SPCR table parsing

SPCR table parsing

[Jon Masters]

Hi Folks,

We're implementing support for SPCR table parsing shortly[0], since it
will allow to deprecate supplying a "console=" (and eventually, also
"earlycon=") on 64-bit ARM servers, where it's not always the case that
we can assume a 16550 at a specific address. SPCR has been provided on
x86 systems since 2000 but is not (yet) supported by Linux.

If anyone knows of existing efforts on e.g. x86 or IA64, please get in
touch. I expect the initial implementation to require revision 2+ modern
server systems and possibly be limited to ARM initially.

Thanks,

Jon.

[0] This table is now published under a non-restrictive implementation
license and is linked from the UEFI ACPI documents webpage.

Re: SPCR table parsing

[Jon Masters]

On 01/15/2015 10:08 PM, Jon Masters wrote:

> We're implementing support for SPCR table parsing shortly[0], since it
> will allow to deprecate supplying a "console=" (and eventually, also
> "earlycon=") on 64-bit ARM servers, where it's not always the case that
> we can assume a 16550 at a specific address. SPCR has been provided on
> x86 systems since 2000 but is not (yet) supported by Linux.
> 
> If anyone knows of existing efforts on e.g. x86 or IA64, please get in
> touch. I expect the initial implementation to require revision 2+ modern
> server systems and possibly be limited to ARM initially.

Side note: I preemptively had this added to the SBBR so it's already
required on ARM servers, and have confirmed the reference systems out
there have valid tables for us to use ahead of time.

Jon.

Re: SPCR table parsing

[Mark Rutland]

On Fri, Jan 16, 2015 at 03:08:37AM +0000, Jon Masters wrote:
> Hi Folks,
> 
> We're implementing support for SPCR table parsing shortly[0], since it
> will allow to deprecate supplying a "console=" (and eventually, also
> "earlycon=") on 64-bit ARM servers, where it's not always the case that
> we can assume a 16550 at a specific address. SPCR has been provided on
> x86 systems since 2000 but is not (yet) supported by Linux.

For anyone using DT rather than ACPI, the same can be achieved in
mainline with /chosen/stdout-path as of:

7914a7c5651a5161 "of: support passing console options with stdout-path"

Documented in:

2a9d832cc9aae21e "of: Add bindings for chosen node, stdout-path"

e.g.

uart: serial@f00 {
	reg = <0xf00 0x200>;
	compatible = "vendor,some-serial-device";
};

chosen {
	stdout-path = "/serial@f00:115200n8";
};

This will be used for both the console and earlycon. Please make use of
this where possible.

Thanks,
Mark.