mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
synced 2026-05-10 06:49:29 -04:00
62df72a0ab
spi_mem_calc_op_duration() is deriving the duration of a specific op, by multiplying the number of cycles with the time a cycle will last. This time was measured in nanoseconds, which means at high frequencies the delta between two frequencies might not be properly catch due to roundings. For instance, the Winbond driver has a changing number of dummy cycles depending on the speed, adding +8 dummy cycles when running at 166MHz compared to 162MHz. Both frequencies would lead to using a 6ns delay per cycle for the op duration computation, whereas in practice there is a small difference which actually offsets the number of extra dummy cycles on a normal page read. Augmenting the precision of the calculation by using picoseconds prevents selecting a lower frequency if we can do slightly better with another frequency involving more cycles. As a result, the above situation leads to comparing cycles of 6024 and 6172 picoseconds which leads to picking the most efficient variant. Reviewed-by: Mark Brown <broonie@kernel.org> Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.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 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.