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Channel 6 of the SAR ADC can be switched between two inputs: SAR_ADC_CH6 input (an actual pad on the SoC) and the signal from the temperature sensor inside the SoC. To get usable results from the temperature sensor we need to read the corresponding calibration data from the eFuse and pass it to the SAR ADC registers. If the temperature sensor is not calibrated (the eFuse data contains a bit for this) then the driver will only register the iio_chan_spec's for voltage measurements. This only enables the temperature sensor for the Meson8 SoC. Meson8b and Meson8m2 SoCs can be supported in the future as well but we first need a way to pass the fifth TSC (temperature sensor coefficient) bit to the HHI register area (apart from that the infrastructure as already implemented for Meson8 can be used). On the 64-bit SoCs (GXBB, GXL and GXM) the temperature sensor inside SAR ADC is firmware-controlled (by BL30, we can simply use the SCPI hwmon driver to get the chip temperature). To keep the devicetree interface backwards compatible we simply skip the temperature sensor initialization if no eFuse nvmem cell is passed via devicetree. The public documentation for the SAR ADC IP block does not explain how to use the registers to read the temperature. The logic from this patch is based on reading and understanding Amlogic's GPL kernel sources. Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com> Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com> |
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.