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Subject[PATCH 4.19 186/276] iio: ad_sigma_delta: Properly handle SPI bus locking vs CS assertion
Date
[ Upstream commit df1d80aee963480c5c2938c64ec0ac3e4a0df2e0 ]

For devices from the SigmaDelta family we need to keep CS low when doing a
conversion, since the device will use the MISO line as a interrupt to
indicate that the conversion is complete.

This is why the driver locks the SPI bus and when the SPI bus is locked
keeps as long as a conversion is going on. The current implementation gets
one small detail wrong though. CS is only de-asserted after the SPI bus is
unlocked. This means it is possible for a different SPI device on the same
bus to send a message which would be wrongfully be addressed to the
SigmaDelta device as well. Make sure that the last SPI transfer that is
done while holding the SPI bus lock de-asserts the CS signal.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Alexandru Ardelean <Alexandru.Ardelean@analog.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/iio/adc/ad_sigma_delta.c | 16 +++++++++++-----
include/linux/iio/adc/ad_sigma_delta.h | 1 +
2 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/drivers/iio/adc/ad_sigma_delta.c b/drivers/iio/adc/ad_sigma_delta.c
index ae2a5097f4493..25af4c76b57fe 100644
--- a/drivers/iio/adc/ad_sigma_delta.c
+++ b/drivers/iio/adc/ad_sigma_delta.c
@@ -62,7 +62,7 @@ int ad_sd_write_reg(struct ad_sigma_delta *sigma_delta, unsigned int reg,
struct spi_transfer t = {
.tx_buf = data,
.len = size + 1,
- .cs_change = sigma_delta->bus_locked,
+ .cs_change = sigma_delta->keep_cs_asserted,
};
struct spi_message m;
int ret;
@@ -218,6 +218,7 @@ static int ad_sd_calibrate(struct ad_sigma_delta *sigma_delta,

spi_bus_lock(sigma_delta->spi->master);
sigma_delta->bus_locked = true;
+ sigma_delta->keep_cs_asserted = true;
reinit_completion(&sigma_delta->completion);

ret = ad_sigma_delta_set_mode(sigma_delta, mode);
@@ -235,9 +236,10 @@ static int ad_sd_calibrate(struct ad_sigma_delta *sigma_delta,
ret = 0;
}
out:
+ sigma_delta->keep_cs_asserted = false;
+ ad_sigma_delta_set_mode(sigma_delta, AD_SD_MODE_IDLE);
sigma_delta->bus_locked = false;
spi_bus_unlock(sigma_delta->spi->master);
- ad_sigma_delta_set_mode(sigma_delta, AD_SD_MODE_IDLE);

return ret;
}
@@ -289,6 +291,7 @@ int ad_sigma_delta_single_conversion(struct iio_dev *indio_dev,

spi_bus_lock(sigma_delta->spi->master);
sigma_delta->bus_locked = true;
+ sigma_delta->keep_cs_asserted = true;
reinit_completion(&sigma_delta->completion);

ad_sigma_delta_set_mode(sigma_delta, AD_SD_MODE_SINGLE);
@@ -298,9 +301,6 @@ int ad_sigma_delta_single_conversion(struct iio_dev *indio_dev,
ret = wait_for_completion_interruptible_timeout(
&sigma_delta->completion, HZ);

- sigma_delta->bus_locked = false;
- spi_bus_unlock(sigma_delta->spi->master);
-
if (ret == 0)
ret = -EIO;
if (ret < 0)
@@ -316,7 +316,10 @@ int ad_sigma_delta_single_conversion(struct iio_dev *indio_dev,
sigma_delta->irq_dis = true;
}

+ sigma_delta->keep_cs_asserted = false;
ad_sigma_delta_set_mode(sigma_delta, AD_SD_MODE_IDLE);
+ sigma_delta->bus_locked = false;
+ spi_bus_unlock(sigma_delta->spi->master);
mutex_unlock(&indio_dev->mlock);

if (ret)
@@ -353,6 +356,8 @@ static int ad_sd_buffer_postenable(struct iio_dev *indio_dev)

spi_bus_lock(sigma_delta->spi->master);
sigma_delta->bus_locked = true;
+ sigma_delta->keep_cs_asserted = true;
+
ret = ad_sigma_delta_set_mode(sigma_delta, AD_SD_MODE_CONTINUOUS);
if (ret)
goto err_unlock;
@@ -381,6 +386,7 @@ static int ad_sd_buffer_postdisable(struct iio_dev *indio_dev)
sigma_delta->irq_dis = true;
}

+ sigma_delta->keep_cs_asserted = false;
ad_sigma_delta_set_mode(sigma_delta, AD_SD_MODE_IDLE);

sigma_delta->bus_locked = false;
diff --git a/include/linux/iio/adc/ad_sigma_delta.h b/include/linux/iio/adc/ad_sigma_delta.h
index 730ead1a46df6..57c122ae54523 100644
--- a/include/linux/iio/adc/ad_sigma_delta.h
+++ b/include/linux/iio/adc/ad_sigma_delta.h
@@ -66,6 +66,7 @@ struct ad_sigma_delta {
bool irq_dis;

bool bus_locked;
+ bool keep_cs_asserted;

uint8_t comm;

--
2.20.1


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