[PATCH] serial: 8250_platform: Enable generic 16550A platform devices

[Andy Shevchenko]

On Tue, Sep 17, 2024 at 06:10:25AM -0700, Palmer Dabbelt wrote:
> On Mon, 29 Jul 2024 22:12:18 PDT (-0700), Sunil V L wrote:
> > Currently, 8250_platform driver is used only for devices with fixed
> > serial ports (plat_serial8250_port). Extend this driver for any generic
> > 16550A platform devices which can be probed using standard hardware
> > discovery mechanisms like ACPI.
> >
> > This is required in particular for RISC-V which has non-PNP generic
> > 16550A compatible UART that needs to be enumerated as ACPI platform
> > device.

> It seems a bit awkward that we need something RISC-V specific here.  I 
> guess the idea is that we don't want to depend on PNP because we'd end 
> up with a bunch of PCI dependencies as well?  That seems like kind of an 
> odd way to do things, but I'm frequently suprised by ACPI stuff so

We have the same for HSUART on Intel (see 8250_dw.c). The ACPI devices use
different approach than PNP. PNP has the exact requirements for compatibility
with the legacy UARTs (to some extend). It puts some limitations. I believe
having specifics for RISC-V is fine. But I haven't checked the real IP used
in the SoC. If it's one that we have the existing driver for (like again
mentioned 8250_dw.c), then it should be added there.

TL;DR: so, what is the IP is in hardware for UART? Custom?

-- 
With Best Regards,
Andy Shevchenko