On Thu, Feb 04, 2016 at 09:03:44PM -0800, John Stultz wrote:

On Thu, Feb 4, 2016 at 8:35 PM, Rob Herring [off-list ref] wrote:

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On Thu, Feb 04, 2016 at 03:46:15PM -0800, John Stultz wrote:

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On Thu, Feb 4, 2016 at 3:08 PM, Rob Herring [off-list ref] wrote:

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On Tue, Feb 02, 2016 at 05:59:11PM +0800, Andy Yan wrote:

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+Example:
+     reboot-mode {
+             mode-normal = <BOOT_NORMAL>;
+             mode-recovery = <BOOT_RECOVERY>;
+             mode-fastboot = <BOOT_FASTBOOT>;

I tend to agree with John on calling this mode-bootloader.

OTOH, fastboot is more specific about what the mode is. The name in DT
and the userspace name don't necessarily have to be the same.

Wait. This is a bit confusing. The utility of adding a property name
and using that name be the reboot command parsed for made sense
(compared to earlier versions which had command strings) as it made
the dts more terse.   But it sounds here like you're suggesting we
should have some logic in the driver that translates "reboot fastboot"
to mode-bootloader or vice versa.

I said early on the DT names and kernel-userspace names should not
necessarily be linked. They can be, but we shouldn't require that.

Sigh. Ok. It seemed it was due to earlier comments (maybe from others,
but I thought it was you), that we moved from specifying a command
string, to using the label. But if you think the label name and the
commands shouldn't be linked, it seems like we should re-introduce
that. No?

Unless your thinking we need some sort of static in-kernel mapping of
commands to label names? But that just seems painfully indirect for
little gain ("Its obvious! For that mode, you use this term here, and
that different term over there!").

Tying it to a Linux ABI makes the binding Linux specific. I don't have a 
problem that the strings happen to be the same, but we should have some 
understanding that they may not be and allow for that.

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My concern with mode-bootloader is what if you can boot into multiple
bootloader modes. Say USB mass storage is one option. "bootloader" is
not real specific.

True. But as I think we agreed below, "bootloader" and "recovery" are
basically defacto standards, and I think it would be a bad idea to try
to declare all the existing android tooling and docs wrong just
because the command is vague, technically.

Okay, as long as they are clearly documented what they mean.

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+             mode-loader = <BOOT_LOADER>;

This one needs a better name. Maybe it should be 'rockchip,mode-loader'
as it is vendor specific. Either way, loader is vague. Perhaps
rockchip,mode-bl-download?

Hrm. So how what reboot command do you expect to trigger that?

Whatever your OS has defined to map to that.

We could just decide the kernel will strip <vendor> and 'mode-' and
match commands against what remains.

That part sounds sane, although I do think having vendor prefixes are
reasonable for actual commands as well.

Well, you could still have "rockchip,mode-rockchip-bl-download"... 

We can bikeshed that when get there.

The other way random custom modes could be done is just allow the raw 
value to be passed from userspace converting the string to a number. 
Then we have no abstraction rather than half way abstracting it.

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I think one of the difficult things here is that there's no real
standards for all bios/bootloader modes. So they are somewhat
firmware/bootloader/device specific, and thus we need something that
is flexible enough to allow lots of different modes to be easily
specified.  That said, this does expose a userspace interface (though
one could argue kernel ABI doesn't cross reboots :) so we should try
to have some consistency so the same userspace can work on various
devices.

There is: UEFI. Boot mode efivars are standard. But then they are pretty
much PC oriented though. It is more which device to boot off of, but
there is network boot or boot to bios setup.

Well, there's a partial standard there.  I'm told for android on x86,
there is no UEFI standard way to communicate rebooting to fastboot or
recovery. Every device does its own device specific driver.

So much for standards. However, while these specific modes have not been 
standardized, there is a set of standard modes and these could have been 
added to the existing mechanism. So there at least exists some model to 
draw inspiration from.

Rob