On Mon, 2018-07-02 at 18:04 +0800, Jisheng Zhang wrote:

For Synopsys DesignWare 8250 uart which version >= 4.00a, there's a
valid divisor latch fraction register. The fractional divisor width is
4bits ~ 6bits.

There are several serial IPs that have fractional divider built-in. None
is using any specific hooks. Why do you need in your case, esp. taking
into consideration that we have a custom ->set_termios() callback?

patch1 introduces necessary hooks to 8250 core.
patch2 implement the fractional divisor support for Synopsys DW 8250.

Jisheng Zhang (2):
  serial: 8250: introduce get_divisor() and set_divisor() hook
  serial: 8250_dw: add fractional divisor support

 drivers/tty/serial/8250/8250_core.c |  4 +++
 drivers/tty/serial/8250/8250_dw.c   | 54
+++++++++++++++++++++++++++++
 drivers/tty/serial/8250/8250_port.c |  8 +++++
 include/linux/serial_8250.h         |  7 ++++
 4 files changed, 73 insertions(+)

-- 
Andy Shevchenko [off-list ref]
Intel Finland Oy