This changes how the SPI message for the triggered buffer is setup in
the TI ADS7950 A/DC driver. By using the SPI_CS_WORD flag, we can read
multiple samples in a single SPI transfer. If the SPI controller
supports DMA transfers, we can see a significant reduction in CPU usage.
For example, on an ARM9 system running at 456MHz reading just 4 channels
at 100Hz: before this change, top shows the CPU usage of the IRQ thread
of this driver to be ~7.7%. After this change, the CPU usage drops to
~3.8%.
The use of big-endian for the raw data was cargo culted from another
driver when this driver was originally written. It used an SPI word size
of 8 bits and big-endian byte ordering to effectively emulate 16 bit
words.
Now, in order to inject a CS toggle between each word, we need to use
the correct word size, otherwise we would get a CS toggle half way
through each word 16-bit. The SPI subsystem uses CPU byte ordering for
multi-byte words. So, the data we get back from the SPI is going to be
CPU endian now no matter what. Converting that to big endian will just
add overhead on little endian systems so we opt to change the raw data
format from big endian to CPU endian.
There is a small risk that this could break some lazy userspace programs
that use the raw data without checking the data format. We can address
this if/when it actually comes up.
Signed-off-by: David Lechner <david@lechnology.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
This modifies the TI ADS7950 A/DC driver to allow the simultaneous use
of both the triggered buffer and reading channels directly (via in-
kernel API or sysfs).
The use case for this is on LEGO MINDSTORMS EV3. Two of the voltage
channels are used in-kernel by a power supply driver, which reads the
values using iio_read_channel_processed(). These channels are only read
at a slow rate (<= 1Hz). However, we want to be able to read 12 other
channels at the same time using the triggered buffer at a high rate (>=
100Hz).
Signed-off-by: David Lechner <david@lechnology.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
This updates the ti-ads7950.c file to use SPDX-License-Identifier
instead of more verbose license text.
Signed-off-by: David Lechner <david@lechnology.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
The equivalent of both of these are now done via macro magic when
the relevant register calls are made. The actual structure
elements will shortly go away.
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Lars-Peter Clausen <lars@metafoo.de>
ACPI enabled platforms do not have a mean of regulators. Instead we use
hard coded voltage value for reference pin. When value is 0 (default) we
fall back to request a regulator.
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
The driver doesn't have a struct of_device_id table but supported devices
are registered via Device Trees. This is working on the assumption that a
SPI device registered via OF will always match a legacy SPI device ID and
that the MODALIAS reported will always be of the form spi:<device>.
There is an ACPI method to enumerate such devices via specific ACPI ID
and use of compatible strings. It will not work for the drivers which
have no OF match ID table present.
Besides this could change in the future so the correct approach is to
have an OF device ID table if the devices are registered via OF.
Tested-by: David Lechner <david@lechnology.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
This changes the reference voltage regulator matching string from "refin"
to "vref". This is to be consistent with other A/DC chips that also use
"vref-supply" in their device tree bindings.
Signed-off-by: David Lechner <david@lechnology.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>
This drops the "ti-" prefix from the module name. It makes the module name
consistent with other iio ti-ads* drivers and it makes the driver work
with device tree (the spi subsystem drops the "ti," prefix when matching
compatible strings from device tree).
Tested working on LEGO MINDSTORMS EV3 with the following device tree node:
adc@3 {
compatible = "ti,ads7957";
reg = <3>;
#io-channel-cells = <1>;
spi-max-frequency = <10000000>;
vref-supply = <&adc_ref>;
};
Signed-off-by: David Lechner <david@lechnology.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>
This adds a new driver for the TI ADS7950 family of ADC chips. These
communicate using SPI and come in 8/10/12-bit and 4/8/12/16 channel
varieties.
Signed-off-by: David Lechner <david@lechnology.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>
David Lechner