On Mon, 2018-07-02 at 13:18 +0300, Andy Shevchenko wrote:

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

quoted

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?

Okay, I see that in 8250 we have hooks embedded into 8250_port.c which
is not the best solution.

For example it prevents better splitting Exar code.
So, we would need these hooks, but better to integrate them in the same
way like it's done for the rest of 8250 ones, i.e.
- rename existing to have a "do" word
- create new functions which would be a replacement that choose between
"do" variant and custom one
- not sure if we need to export "do" variants (at least for now)

quoted

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