[GIT PULL 2/3] ARM: tegra: move fuse code out of arch/arm

[Catalin Marinas]

On Mon, Jul 21, 2014 at 09:06:00AM -0600, Stephen Warren wrote:
> On 07/17/2014 11:33 PM, Olof Johansson wrote:
> > On Thu, Jul 17, 2014 at 7:45 PM, Stephen Warren <swarren at wwwdotorg.org> wrote:
> >> On 07/08/2014 11:47 AM, Olof Johansson wrote:
> >>> On Tue, Jul 8, 2014 at 6:43 AM, Peter De Schrijver
> >>> <pdeschrijver at nvidia.com> wrote:
> >>>> On Mon, Jul 07, 2014 at 02:44:17AM +0200, Olof Johansson wrote:
> >>>>> On Mon, Jun 23, 2014 at 03:23:45PM -0600, Stephen Warren wrote:
> >>>>>> This branch moves code related to the Tegra fuses out of arch/arm and
> >>>>>> into a centralized location which could be shared with ARM64. It also
> >>>>>> adds support for reading the fuse data through sysfs.
> >>>>>
> >>>>> The new/moved misc driver isn't acked by any misc maintainer, so I can't
> >>>>> take this branch.
> >>>>>
> >>>>> I saw no indication from searching the mailing list of that either,
> >>>>> so it wasn't just a missed acked-by.
> >>>>>
> >>>>> I wonder if this code should go under drivers/soc/ instead?
> >>>>
> >>>> It's modelled after sunxi_sid.c which lives in drivers/misc/eeprom/.
> >>>> Originally this driver was also in drivers/misc/eeprom/, but Stephen objected
> >>>> and therefore it was moved to drivers/misc/fuse. I think that's the right
> >>>> place still.
> >>>
> >>> I disagree, I think this belongs under drivers/soc. Especially since
> >>> you're adding dependencies on this misc driver from other parts of the
> >>> kernel / other drivers.
> >>>
> >>> I also don't like seeing init calls form platform code down into
> >>> drivers/misc like you're adding here. Can you please look at doing
> >>> that as a regular init call setup?
> >>
> >> I strongly disagree with using init calls for this kind of thing. There
> >> are ordering dependencies between the initialization code that can only
> >> be sanely managed by explicitly calling functions in a particular order;
> >> there's simply no way to manage this using initcalls. This is exactly
> >> why the hooks in the ARM machine descriptors exist...
> > 
> > Right, but there are non on 64-bit, so you need to solve it for there
> > anyway. And once it's solved there, you might as well keep it common
> > with 32-bit.
> 
> My assertion is that we should just do it directly on 64-bit too.
> There's no reason for arm64 to deviate from what arch/arm does already.

On arm64, I really want to get away from any SoC specific early
initcall. One of the main reason is for things like SCU, interconnects,
system cache configurations (even certain clocks) to be enabled in
firmware before Linux starts (it's an education process but that's a way
for example to prevent people sending patches to enable SoC coherency
because they haven't thought about it before upstreaming).

It would be nice to be able to initialise SoC stuff at device_initcall()
level (and even keep such code as modules in initramfs) but one of the
problems we have is dependency on clocks (and the clock model which
doesn't follow the device/driver model). The of_platform_populate() is
called at arch_initcall_sync (after arch_initcall to still allow some
SoC code, if needed, to run at arch_initcall).

We have a similar issue with arm64 vexpress (well, just on the model)
where vexpress_sysreg_init() is a core_initcall (should be fine as
arch_initcall) as it needs to be done before of_platform_populate().
Pawel on cc should know more of the history here.

I recall there were also some discussions about a SoC driver model which
hangs off the top compatible string in the DT (e.g. "arm,vexpress") and
allow (minimal) code to be run slightly earlier, though still not
earlier than arch_initcall.

-- 
Catalin