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The available_scan_mask is an array of bitmaps representing the channels which can be simultaneously enabled by the driver. In many cases, the hardware can offer more channels than what the user is interested in obtaining. In such cases, it may be preferred that only a subset of channels are enabled, and the driver reads only a subset of the channels from the hardware. Some devices can't support all channel combinations. For example, the BM1390 pressure sensor must always read the pressure data in order to acknowledge the watermark IRQ, while reading temperature can be omitted. So, the available scan masks would be 'pressure and temperature' and 'pressure only'. When IIO searches for the scan mask it asks the driver to use, it will pick the first suitable one from the 'available_scan_mask' array. Hence, ordering the masks in the array makes a difference. We should 'prefer' reading just the pressure from the hardware (as it is a cheaper operation than reading both pressure and temperature) over reading both pressure and temperature. Hence, we should set the 'only pressure' as the first scan mask in available_scan_mask array. If we set the 'pressure and temperature' as first in the array, then the 'only temperature' will never get used as 'pressure and temperature' can always serve the user's needs. Add (minimal) kerneldoc to the 'available_scan_mask' to hint the user that the ordering of masks matters. Signed-off-by: Matti Vaittinen <mazziesaccount@gmail.com> Link: https://lore.kernel.org/r/4e43bf0186df5c8a56b470318b4827605f9cad6c.1695727471.git.mazziesaccount@gmail.com Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
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.
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.