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Several camera sensor drivers access the "clock-frequency" property directly to retrieve the external clock rate, or modify the clock rate of the external clock programmatically. Both behaviours are valid on a subset of ACPI platforms, but are considered deprecated on OF platforms, and do not support ACPI platforms that implement MIPI DisCo for Imaging. Implementing them manually in drivers is deprecated, as that can encourage cargo-cult and lead to differences in behaviour between drivers. Instead, drivers should use the devm_v4l2_sensor_clk_get() helper. This driver supports ACPI and OF platforms. The "clocks" property has always been specified as mandatory in the DT bindings and the "clock-frequency" property has always been optional. The driver retrieves the clock and its rate if present, and falls back to retrieving the rate from the "clock-frequency" property otherwise. If the rate does not match one of the supported rates, the driver fails probing. If a clock is available and the "clock-frequency" property is set, the driver sets the rate of the clock to the value of the property. It does however use the rate initially retrieved from the clock for further calculations, which is a bug if the rates don't match, and would prevent the sensor from functioning properly. We can therefore assume that this case never occurs, and that the driver behaves correctly for ACPI, and for OF platforms that comply with the documented DT bindings. Switch to using the devm_v4l2_sensor_clk_get() helper. This does not change the behaviour on ACPI platforms that specify a clock-frequency property and don't provide a clock. On ACPI platforms that provide a clock, the clock rate will be set to the value of the clock-frequency property. This should not change the behaviour either as this driver expects the clock to be set to that rate, and wouldn't operate correctly otherwise. Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com> Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com> Reviewed-by: Mehdi Djait <mehdi.djait@linux.intel.com> Signed-off-by: Hans Verkuil <hverkuil+cisco@kernel.org> |
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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 reStructuredText 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.