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c449ad7425The code currently responsible for the SPI communication speed setting up is a bit messy. Most likely for some historical reason the bus frequency is saved in the peripheral chip private data. It's pointless now since the custom communication speed is a SPI-transfer-specific thing and only if there is no SPI transfer data specified (like during the SPI memory operations) it can be taken from the SPI device structure. But even in the later case there is no point in having the clock divider and the SPI bus frequency saved in the chip data, because the controller can be used for both SPI-transfer-based and SPI-transfer-less communications. From software point of view keeping the current clock divider in an SPI-device specific storage may give a small performance gain (to avoid sometimes a round-up division), but in comparison to the total SPI transfer time it just doesn't worth saving a few CPU cycles in comparison to the total SPI transfer time while having the harder to read code. The only optimization, which could worth preserving in the code is to avoid unnecessary DW SPI controller registers update if it's possible. So to speak let's simplify the SPI communication speed update procedure by removing the clock-related fields from the peripheral chip data and update the DW SPI clock divider only if it's really changed. The later change is reached by keeping the effective SPI bus speed in the internal DW SPI private data. Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru> Link: https://lore.kernel.org/r/20201007235511.4935-6-Sergey.Semin@baikalelectronics.ru Signed-off-by: Mark Brown <broonie@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 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.