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Message-ID: <20240914123611.3fdb1fbf@jic23-huawei>
Date: Sat, 14 Sep 2024 12:36:11 +0100
From: Jonathan Cameron <jic23@...nel.org>
To: Vasileios Amoiridis <vassilisamir@...il.com>
Cc: dan.carpenter@...aro.org, linux-iio@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: iio: pressure: bmp280: Use char instead of s32 for data buffer
On Fri, 23 Aug 2024 19:20:17 +0200
Vasileios Amoiridis <vassilisamir@...il.com> wrote:
> As it was reported and discussed here [1], storing the sensor data in an
> endian aware s32 buffer is not optimal. Advertising the timestamp as an
> addition of 2 s32 variables which is also implied is again not the best
> practice. For that reason, change the s32 sensor_data buffer to a char
> buffer with an extra value for the timestamp (as it is common practice).
>
> [1]: https://lore.kernel.org/linux-iio/73d13cc0-afb9-4306-b498-5d821728c3ba@stanley.mountain/
>
> Signed-off-by: Vasileios Amoiridis <vassilisamir@...il.com>
Hi.
Thanks for poking. Looks like I'd accidentally marked this one handled
without actually doing so :(
> ---
> drivers/iio/pressure/bmp280-core.c | 43 +++++++++++++++++-------------
> drivers/iio/pressure/bmp280.h | 5 +++-
> 2 files changed, 28 insertions(+), 20 deletions(-)
>
> diff --git a/drivers/iio/pressure/bmp280-core.c b/drivers/iio/pressure/bmp280-core.c
> index 3deaa57bb3f5..71e481c2f30d 100644
> --- a/drivers/iio/pressure/bmp280-core.c
> +++ b/drivers/iio/pressure/bmp280-core.c
> @@ -1035,7 +1035,8 @@ static irqreturn_t bmp280_trigger_handler(int irq, void *p)
> goto out;
> }
>
> - data->sensor_data[1] = bmp280_compensate_temp(data, adc_temp);
> + ret = bmp280_compensate_temp(data, adc_temp);
> + memcpy(&data->buffer.buf[4], &ret, 4);
The 4's in here are magic indexes. Probably use sizeof(s32) in both cases.
Maybe for the first one make the fact it's after an s32 explicit with
&data->buffer.buf[1 * sizeof(s32)]
Of carry an offset through the code that you update when you fill in part of
the buffer. That is probably cleaner.
int offset = 0;
stuff
offset += sizeof(s32);
mempcy(&data->bufer.buf[offset], &ret, 4);
if offset is used for a later entry then add the new element.
>
> /* Pressure calculations */
> adc_press = FIELD_GET(BMP280_MEAS_TRIM_MASK, get_unaligned_be24(&data->buf[0]));
> @@ -1045,10 +1046,10 @@ static irqreturn_t bmp280_trigger_handler(int irq, void *p)
> }
>
> t_fine = bmp280_calc_t_fine(data, adc_temp);
> + ret = bmp280_compensate_press(data, adc_press, t_fine);
> + memcpy(&data->buffer.buf[0], &ret, 4);
>
> - data->sensor_data[0] = bmp280_compensate_press(data, adc_press, t_fine);
> -
> - iio_push_to_buffers_with_timestamp(indio_dev, &data->sensor_data,
> + iio_push_to_buffers_with_timestamp(indio_dev, &data->buffer,
> iio_get_time_ns(indio_dev));
>
> out:
> @@ -1148,7 +1149,8 @@ static irqreturn_t bme280_trigger_handler(int irq, void *p)
> goto out;
> }
>
> - data->sensor_data[1] = bmp280_compensate_temp(data, adc_temp);
> + ret = bmp280_compensate_temp(data, adc_temp);
> + memcpy(&data->buffer.buf[4], &ret, 4);
>
> /* Pressure calculations */
> adc_press = FIELD_GET(BMP280_MEAS_TRIM_MASK, get_unaligned_be24(&data->buf[0]));
> @@ -1158,8 +1160,8 @@ static irqreturn_t bme280_trigger_handler(int irq, void *p)
> }
>
> t_fine = bmp280_calc_t_fine(data, adc_temp);
> -
> - data->sensor_data[0] = bmp280_compensate_press(data, adc_press, t_fine);
