Re: [PATCH 2/3] serial: 8250_dw: configure the Allwinner H616 UART

[Chen-Yu Tsai]

On Sat, Oct 24, 2026 at 10:19 PM Andy Shevchenko
<andriy.shevchenko@xxxxxxxxxxxxxxx> wrote:
>
> On Sat, Oct 24, 2026 at 10:10:33PM +0900, Chen-Yu Tsai wrote:
> > On Sat, Oct 24, 2026 at 12:12 AM James Hilliard
> > <james.hilliard1@xxxxxxxxx> wrote:
> > > On Fri, Oct 23, 2026 at 2:44 AM Andy Shevchenko
> > > <andriy.shevchenko@xxxxxxxxxxxxxxx> wrote:
> > > > On Fri, Oct 23, 2026 at 01:33:50AM -0600, James Hilliard wrote:
>
> ...
>
> > > > >       /* Internal 8250 only */
> > > > >       UART_PORT_AIROHA                = 124,
> > > > >       UART_PORT_AIROHA_HS             = 125,
> > > > > +     UART_PORT_DW_APB_256    = 126,
> > > >
> > > > Why? Besides the poorly chosen name, what prevents us from modifying the
> > > > corresponding parameters at probe time by leaving the one of the existing
> > > > types?
> > >
> > > The new type was primarily a way to reuse the core's FIFO configuration
> > > table, including the RX trigger mapping. H616 uses thresholds of 1, 64,
> > > 128 and 254 bytes, whereas PORT_16550A maps the same FCR bits to 1, 4, 8
> > > and 14 bytes. Overriding only fifosize and tx_loadsz would leave
> > > rx_trig_bytes reporting and selecting the wrong thresholds.
> > >
> > > The core already has get_rxtrig/set_rxtrig callbacks, though. I'll rework
> > > this to retain PORT_16550A, supply the H616 FIFO parameters during setup,
> > > and use those callbacks for the correct trigger mapping.
> >
> > Please consider just taking the FIFO size from the DT. On some chips
> > not every UART has the same size FIFO, so we already need to deal with
> > it.
> >
> > Also, FIFO size is a standard UART DT property, though somehow not included
> > for dw-uart.
>
> FWIW, it supports all standard properties for UART.
> Check what uart_read_port_properties() does.

Ah, that's nice. I hacked up something [1] in the past to get it to
work, but that was probably before you added the helper. I never got
around to splitting up the commits and sending it out.


ChenYu

[1] https://git.kernel.org/pub/scm/linux/kernel/git/wens/linux.git/commit/?id=e7e0741fa04f349ad9f94a4059e32467a30ef5d9