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| author | Luiz Sampaio <sampaio.ime@gmail.com> | 2021-05-19 19:30:46 -0300 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2021-05-21 14:51:33 +0200 |
| commit | c999fbbdcf778c2ea77f59e26d7448a1ab8fa8a2 (patch) | |
| tree | 5b34a7edafc482b89659100a27383abb748edfe5 /drivers | |
| parent | fd6ec5d79507f99639c94f107e8a98550c9e1cf6 (diff) | |
| download | lwn-c999fbbdcf778c2ea77f59e26d7448a1ab8fa8a2.tar.gz lwn-c999fbbdcf778c2ea77f59e26d7448a1ab8fa8a2.zip | |
w1: ds2438: support for writing to offset register
Added a sysfs entry to support writing to the offset register on page1.
This register is used to calibrate the chip canceling offset errors in the
current ADC. This means that, over time, reading the IAD register will not
return the correct current measurement, it will have an offset. Writing to
the offset register if the two's complement of the current register while
passing zero current to the load will calibrate the measurements. This
change was tested on real hardware and it was able to calibrate the chip
correctly.
Signed-off-by: Luiz Sampaio <sampaio.ime@gmail.com>
Link: https://lore.kernel.org/r/20210519223046.13798-7-sampaio.ime@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'drivers')
| -rw-r--r-- | drivers/w1/slaves/w1_ds2438.c | 49 |
1 files changed, 49 insertions, 0 deletions
diff --git a/drivers/w1/slaves/w1_ds2438.c b/drivers/w1/slaves/w1_ds2438.c index 42080ae779f0..ca64f99c8f3d 100644 --- a/drivers/w1/slaves/w1_ds2438.c +++ b/drivers/w1/slaves/w1_ds2438.c @@ -193,6 +193,34 @@ static int w1_ds2438_change_config_bit(struct w1_slave *sl, u8 mask, u8 value) return -1; } +static int w1_ds2438_change_offset_register(struct w1_slave *sl, u8 *value) +{ + unsigned int retries = W1_DS2438_RETRIES; + u8 w1_buf[9]; + u8 w1_page1_buf[DS2438_PAGE_SIZE + 1 /*for CRC*/]; + + if (w1_ds2438_get_page(sl, 1, w1_page1_buf) == 0) { + memcpy(&w1_buf[2], w1_page1_buf, DS2438_PAGE_SIZE - 1); /* last register reserved */ + w1_buf[7] = value[0]; /* change only offset register */ + w1_buf[8] = value[1]; + while (retries--) { + if (w1_reset_select_slave(sl)) + continue; + w1_buf[0] = W1_DS2438_WRITE_SCRATCH; + w1_buf[1] = 0x01; /* write to page 1 */ + w1_write_block(sl->master, w1_buf, 9); + + if (w1_reset_select_slave(sl)) + continue; + w1_buf[0] = W1_DS2438_COPY_SCRATCH; + w1_buf[1] = 0x01; + w1_write_block(sl->master, w1_buf, 2); + return 0; + } + } + return -1; +} + static int w1_ds2438_get_voltage(struct w1_slave *sl, int adc_input, uint16_t *voltage) { @@ -364,6 +392,25 @@ static ssize_t page1_read(struct file *filp, struct kobject *kobj, return ret; } +static ssize_t offset_write(struct file *filp, struct kobject *kobj, + struct bin_attribute *bin_attr, char *buf, + loff_t off, size_t count) +{ + struct w1_slave *sl = kobj_to_w1_slave(kobj); + int ret; + + mutex_lock(&sl->master->bus_mutex); + + if (w1_ds2438_change_offset_register(sl, buf) == 0) + ret = count; + else + ret = -EIO; + + mutex_unlock(&sl->master->bus_mutex); + + return ret; +} + static ssize_t temperature_read(struct file *filp, struct kobject *kobj, struct bin_attribute *bin_attr, char *buf, loff_t off, size_t count) @@ -430,6 +477,7 @@ static ssize_t vdd_read(struct file *filp, struct kobject *kobj, static BIN_ATTR_RW(iad, 0); static BIN_ATTR_RO(page0, DS2438_PAGE_SIZE); static BIN_ATTR_RO(page1, DS2438_PAGE_SIZE); +static BIN_ATTR_WO(offset, 2); static BIN_ATTR_RO(temperature, 0/* real length varies */); static BIN_ATTR_RO(vad, 0/* real length varies */); static BIN_ATTR_RO(vdd, 0/* real length varies */); @@ -438,6 +486,7 @@ static struct bin_attribute *w1_ds2438_bin_attrs[] = { &bin_attr_iad, &bin_attr_page0, &bin_attr_page1, + &bin_attr_offset, &bin_attr_temperature, &bin_attr_vad, &bin_attr_vdd, |