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hwmon: (ads7871) Use DMA-safe buffer for SPI writes

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The driver currently passes a stack-allocated buffer to spi_write(),
which is incompatible with DMA on systems with CONFIG_VMAP_STACK
enabled.

Move the transfer buffer into the driver's private data structure
to ensure it is DMA-safe. Since this shared buffer now requires
serialization, this change depends on the previous commit which
migrated the driver to the hwmon 'with_info' API.

While moving the logic, also:
- Corrected the sign extension for 14-bit data by casting to s16.
- Scaled the output to millivolts (2500mV full scale
) to comply with the hwmon ABI.

Signed-off-by: Tabrez Ahmed <tabreztalks@gmail.com>
Link: https://lore.kernel.org/r/20260502020844.110038-4-tabreztalks@gmail.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
This commit is contained in:
Tabrez Ahmed 2026-05-02 07:38:44 +05:30 committed by Guenter Roeck
parent a2b0986398
commit b46e1a0bff
1 changed files with 21 additions and 14 deletions
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35
drivers/hwmon/ads7871.c
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@ -63,6 +63,7 @@
struct ads7871_data {
struct spi_device *spi;
u8 tx_buf[2] ____cacheline_aligned;
};
static umode_t ads7871_is_visible(const void *data,
@ -95,11 +96,12 @@ static int ads7871_read_reg16(struct spi_device *spi, int reg)
return le16_to_cpu((__force __le16)ret);
}
static int ads7871_write_reg8(struct spi_device *spi, int reg, u8 val)
static int ads7871_write_reg8(struct ads7871_data *pdata, int reg, u8 val)
{
u8 tmp[2] = {reg, val};
pdata->tx_buf[0] = reg;
pdata->tx_buf[1] = val;
return spi_write(spi, tmp, sizeof(tmp));
return spi_write(pdata->spi, pdata->tx_buf, 2);
}
static int ads7871_read(struct device *dev, enum hwmon_sensor_types type,
@ -118,7 +120,7 @@ static int ads7871_read(struct device *dev, enum hwmon_sensor_types type,
*/
/*MUX_M3_BM forces single ended*/
/*This is also where the gain of the PGA would be set*/
ret = ads7871_write_reg8(spi, REG_GAIN_MUX,
ret = ads7871_write_reg8(pdata, REG_GAIN_MUX,
(MUX_CNV_BM | MUX_M3_BM | channel));
if (ret < 0)
return ret;
@ -126,6 +128,7 @@ static int ads7871_read(struct device *dev, enum hwmon_sensor_types type,
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
@ -145,8 +148,11 @@ static int ads7871_read(struct device *dev, enum hwmon_sensor_types type,
if (raw_val < 0)
return raw_val;
/*result in volts*10000 = (val/8192)*2.5*10000*/
*val = ((raw_val >> 2) * 25000) / 8192;
/*
* Use (s16) to ensure the sign bit is preserved during the shift.
* Report millivolts (2.5V = 2500mV).
*/
*val = ((s16)raw_val >> 2) * 2500 / 8192;
return 0;
}
@ -183,11 +189,17 @@ static int ads7871_probe(struct spi_device *spi)
spi->bits_per_word = 8;
spi_setup(spi);
ads7871_write_reg8(spi, REG_SER_CONTROL, 0);
ads7871_write_reg8(spi, REG_AD_CONTROL, 0);
pdata = devm_kzalloc(dev, sizeof(*pdata), GFP_KERNEL);
if (!pdata)
return -ENOMEM;
pdata->spi = spi;
ads7871_write_reg8(pdata, REG_SER_CONTROL, 0);
ads7871_write_reg8(pdata, REG_AD_CONTROL, 0);
val = (OSC_OSCR_BM | OSC_OSCE_BM | OSC_REFE_BM | OSC_BUFE_BM);
ads7871_write_reg8(spi, REG_OSC_CONTROL, val);
ads7871_write_reg8(pdata, REG_OSC_CONTROL, val);
ret = ads7871_read_reg8(spi, REG_OSC_CONTROL);
dev_dbg(dev, "REG_OSC_CONTROL write:%x, read:%x\n", val, ret);
@ -198,11 +210,6 @@ static int ads7871_probe(struct spi_device *spi)
if (val != ret)
return -ENODEV;
pdata = devm_kzalloc(dev, sizeof(struct ads7871_data), GFP_KERNEL);
if (!pdata)
return -ENOMEM;
pdata->spi = spi;
hwmon_dev = devm_hwmon_device_register_with_info(dev, spi->modalias,
pdata,
&ads7871_chip_info,