On 22.5.2017 20:26, Alan Cox wrote:

quoted

We have in soc vendor tree similar patch but the reason is different.

    tty: serial: Added a CONFIG_SERIAL_XILINX_NR_UARTS option.

    This patch Adds CONFIG_SERIAL_XILINX_NR_UARTS option to allow
    the user to provide the Max number of uart ports information.
    If multiple cards (or) PL UARTS are present, the default limit
    of 2 ports should be increased.

I haven't checked all drivers but in our case we have added this as
quick fix for scenarios where you use serial aliases where alias is
pointed to serial2 or more.
In cdns_uart_init() cdns_uart_uart_driver is passed which contains .nr
which is required to be passed.

What's the best driver to look at dynamic allocation?

So there are quite a few that dynamically allocate the objects as they
are enumerated (eg max3100), but have a maximum set that is just pointers
(so for the max number of ports cheaper than the dynamic code)

yep hardcoded max 4 where in probe first free space is found and used
(range 0-3) but still max3100s statically allocated.
Shouldn't be this also dynamically allocated?

The other question is why is it a CONFIG_ option. I'm assuming these
platforms are all ARM and in that case you could just pass the value in
the device tree, or hard code a safe maximum number of pointers to a
value which is the worst case and then install them as they are
enumerated.

I am not quite sure how exactly you want to do this via DT.

Also what do you think is a safe maximum number? This is fpga - hundreds
of pins which can do just uart.

There are lots of options better than breaking the "one kernel many
platforms" model.

Another options is also module parameter and dynamically allocated array
in cdns_uart_init.

Thanks,
Michal