Re: [PATCH v3 02/17] ARM64 / ACPI: Get RSDP and ACPI boot-time tables

Mark Rutland
2014-09-09T17:15:46Z

On Tue, Sep 09, 2014 at 05:41:51PM +0100, Jon Masters wrote:
> On 09/09/2014 12:26 PM, Catalin Marinas wrote:
> > On Mon, Sep 01, 2014 at 03:57:40PM +0100, Hanjun Guo wrote:
> >> diff --git a/arch/arm64/include/asm/acenv.h b/arch/arm64/include/asm/acenv.h
> >> new file mode 100644
> >> index 0000000..3899ee6
> >> --- /dev/null
> >> +++ b/arch/arm64/include/asm/acenv.h
> >> @@ -0,0 +1,18 @@
> >> +/*
> >> + * ARM64 specific ACPICA environments and implementation
> >> + *
> >> + * Copyright (C) 2014, Linaro Ltd.
> >> + * Author: Hanjun Guo <hanjun.guo@linaro.org>
> >> + * Author: Graeme Gregory <graeme.gregory@linaro.org>
> >> + *
> >> + * This program is free software; you can redistribute it and/or modify
> >> + * it under the terms of the GNU General Public License version 2 as
> >> + * published by the Free Software Foundation.
> >> + */
> >> +
> >> +#ifndef _ASM_ACENV_H
> >> +#define _ASM_ACENV_H
> >> +
> >> +#define ACPI_FLUSH_CPU_CACHE() WARN_ONCE(1, "Not currently supported on ARM64")
> >
> > Does this mean that it will be supported at some point? Looking at the
> > places where this function is called, I don't really see how this would
> > ever work on ARM. Which means that we add such macro just to be able to
> > compile code that would never be used on arm64. I would rather see the
> > relevant ACPI files only compiled on x86/IA-64 rather than arm64.
>
> That specific cache behavior is a part of e.g. ACPI C3 state support
> (e.g. ACPI5.1 8.1.4 Processor Power State C3).

Per table 5-35, if neither WBINVD or WBINVD_FLUSH are set in the FADT,
we don't get S1, S2, or S3 states either.

> As you note, it's not going to work on 64-bit ARM as it does on x86,
> but it's optional to implement C3 and early 64-bit ARM systems should
> not report Wbindv flags in the FADT anyway.

Unless the arm cache architecture changes, I wouldn't expect any 64-bit
ARM system to set either of the WBINVD flags.

> They can also set FADT.P_LVL3_LAT > 1000, which has the effect of
> disabling C3 support, while also allowing for use of _CST objects to
> define more flexible C-States later on.

It sounds like we should be sanity checking these in the arm64 ACPI code
for the moment. I don't want us to discover that current platforms
report the wrong thing only when new platforms come out that might
actually report things correctly.

Mark.