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hwmon: (ads7871) Propagate SPI errors in voltage_show 

The voltage_show() function previously ignored negative error codes
returned by the underlying SPI read/write functions. Because negative
numbers have their most significant bits set in two's complement, a
failed SPI read returning -EIO (-5) would incorrectly evaluate to true
when masked with MUX_CNV_BM (0x80).

This would cause the driver to enter the polling loop even when the SPI bus
failed, eventually returning a misleading -ETIMEDOUT error to userspace
instead of the actual hardware error. Furthermore, the return values of
the initial SPI write and the final 16-bit SPI read were completely
ignored.

Add proper error checking after every SPI operation to ensure hardware
failures are immediately propagated back to userspace.

Suggested-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Tabrez Ahmed <tabreztalks@gmail.com>
Link: https://lore.kernel.org/r/20260308124714.84715-1-tabreztalks@gmail.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
This commit is contained in:
Tabrez Ahmed 2026-03-08 18:17:14 +05:30 committed by Guenter Roeck
parent 0a42986b65
commit 487a9ab28f
1 changed files with 10 additions and 2 deletions
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12
drivers/hwmon/ads7871.c
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@ -104,10 +104,14 @@ static ssize_t voltage_show(struct device *dev, struct device_attribute *da,
*/
/*MUX_M3_BM forces single ended*/
/*This is also where the gain of the PGA would be set*/
ads7871_write_reg8(spi, REG_GAIN_MUX,
(MUX_CNV_BM | MUX_M3_BM | channel));
ret = ads7871_write_reg8(spi, REG_GAIN_MUX,
(MUX_CNV_BM | MUX_M3_BM | channel));
if (ret < 0)
return ret;
ret = ads7871_read_reg8(spi, REG_GAIN_MUX);
if (ret < 0)
return ret;
mux_cnv = ((ret & MUX_CNV_BM) >> MUX_CNV_BV);
/*
* on 400MHz arm9 platform the conversion
@ -116,12 +120,16 @@ static ssize_t voltage_show(struct device *dev, struct device_attribute *da,
while ((i < 2) && mux_cnv) {
i++;
ret = ads7871_read_reg8(spi, REG_GAIN_MUX);
if (ret < 0)
return ret;
mux_cnv = ((ret & MUX_CNV_BM) >> MUX_CNV_BV);
msleep_interruptible(1);
}
if (mux_cnv == 0) {
val = ads7871_read_reg16(spi, REG_LS_BYTE);
if (val < 0)
return val;
/*result in volts*10000 = (val/8192)*2.5*10000*/
val = ((val >> 2) * 25000) / 8192;
return sysfs_emit(buf, "%d\n", val);