> + ret = bmp280_compensate_press(data, adc_press, t_fine);
> + memcpy(&data->buffer.buf[0], &ret, 4);
>
> /* Humidity calculations */
> adc_humidity = get_unaligned_be16(&data->buf[6]);
> @@ -1168,9 +1170,11 @@ static irqreturn_t bme280_trigger_handler(int irq, void *p)
> dev_err(data->dev, "reading humidity skipped\n");
> goto out;
> }
> - data->sensor_data[2] = bme280_compensate_humidity(data, adc_humidity, t_fine);
>
> - iio_push_to_buffers_with_timestamp(indio_dev, &data->sensor_data,
> + ret = bme280_compensate_humidity(data, adc_humidity, t_fine);
> + memcpy(&data->buffer.buf[8], &ret, 4);
as above, but here it is I guess after 2 other elements, so
2 * sizeof(s32)
> +
> + iio_push_to_buffers_with_timestamp(indio_dev, &data->buffer,
> iio_get_time_ns(indio_dev));
>
> out:
> @@ -1628,7 +1632,8 @@ static irqreturn_t bmp380_trigger_handler(int irq, void *p)
> goto out;
> }
>
> - data->sensor_data[1] = bmp380_compensate_temp(data, adc_temp);
> + ret = bmp380_compensate_temp(data, adc_temp);
> + memcpy(&data->buffer.buf[4], &ret, 4);
>
> /* Pressure calculations */
> adc_press = get_unaligned_le24(&data->buf[0]);
> @@ -1638,10 +1643,10 @@ static irqreturn_t bmp380_trigger_handler(int irq, void *p)
> }
>
> t_fine = bmp380_calc_t_fine(data, adc_temp);
> + ret = bmp380_compensate_press(data, adc_press, t_fine);
> + memcpy(&data->buffer.buf[0], &ret, 4);
>
> - data->sensor_data[0] = bmp380_compensate_press(data, adc_press, t_fine);
> -
> - iio_push_to_buffers_with_timestamp(indio_dev, &data->sensor_data,
> + iio_push_to_buffers_with_timestamp(indio_dev, &data->buffer,
> iio_get_time_ns(indio_dev));
>
> out:
> @@ -2203,12 +2208,12 @@ static irqreturn_t bmp580_trigger_handler(int irq, void *p)
> }
>
> /* Temperature calculations */
> - memcpy(&data->sensor_data[1], &data->buf[0], 3);
> + memcpy(&data->buffer.buf[4], &data->buf[0], 3);
>
> /* Pressure calculations */
> - memcpy(&data->sensor_data[0], &data->buf[3], 3);
> + memcpy(&data->buffer.buf[0], &data->buf[3], 3);
> - iio_push_to_buffers_with_timestamp(indio_dev, &data->sensor_data,
> + iio_push_to_buffers_with_timestamp(indio_dev, &data->buffer,
> iio_get_time_ns(indio_dev));
>
> out:
> @@ -2522,15 +2527,15 @@ static irqreturn_t bmp180_trigger_handler(int irq, void *p)
> if (ret)
> goto out;
>
> - data->sensor_data[1] = chan_value;
> + memcpy(&data->buffer.buf[4], &chan_value, 4);
>
> ret = bmp180_read_press(data, &chan_value);
> if (ret)
> goto out;
>
> - data->sensor_data[0] = chan_value;
> + memcpy(&data->buffer.buf[0], &chan_value, 4);
>
> - iio_push_to_buffers_with_timestamp(indio_dev, &data->sensor_data,
> + iio_push_to_buffers_with_timestamp(indio_dev, &data->buffer,
> iio_get_time_ns(indio_dev));
>
> out:
> diff --git a/drivers/iio/pressure/bmp280.h b/drivers/iio/pressure/bmp280.h
> index ccacc67c1473..a853b6d5bdfa 100644
> --- a/drivers/iio/pressure/bmp280.h
> +++ b/drivers/iio/pressure/bmp280.h
> @@ -411,7 +411,10 @@ struct bmp280_data {
> * Data to push to userspace triggered buffer. Up to 3 channels and
> * s64 timestamp, aligned.
> */
> - s32 sensor_data[6] __aligned(8);
> + struct {
> + u8 buf[12];
> + s64 ts __aligned(8);
We have a new aligned_s64 that is cleaner for these cases. It's only
in my togreg branch currently though so you'll need to base on that
to use it.
Jonathan
> + } buffer;
>
> /*
> * DMA (thus cache coherency maintenance) may require the
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