linux-kernel - Re: [RFC][PATCH] misc: Introduce reboot

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Date:	Thu, 10 Dec 2015 14:24:11 -0600
From:	Rob Herring <robh+dt@...nel.org>
To:	John Stultz <john.stultz@...aro.org>
Cc:	Arnd Bergmann <arnd@...db.de>,
	Bjorn Andersson <bjorn.andersson@...ymobile.com>,
	lkml <linux-kernel@...r.kernel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Vinay Simha BN <simhavcs@...il.com>,
	Haojian Zhuang <haojian.zhuang@...aro.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Android Kernel Team <kernel-team@...roid.com>,
	Andy Gross <agross@...eaurora.org>,
	"linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>
Subject: Re: [RFC][PATCH] misc: Introduce reboot_reason driver

On Thu, Dec 10, 2015 at 12:56 PM, John Stultz <john.stultz@...aro.org> wrote:
> On Thu, Dec 10, 2015 at 6:52 AM, Arnd Bergmann <arnd@...db.de> wrote:
>> On Wednesday 09 December 2015 17:19:52 John Stultz wrote:
>>>
>>> If the concern is that since DT is basically ABI, one might not want
>>> to have such a wide interface that specifies all the different
>>> reasons, I can understand that. Though I'm really not sure how else we
>>> would be able to specify the device supported the reboot reason logic
>>> w/o having something in the DT (since some device may use the same soc
>>> w/  the same reboot logic may use a different bootloader which doesn't
>>> support the reason methods). At that point if we don't describe the
>>> method clearly, it ends up being something closer to just a quirks
>>> list which we'd have to map internally to behavior, which doesn't seem
>>> great.
>>>
>>> Should we run into hardware that the proposed driver doesn't handle,
>>> we can introduce a new driver for those specific semantics, but this
>>> way we can share at least most of the logic, no?
>>
>> I think we need a layered approach, with some high-level code to
>> store the boot reason, but then support firmware specific backends
>> to that. If we just need a phandle for an SRAM partition and an offset
>> within it, that can be done by the high-level driver, but not
>> any of the more sophisticated communication methods.
>
> Hrm. This feels to me like over-design, though. We already have the
> restart notifiers to hook into, which provide the command string. So
> its just a matter of parsing the string and writing the appropriate
> magic in the appropriate way (to memory, registers, efi, whatever).
> The amount of code we'd be dealing with to have a front end and 3-4
> back-ends, vs having 3-4 separate drivers seems like it would almost
> be the same. So why try to make a more complicated infrastructure?

The fact that we are using notifiers for reset reason and triggering
is probably some indication that some infrastructure is needed. But I
don't think you need to do that here as long as it is all kernel
internals. We'll make the 2nd guy do it. ;)

Rob
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