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

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Date:	Fri, 2 Jan 2015 16:47:51 +0000
From:	Catalin Marinas <catalin.marinas@....com>
To:	Hanjun Guo <hanjun.guo@...aro.org>
Cc:	Graeme Gregory <gg@...mlogic.co.uk>,
	"ashwinc@...eaurora.org" <ashwinc@...eaurora.org>,
	"rjw@...ysocki.net" <rjw@...ysocki.net>,
	Mark Rutland <Mark.Rutland@....com>,
	"olof@...om.net" <olof@...om.net>,
	"grant.likely@...aro.org" <grant.likely@...aro.org>,
	Will Deacon <Will.Deacon@....com>,
	"linaro-acpi@...ts.linaro.org" <linaro-acpi@...ts.linaro.org>,
	Liviu Dudau <Liviu.Dudau@....com>,
	"lv.zheng@...el.com" <lv.zheng@...el.com>,
	"robh@...nel.org" <robh@...nel.org>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
	"al.stone@...aro.org" <al.stone@...aro.org>,
	"daniel.lezcano@...aro.org" <daniel.lezcano@...aro.org>,
	"robert.moore@...el.com" <robert.moore@...el.com>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	Charles Garcia-Tobin <Charles.Garcia-Tobin@....com>,
	"rric@...nel.org" <rric@...nel.org>,
	"jason@...edaemon.net" <jason@...edaemon.net>,
	"arnd@...db.de" <arnd@...db.de>,
	Marc Zyngier <Marc.Zyngier@....com>,
	"jcm@...hat.com" <jcm@...hat.com>,
	"broonie@...nel.org" <broonie@...nel.org>,
	"bhelgaas@...gle.com." <linux-arm-kernel@...ts.infradead.org>,
	"graeme.gregory@...aro.org" <graeme.gregory@...aro.org>,
	"Kangkang.Shen@...wei.com" <Kangkang.Shen@...wei.com>,
	"rdunlap@...radead.org" <rdunlap@...radead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Sudeep Holla <Sudeep.Holla@....com>
Subject: Re: [PATCH v5 18/18] Documentation: ACPI for ARM64

On 2 Jan 2015, at 09:28, Hanjun Guo <hanjun.guo@...aro.org> wrote:
>>> On 2015年01月02日 04:04, Graeme Gregory wrote:
>>>> On Wed, Dec 31, 2014 at 04:34:46PM +0800, Hanjun Guo wrote:
>>>> On 2014年12月31日 04:13, ashwinc@...eaurora.org wrote:
>>>> Hi Hanjun,
>>>> 
>>>> Overall the document looks good to us. Some minor clarifications below.
>>>> 
>>>>> ---------- Forwarded message ----------
>>>>> From: Graeme Gregory <graeme.gregory@...aro.org>
>>>>> 
>>>>> Add documentation for the guidelines of how to use ACPI
>>>>> on ARM64.
>>>>> 
>>>>> Signed-off-by: Graeme Gregory <graeme.gregory@...aro.org>
>>>>> Signed-off-by: Al Stone <al.stone@...aro.org>
>>>>> Signed-off-by: Hanjun Guo <hanjun.guo@...aro.org>
>>>>> ---
>>>>> Documentation/arm64/arm-acpi.txt |  323
>>>>> ++++++++++++++++++++++++++++++++++++++
>>>>> 1 file changed, 323 insertions(+)
>>>>> create mode 100644 Documentation/arm64/arm-acpi.txt
>>>> 
>>>> [..]
>>>> 
>>>>> +Relationship with Device Tree
>>>>> +-----------------------------
>>>> 
>>>> [..]
>>>> 
>>>>> +When booting using ACPI tables, the /chosen node in DT will still be
>>>>> parsed
>>>>> +to extract the kernel command line and initrd path.  No other section of
>>>>> the
>>>>> +DT will be used.
>>>> 
>>>> Is this still true?
>>> 
>>> No, we can booting the ACPI system in EFI stub without dtb. Catalin
>>> also pointed out this issue, I will remove this paragraph.
>> 
>> The paragraph is still correct, the /chosen node is always present even
>> if nothing else is.
> 
> Sorry for the confusing, I mean no dtb needed for the command line if
> ACPI tables are available.
> 
> efi will create a empty dtb if no dtb found, and add the cmd line into
> the new created dtb, I'm just wondering, can we remove the limitation
> for passing the cmd line in /chosen node in the future?

My point is that on an ACPI based system, we don't really care how EFI_STUB passes
the command line to the rest of the kernel. Since UEFI doesn't need to know about
such detail and since ACPI is only supported with EFI_STUB, we don't need to mention
the chosen node in this document. 

At some point we may even change the way EFI_STUB passes the command line to the 
kernel but this is still irrelevant to ACPI. 

Catalin

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