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The I2C-bus to the XPower AXP288 is shared between the Linux kernel and the SoCs P-Unit. The P-Unit has a semaphore which the kernel must "lock" before it may use the bus and while the kernel holds the semaphore the CPU and GPU power-states must not be changed otherwise the system will freeze. This is a complex process, which is quite expensive. This is all done by iosf_mbi_block_punit_i2c_access(). To ensure that no unguarded I2C-bus accesses happen, iosf_mbi_block_punit_i2c_access() gets called by the I2C-bus-driver for every I2C transfer. Because this is so expensive it is allowed to call iosf_mbi_block_punit_i2c_access() in a nested fashion, so that higher-level code which does multiple I2C-transfers can call it once for a group of transfers, turning the calls done by the I2C-bus-driver into no-ops. Add iosf_mbi_block_punit_i2c_access() calls around groups of register accesses, so that the P-Unit semaphore only needs to be taken once for each group of register accesses. Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com> Signed-off-by: Hans de Goede <hdegoede@redhat.com> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.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.