Re: [RFC][PATCH] misc: Introduce reboot_reason driver

On Thu, Dec 10, 2015 at 12:56 PM, John Stultz [off-list ref] wrote:

On Thu, Dec 10, 2015 at 6:52 AM, Arnd Bergmann [off-list ref] wrote:

quoted

On Wednesday 09 December 2015 17:19:52 John Stultz wrote:

quoted

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