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

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

quoted

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

quoted

add device tree bindings document for reboot-mode driver

Signed-off-by: Andy Yan <andy.yan@rock-chips.com>

---

Changes in v3:
- descirbe all reboot mode as properity instead of subnode

Changes in v2: None
Changes in v1: None

 .../bindings/power/reset/reboot-mode.txt           | 26 ++++++++++++++++
 .../bindings/power/reset/syscon-reboot-mode.txt    | 36 ++++++++++++++++++++++
 2 files changed, 62 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/power/reset/reboot-mode.txt
 create mode 100644 Documentation/devicetree/bindings/power/reset/syscon-reboot-mode.txt

diff --git a/Documentation/devicetree/bindings/power/reset/reboot-mode.txt b/Documentation/devicetree/bindings/power/reset/reboot-mode.txt
new file mode 100644
index 0000000..517080f
--- /dev/null
+++ b/Documentation/devicetree/bindings/power/reset/reboot-mode.txt

@@ -0,0 +1,26 @@
+Generic reboot mode core map driver
+
+This driver get reboot mode arguments and call the write
+interface to stores the magic value in special register
+or ram . Then the bootloader can read it and take different
+action according the argument stored.
+
+All mode properties are vendor specific, it is a indication to tell

The values should be vendor specific. The property names should not. We
can allow vendor specific ones, but we need to have a common set.

quoted

+the bootloder what to do when the system reboot, and should be named
+as mode-xxx = <magic> (xxx is mode name).
+
+- mode-normal: Normal reboot mode, system reboot with command "reboot".
+- mode-recovery: Android Recovery mode, it is a mode to format the device or update a new image.
+- mode-fastboot: Android fastboot mode, it's a mode to  re-flash partitions on the device.
+- mode-loader: A bootloader mode, it's a mode used to download image on Rockchip platform,
+            usually used in development.
+- mode-maskrom: It's a mode to download bootloader on Rockchip platform.
+
+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.

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.

quoted

quoted

+             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.

Though I do like the vendor specific prefix here, as it clarifies how
universal the command is (and its easy add standard commands if they
become more established and remap things in the future).

quoted

quoted

+             mode-maskrom = <BOOT_MASKROM>;

I think this should be "mode-rom-download".

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.

I do think the "bootloader" and "recovery" arguments are somewhat
defacto standards, well established on most android devices.

Yes, otherwise I'd be completely against "mode-bootloader" as the 
property.

I think here the concern is rockchip probably has some userspace that
is already using "reboot maskrom" or "reboot loader" for their own
uses. And its a bit of a pain to ask that userspace to be reworked to

Perhaps those are only for development and change would not be so 
painful.

use "reboot rom-download" or "reboot rockchip,rom-download" depending
on how we try to deal with these.  (Granted, non-upstream interfaces
aren't official, so that is their risk somewhat, but we avoid being
smug about that :)

Or vendor specific modes require vendor specific translation in the 
kernel. 

To some extent we need to design what is right and worry about future 
devices rather than cater to past devices. There's always some 
compromise. What would you design ignoring the existing conditions. 
Start there and then figure out how to make it work with current 
designs.

Another part of the issue is there isn't really a way to probe for
reboot cmd capability here. As much as I'd rather not complicate
things, one couldn't easily extend existing userspace to work with
current kernels as well as future kernels, since the reboot with an
invalid command won't fail. The machine still resets. So you can't try
one and fallback to the other.

Well, that's nice. Maybe we should change that? Or we're stuck with 
that ABI?

Maybe there needs to be a sysfs entry with the list of the supported commands?

You can just read the DT. Although, the problem then is what happens 
when we move to the next firmware interface. We see that some with 
devices having userspace dependencies on ATAGS.

Rob