09864c1cdf
Introduce support for LINFlex driver, based on:
- the version of Freescale LPUART driver after commit b3e3bf2ef2c7 ("Merge
4.0-rc7 into tty-next");
- commit abf1e0a98083 ("tty: serial: fsl_lpuart: lock port on console
write").
In this basic version, the driver can be tested using initramfs and relies
on the clocks and pin muxing set up by U-Boot.
Remarks concerning the earlycon support:
- LinFlexD does not allow character transmissions in the INIT mode (see
section 47.4.2.1 in the reference manual[1]). Therefore, a mutual
exclusion between the first linflex_setup_watermark/linflex_set_termios
executions and linflex_earlycon_putchar was employed and the characters
normally sent to earlycon during initialization are kept in a buffer and
sent afterwards.
- Empirically, character transmission is also forbidden within the last 1-2
ms before entering the INIT mode, so we use an explicit timeout
(PREINIT_DELAY) between linflex_earlycon_putchar and the first call to
linflex_setup_watermark.
- U-Boot currently uses the UART FIFO mode, while this driver makes the
transition to the buffer mode. Therefore, the earlycon putchar function
matches the U-Boot behavior before initializations and the Linux behavior
after.
[1] https://www.nxp.com/webapp/Download?colCode=S32V234RM
Signed-off-by: Stoica Cosmin-Stefan <cosmin.stoica@nxp.com>
Signed-off-by: Adrian.Nitu <adrian.nitu@freescale.com>
Signed-off-by: Larisa Grigore <Larisa.Grigore@nxp.com>
Signed-off-by: Ana Nedelcu <B56683@freescale.com>
Signed-off-by: Mihaela Martinas <Mihaela.Martinas@freescale.com>
Signed-off-by: Matthew Nunez <matthew.nunez@nxp.com>
[stefan-gabriel.mirea@nxp.com: Reduced for upstreaming and implemented
earlycon support]
Signed-off-by: Stefan-Gabriel Mirea <stefan-gabriel.mirea@nxp.com>
Link: https://lore.kernel.org/r/20190809112853.15846-6-stefan-gabriel.mirea@nxp.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.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.