pol_mask;
set_mask = data->params->set_mask & ~pol_mask;
if (device_property_read_bool(dev, "ti,alert-polarity-active-high"))