Re: [PATCH 1/2] dt-bindings: serial: 8250: add Microchip Core16550

[Conor Dooley <conor@kernel.org>]

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On Mon, Nov 09, 2026 at 01:54:17PM +1100, Kohei Otsuka wrote:
> On Thu, Nov 5, 2026 at 3:20 AM Conor Dooley <conor@kernel.org> wrote:
> >
> > On Tue, Nov 03, 2026 at 11:11:31AM +1100, Kohei Otsuka wrote:
> > > Core16550 is a 16550-compatible UART soft IP core for Microchip FPGAs,
> > > including the fabric of PolarFire SoC. Its registers follow the 16550A,
> > > so ns16550a stays the fallback, but
> >
> > > it raises no interrupt on TEMT,
> > > which the driver has to know about to support RS-485 on it.
> >
> > Doesn't this exclude using the fallback to ns16550a, since it requires
> > specific interrupt handling?
> >
> Everything a plain ns16550a driver does works on
> Core16550 including transmit, receive, FIFOs, modem control and the baud rate
> divisor. The only thing that needs the specific compatible string is
> software RS-485
> (em485), which waits for a TEMT interrupt the core doesn’t raise.
> Without the patch, RS-485 direction control is missing, but the UART
> otherwise works. If you’d rather
> not have the fallback, I can match the compatible in 8250_of directly.

In my opinion, this is enough to invalidate the ns16550a fallback.

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