[PATCH 10/10] drivers: PL011: add support for the ARM SBSA generic UART

[Dave Martin]

On Tue, Feb 17, 2015 at 10:55:35AM -0500, Philip Elcan wrote:
> On 01/16/2015 12:23 PM, Andre Przywara wrote:
> > The ARM Server Base System Architecture[1] document describes a
> > generic UART which is a subset of the PL011 UART.
> > It lacks DMA support, baud rate control and modem status line
> > control, among other things.
> > The idea is to move the UART initialization and setup into the
> > firmware (which does this job today already) and let the kernel just
> > use the UART for sending and receiving characters.
> > We use the recent refactoring the build a new struct uart_ops
> > variable which points to some new functions avoiding access to the
> > missing registers. We reuse as much existing PL011 code as possible.
> >
> > In contrast to the PL011 the SBSA UART does not define any AMBA or
> > PrimeCell relations, so we go a pretty generic probe function
> > which only uses platform device functions.
> > A DT binding is provided, but other systems can easily attach to it,
> > too (hint, hint!).
> >
> > Signed-off-by: Andre Przywara <andre.przywara at arm.com>
> > ---
>
> <snip>
>
> Andre,
>
> I'm a little late to address this patchset, but the SBSA defines all
> the Generic UART registers 32-bit wide. However, the amba-pl011 driver
> uses 16-bit accessors. How will you be handling that? Can the ARM PL011
> hardware handle 32-bit access?

Interesting question.  The PL011 TRM [1] specifies only a 16-bit-wide
APB bus interface, but does not say that 32-bit accesses won't work.

I suspect that 32-bit accesses will work on all or most PL011s -- if
that looks too risky or we can't find enough test platforms to be sure
of this, then we could maybe abstract the register access size as a
quirk.

Andre may already have an answer on this.

Cheers
---Dave

[1] ARM DDI 0183G, http://infocenter.arm.com/ -> CoreLink controllers
and peripherals

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