[U-Boot] [PATCH v1 3/4] serial: add an of-platdata driver for "snps, dw-apb-uart"

[Alexey Brodkin <alexey.brodkin@synopsys.com>]

Hi Simon,

[snip]

> >> +config DESIGNWARE_SERIAL
> >> +	bool "DesignWare UART support"
> >> +	depends on DM_SERIAL && SPL_OF_PLATDATA
> >
> > Might be a bit naïve question but why depend on SPL_OF_PLATDATA only?
> > What about CONFIG_OF_EMBED?

Ok I completely forgot that standard ns16550 driver already covers DW APB UART,
see https://elixir.bootlin.com/u-boot/latest/source/drivers/serial/ns16550.c#L456

> > I'd happily switch my ARC boards on this driver and get rid of all
> > CONFIG_SYS_NS16550_xxx nonsense in include/configs/myboardname.h
> 
> I checked include/configs/socfpga_common.h again and by its using
> Kconfig and DM_SERIAL, there are no CONFIG_SYS_NS16550_xxx defines left
> (other than CONFIG_SYS_NS16550_SERIAL, which I will remove).

So it's not that easy apparently :)
At least CONFIG_SYS_NS16550_MEM32 is still used really required
for getting correct accessor used, see implementation of
serial_{in|out}_shift() in drivers/serial/ns16550.c.

If CONFIG_SYS_NS16550_MEM32 is not set then simple readb() is used so
that 8-bit data offset in 32-bit word is lost and we're dead in the water.

That said accessors in ns16550 are begging for significant rework to make
the driver completely OF-driven.

-Alexey