linux-kernel - Re: [PATCH v8 08/21] dt / chosen: Add linux,uefi-stub-generated-dtb property

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Message-ID: <54D5884A.6050009@linaro.org>
Date:	Sat, 07 Feb 2015 11:36:42 +0800
From:	Hanjun Guo <hanjun.guo@...aro.org>
To:	G Gregory <graeme.gregory@...aro.org>,
	Mark Rutland <mark.rutland@....com>,
	Leif Lindholm <leif.lindholm@...aro.org>
CC:	Catalin Marinas <Catalin.Marinas@....com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Olof Johansson <olof@...om.net>, Arnd Bergmann <arnd@...db.de>,
	"grant.likely@...aro.org" <grant.likely@...aro.org>,
	Will Deacon <Will.Deacon@....com>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
	Sudeep Holla <Sudeep.Holla@....com>,
	"jcm@...hat.com" <jcm@...hat.com>,
	Jason Cooper <jason@...edaemon.net>,
	Marc Zyngier <Marc.Zyngier@....com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Mark Brown <broonie@...nel.org>, Rob Herring <robh@...nel.org>,
	Robert Richter <rric@...nel.org>,
	Randy Dunlap <rdunlap@...radead.org>,
	Charles Garcia-Tobin <Charles.Garcia-Tobin@....com>,
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	Timur Tabi <timur@...eaurora.org>,
	Ashwin Chaugule <ashwinc@...eaurora.org>,
	"suravee.suthikulpanit@....com" <suravee.suthikulpanit@....com>,
	Mark Langsdorf <mlangsdo@...hat.com>,
	"wangyijing@...wei.com" <wangyijing@...wei.com>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linaro-acpi@...ts.linaro.org" <linaro-acpi@...ts.linaro.org>,
	Jonathan Corbet <corbet@....net>,
	Matt Fleming <matt.fleming@...el.com>
Subject: Re: [PATCH v8 08/21] dt / chosen: Add linux,uefi-stub-generated-dtb
 property

On 2015年02月06日 18:34, G Gregory wrote:
[...]
>>>>>   --------------------------------------------------------------------------------
>>>>>   linux,uefi-stub-kern-ver  | string | Copy of linux_banner from build.
>>>>>   --------------------------------------------------------------------------------
>>>>> +linux,uefi-stub-generated-dtb  | bool | Indication for no DTB provided by
>>>>> +                        |      | firmware.
>>>>> +--------------------------------------------------------------------------------
>>>>
>>>> Apologies for the late bikeshedding, but the discussion on this topic
>>>> previsously was lively enough that I thought I'd let it die down a bit
>>>> before seeing if I had anything to add.
>>>>
>>>> That, and I just realised something:
>>>> One alternative to this added DT entry is that we could treat the
>>>> absence of a registered UEFI configuration table as the indication
>>>> that no HW description was provided from firmware, since the stub does
>>>> not call InstallConfigurationTable() on the DT it generates. This does
>>>> move the ability to detect to after efi_init(), but this should be
>>>> fine for ACPI-purposes.
>>>>
>>> That would not work as expected in the kexec/Xen use case though as they
>>> may genuinely boot with DT from an ACPI host without UEFI.
>>
>> I'm a little concerned by this case. How do we intend to pass stuff from
>> Xen to the kernel in this case? When we initially discussed the stub
>> prior to merging, we weren't quite sure if ACPI without UEFI was
>> entirely safe.
>>
>> The linux,uefi-stub-kern-ver property was originally intended as a
>> sanity-check feature to ensure nothing (including Xen) masqueraded as
>> the stub, but for some reason the actual sanity check was never
>> implemented.
>>
>>>> If that is deemed undesirable, I would still prefer Catalin's
>>>> suggested name ("linux,bare-dtb"), which describes the state rather
>>>> than the route we took to get there.
>>>>
>>> I agree.
>>
>> I guess this would be ok, though it would be nice to know which agent
>> generated the DTB.
>>
>
> The most obvious scheme then is
>
> linux,bare-dtb = "uefi-stub";
>
> otherwise we generate a new binding for every component in the boot path.

Leif, Mark, any comments on this?

Thanks
Hanjun
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