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Caching register values can be very expensive for PMBus chips. Some modern chips may have 10 or more pages, with several sensors supported per page. For example, MAX16601 creates more than 90 sysfs attributes. Register caching for such chips is time consuming, especially if only a few attributes are read on a regular basis. For MAX16601, it was observed that it can take up to two seconds to read all attributes on a slow I2C bus. In this situation, register caching results in the opposite of its intention: It increases the number of I2C operations, in some cases substantially, and it results in large latency when trying to access individual sensor data. Drop all register caching to solve the problem. Since it is no longer necessary, drop status register mapping as part of the change, and specify status registers directly. Cc: Alex Qiu <xqiu@google.com> Signed-off-by: Guenter Roeck <linux@roeck-us.net> Reviewed-by: Alex Qiu <xqiu@google.com> Tested-by: Alex Qiu <xqiu@google.com> Link: https://lore.kernel.org/r/20200904163314.259087-1-linux@roeck-us.net Signed-off-by: Guenter Roeck <linux@roeck-us.net>
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.