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As per RZ/V2M hardware manual(Rev.1.30 Jun, 2022), UART IP has a restriction as mentioned below. 40.6.1 Point for Caution when Changing the Register Settings: When changing the settings of the following registers, a PRESETn master reset or FIFO reset + SW reset (FCR[2],FCR[1], HCR0[7]) must be input to re-initialize them. Target Registers: FCR, LCR, MCR, DLL, DLM, HCR0. Add serial8250_em_reg_update() and serial8250_em_serial_out_helper() to handle this restriction. serial8250_em_serial_out_helper() is identical to previous serial8250_em_serial_out() except that UART_FCR macro is removed from serial8250_em_serial_out_helper() as it is now handled by serial8250_ em_serial_out(). DLL/DLM register can be updated only by setting LCR[7]. So the updation of LCR[7] will perform reset for DLL/DLM register changes. EMMA mobile has the same register set as RZ/V2M and this patch is tested on EMEV2 board. So, there is no harm in applying the same restriction here as well as the HW manual for EMMA mobile is not updated for a long time. Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com> Link: https://lore.kernel.org/r/20230227114152.22265-8-biju.das.jz@bp.renesas.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.