[U-Boot] [PATCH v3 00/13] ARMv7: add PSCI support to u-boot

[Marc Zyngier]

On Thu, Apr 17 2014 at  9:34:24 am BST, Albert ARIBAUD <albert.u.boot at aribaud.net> wrote:
> Hi Marc,
>
> On Wed, 16 Apr 2014 17:09:07 +0100, Marc Zyngier <marc.zyngier at arm.com>
> wrote:
>
>> On 16/04/14 15:45, Albert ARIBAUD wrote:
>> > Hi Marc,
>> > 
>> > On Sat, 15 Feb 2014 13:36:24 +0000, Marc Zyngier
>> > <marc.zyngier-5wv7dgnIgG8 at public.gmane.org> wrote:
>> > 
>> >> PSCI is an ARM standard that provides a generic interface that
>> >> supervisory software can use to manage power in the following
>> >> situations:
>> >> - Core idle management
>> >> - CPU hotplug
>> >> - big.LITTLE migration models
>> >> - System shutdown and reset
>> >>
>> >> It basically allows the kernel to offload these tasks to the firmware,
>> >> and rely on common kernel side code.
>> >>
>> >> More importantly, it gives a way to ensure that CPUs enter the kernel
>> >> at the appropriate exception level (ie HYP mode, to allow the use of
>> >> the virtualization extensions), even across events like CPUs being
>> >> powered off/on or suspended.
>> >>
>> >> The main idea here is to turn some of the existing u-boot code into a
>> >> separate section that can live in secure RAM (or a reserved page of
>> >> memory), containing a secure monitor that will implement the PSCI
>> >> operations. This code will still be alive when u-boot is long gone,
>> >> hence the need for a piece of memory that will not be touched by the
>> >> OS.
>> >>
>> >> This patch series contains 4 parts:
>> >> - the first four patches are just bug fixes
>> >> - the next two refactor the HYP/non-secure code to allow relocation
>> >>   in secure memory
>> >> - the next four contain the generic PSCI code and DT infrastructure
>> >> - the last three implement the CPU_ON method of the Allwinner A20 (aka sun7i).
>> >>
>> >> I realize the A20 u-boot code is not upstream yet (BTW is anyone
>> >> actively working on that?), but hopefully that should give a good idea
>> >> of how things are structured so far. The patches are against the
>> >> mainline u-boot tree as of today, merged with the sunxi u-boot tree
>> >> of the day and the first 10 patches will directly apply to mainline
>> >> u-boot.
>> >>
>> >> As for using this code, it goes like this:
>> >> sun7i# ext2load mmc 0:1 0x40008000 zImage ; ext2load mmc 0:1 0x60000000 sun7i-a20-cubietruck.dtb
>> >> 2270120 bytes read in 117 ms (18.5 MiB/s)
>> >> 9138 bytes read in 3 ms (2.9 MiB/s)
>> >> sun7i# fdt addr 0x60000000 ; fdt resize ; fdt set ethernet0 mac-address "[5a fe b0 07 b0 07]"
>> >> sun7i# setenv bootargs console=ttyS0,115200 earlyprintk ip=dhcp root=/dev/nfs nfsroot=/backup/a20_root,tcp
>> >> sun7i# bootz 0x40008000 - 0x60000000
>> >>
>> >> The kernel now boots in HYP mode, finds its secondary CPU without any
>> >> SMP code present in the kernel, and runs KVM out of the box.
>> >> I've been told the Xen/ARM guys managed to do the same fairly easily.
>> >>
>> >> This code has also been tested on a VExpress TC2, running KVM with all
>> >> 5 CPUs, in order to make sure there was no obvious regression.
>> >>
>> >> I'm wildly cross-posting this patch series, including to lists I'm not
>> >> subscribed to. Please keep me on Cc for any comment you may have.
>> >>
>> >> The code is also available at:
>> >> git://git.kernel.org/pub/scm/linux/kernel/git/maz/u-boot.git wip/psci
>> >>
>> >> Cheers,
>> >>
>> >>         M.
>> > 
>> > Marc, I'm unclear what you want to do with this series. You mention
>> > that its first 10 patches will apply to U-Boot, but I am not sure
>> > whether you are just indicating that it is possible to apply them or
>> > asking for these 10 patches to go in U-Boot mainline.  Or is it
>> > something else yet?
>> 
>> Well, I rarely write code just for the sake of forking a critical
>> project ;-)
>> 
>> So let's be 100% explicit: Yes, I'm hereby asking for these patches to
>> be merged. They offer a service that is required by the Linux kernel as
>> well as Xen. They are in active use on the Allwinner sun7i platform as
>> well as Versatile Express (though the later doesn't have a PSCI
>> implementation).
>> 
>> Now, given that two months have gone past without much comment other
>> than the odd "hey, works great", I don't really know where to take that.
>> 
>> Are you willing to review the patches?
>
> Well, I rarely ask about patches just for the sake of conversation. O:-)
>
> So yes, I am willing to review them -- and I suspect others are, as
> well. Nobody commented the V3 series on the U-Boot list -- save for
> Jon's comment about the series needing a rebase -- which could mean no
> one here is unhappy with them... or they were discussed and possibly
> acted upon on linux-sunxi, where the replies were redirected. I don't
> follow linux-sunx closely, so I couldn't tell. :)

No, so far there hasn't been much discussion, and people seem happy with
it. I have a couple of fixes lined up, but nothing major.

Also, a number of the patches are actually fixes that should really make
it into the U-Boot tree, no matter if the PSCI code is merged or
not. Some of them make the kernel go completely bonkers, other introduce
the risk of U-Boot falling over in style.

> Still, I am trying to figure out the whole Allwinner nebula and see how
> things are supposed to work out between their various SoCs and make
> sure to avoid duplicate/incompatible effort (you're mentioning the A20,
> there seems to be A31 work underway too elsewhere). I am starting to
> wonder whether an ARM allwinner sub-repo might make sense. Tom,
> Wolfgang?

Ian Campbell (cc-ed) is actively pushing out patches to support the A20
in mainline U-Boot (I believe you've been on the receiving end of
these), and I plan to rebase my series on top of his. Still, the A20
support is only a small part of the code, used as an example of how to
implement PSCI on a rather simple platform. This can easily be split out
and merged via different trees.

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny.