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This Cadence QSPI IP has a 4-bit clock divisor field for baud rate division. For example: 0b0000 = /2 0b0001 = /4 0b0010 = /6 ... 0b1111 = /32 The maximum divisor is 32 (when div = CQSPI_REG_CONFIG_BAUD_MASK). If we assume a reference clock of 500MHz and we set our spi-max-frequency to something low, such as 10 MHz. The calculated bit field for the divisor ends up being: DIV_ROUND_UP(500000000/(2*10000000))-1 = 25 25 is 0b11001... which truncates to a divisor field of 0b1001 (or /20). This is higher than our anticipated max-frequency of 10MHz (500MHz/20 = 25 MHz). Instead, let's make sure we're always using the maximum divisor (/32) in this case and give the user a warning about the rate adjustment. Signed-off-by: Nathan Barrett-Morrison <nathan.morrison@timesys.com> Link: https://lore.kernel.org/r/20221128164147.158441-1-nathan.morrison@timesys.com Signed-off-by: Mark Brown <broonie@kernel.org>
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.