On Mon, 2022-05-23 at 19:11 +0200, Sven Anderson wrote:
> Hi all,
>
> Am Do., 18. März 2021 um 23:08 Uhr schrieb Benjamin Herrenschmidt
> <b...@kernel.crashing.org>:
> > This adds the ability for the driver to access UARTs via MMIO instead
> > of PIO selectively at runtime, and exposes a new function to add an
> > MMIO port.
>
> I had a couple of sleepless nights trying to find out why this didn't
> work for my MMIO UART (Intel Cannon Lake PCH Intel C246), so I
> thought I would share my findings with others in a similar situation.
> (See below.)
Thanks ! I'm overdue to re-submit those patches :-)
> > diff --git a/grub-core/term/ns8250.c b/grub-core/term/ns8250.c
> > index 39809d042..183e14b3b 100644
> > --- a/grub-core/term/ns8250.c
> > +++ b/grub-core/term/ns8250.c
> > @@ -44,6 +44,24 @@ static int dead_ports = 0;
> > #define DEFAULT_BASE_CLOCK 115200
> > #endif
> >
> > +static inline unsigned char
> > +ns8250_reg_read (struct grub_serial_port *port, grub_addr_t reg)
> > +{
> > + asm volatile("" : : : "memory");
> > + if (port->mmio)
> > + return *((volatile unsigned char *)(port->mmio_base + reg));
> > + return grub_inb (port->port + reg);
> > +}
> > +
> > +static inline void
> > +ns8250_reg_write (struct grub_serial_port *port, unsigned char value,
> > grub_addr_t reg)
> > +{
> > + asm volatile("" : : : "memory");
> > + if (port->mmio)
> > + *((volatile char *)(port->mmio_base + reg)) = value;
> > + else
> > + grub_outb (value, port->port + reg);
> > +}
>
> This code assumes that the registers are only 8 bit wide. Apparently
> for my chipset they are 32 bits wide, so it only (finally) worked
> when I rewrote this code to address and write full grub_uint32_t
> values, like this:
Ah yes, there are all sort of "interesting" variations of MMIO UART
layout and my patch didn't add >8 bits as I didn't need it. The
information is available via SPCR though, so when I finally get a
chance to respin this series, I'll try to add something and ask you to
test if you don't mind ?
PS. I'm quite swamped this week, in absence of news from me in a couple
of weeks, feel free to poke for a heads up !
Cheers,
Ben.
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