Re: [PATCH v5 18/18] Documentation: ACPI for ARM64

From: Hanjun Guo <hanjun.guo@linaro.org>
To: Catalin Marinas <catalin.marinas@arm.com>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>,
	Mark Rutland <Mark.Rutland@arm.com>,
	Olof Johansson <olof@lixom.net>,
	"grant.likely@linaro.org" <grant.likely@linaro.org>,
	Will Deacon <Will.Deacon@arm.com>,
	"graeme.gregory@linaro.org" <graeme.gregory@linaro.org>,
	Arnd Bergmann <arnd@arndb.de>,
	Sudeep Holla <Sudeep.Holla@arm.com>,
	"jcm@redhat.com" <jcm@redhat.com>,
	Jason Cooper <jason@lakedaemon.net>,
	Marc Zyngier <Marc.Zyngier@arm.com>,
	Bjorn Helgaas <bhelgaas@google.com>,
	Daniel Lezcano <daniel.lezcano@linaro.org>,
	Mark Brown <broonie@kernel.org>, Rob Herring <robh@kernel.org>,
	Robert Richter <rric@kernel.org>, Lv Zheng <lv.zheng@intel.com>,
	Robert Moore <robert.moore@intel.com>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@arm.com>,
	Liviu Dudau <Liviu.Dudau@arm.com>,
	Randy Dunlap <rdunlap@infradead.org>,
	Charles Garcia-Tobin <Charles.Garcia-Tobin@arm.com>,
	"Kangkang.Shen@huawei.com" <Kangkang.Shen@huawei.com>,
	"linux-acpi@vger.kernel.org" <linux-acpi@vger.kernel.org>,
	"linux-arm-kernel@lists.infradead.org" 
	<linux-arm-kernel@lists.infradead.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linaro-acpi@lists.linaro.org" <linaro-acpi@lists.linaro.org>,
	Al Stone <al.stone@linaro.org>
Subject: Re: [PATCH v5 18/18] Documentation: ACPI for ARM64
Date: Sun, 04 Jan 2015 17:39:24 +0800	[thread overview]
Message-ID: <54A90A4C.60908@linaro.org> (raw)
In-Reply-To: <20141224171815.GD13399@e104818-lin.cambridge.arm.com>

On 2014年12月25日 01:18, Catalin Marinas wrote:
[...]
>
> In addition to the above and _DSD requirements/banning, I would also add
> some clear statements around:
>
> _OSC: only global/published capabilities are allowed. For
> device-specific _OSC we need a process or maybe we can ban them entirely
> and rely on _DSD once we clarify the process.
>
> _OSI: firmware must not check for certain _OSI strings. Here I'm not
> sure what we would have to do for ARM Linux. Reporting "Windows" does
> not make any sense but not reporting anything can, as Matthew Garrett
> pointed out, can be interpreted by firmware as "Linux". In addition to
> any statements in this document, I suggest you patch
> drivers/acpi/acpica/utosi.c accordingly, maybe report "Linux" for ARM
> and print a kernel warning so that we notice earlier.
>
> ACPI_OS_NAME: this is globally defined as "Microsoft Windows NT". It
> doesn't make much sense in the ARM context. Could we change it to
> "Linux" when CONFIG_ARM64?

We will work on this both on ASWG and linux ACPI driver side, as Dong
and Charles pointed out, _OSI things can be solved in ACPI spec, when
that is done, we can modify the kernel driver to fix the problems above.

>
> Compatibility with older kernels: ACPI firmware must work, even though
> not fully optimal, with the earliest kernel version implementing the
> targeted ACPI spec. There may be a need for new drivers but otherwise
> adding things like CPU power management should not break older kernel
> versions. In addition, the ACPI firmware must also work with the latest
> kernel version.

It should be, and I think that's why we need ACPI (or DT) here :)

Thanks
Hanjun