imx6q restart is broken

[Shawn Guo]

On Thu, Aug 09, 2012 at 11:18:47AM +0800, Hui Wang wrote:
> Dirk Behme wrote:
> >On 08.08.2012 12:18, Shawn Guo wrote:
> >>Thanks Dirk for reporting that imx6q restart (reboot command) is broken.
> >>
> >>I tracked down the issue a little bit and found imx6q_restart hangs
> >>on the of_iomap/ioremap call. The following change, moving the call
> >>somewhere else than imx6q_restart, will just fix the problem.
> >>
> >>Does that mean ioremap call is not allowed in platform restart hook?
> >>I'm not sure about that, because I found it works just fine if I build
> >>imx_v6_v7_defconfig with V6 (imx3) platforms excluded (IOW, build a V7
> >>only kernel - imx5 and imx6), which is the case how I tested imx6q
> >>restart feature when I was adding it.
> >>
> >>To summarize, the imx6q_restart hangs at ioremap call on a V6 + V7
> >>kernel, while it works fine on a V7 only image. I need some help to
> >>understand that.
> >
> >Some additional information from my debugging:
> >
> >a) Having a JTAG debugger attached to the i.MX6 SabreLite board I
> >use (kernel built with imx_v6_v7_defconfig) the reboot does work.
> >No hang. This does mean I can't debug the reboot hang with a JTAG
> >debugger. Therefore I added some printk debugging:
> >
> >b) Adding some printk statements [1] in the of_iomap/ioremap call,
> >it looks to me that the system hangs in
> >
> >of_iomap() -> ... -> set_pte_at() -> set_pte_ext() /
> >cpu_v7_set_pte_ext() <= hang
> >
> I noticed this problem several weeks ago, and did some debug, what i
> found is following:
> 
Thanks for these great findings.  I also just tracked it down to that
cpu_v7_set_pte_ext hangs on

	mcr   p15, 0, r0, c7, c10, 1          @ flush_pte

> - at the last stage of reset, all non-boot cpus will call
> ipi_cpu_stop()->cpu_relax(), the cpu_relax() is defined to smp_mb()
> for V6, and smp_mb() is defined to dmb ("mcr p15, 0, %0, c7, c10,
> 5")
> 
> - the boot cpu will call cpu_v7_set_pte_ext() in the
> proc-v7-2level.S, at the end of this function, boot cpu will call
> flush_pte (mcr p15, 0, r0, c7, c10, 1), after executing this
> function, the system will hang. That is to say, all non-boot cpus
> repeatedly call ("mcr p15, 0, %0, c7, c10, 5"), if boot cpu call
> flush_pte (mcr p15, 0, r0, c7, c10, 1), the system will hang, this
> occurs on the cortexa9 r2p10 cpus (freescale i.MX6Q), i don't know
> the root cause for this problem, but if we split imx_v6_v7_defconfig
> into v7_only and use v7_only to build kernel image for imx6q, this
> problem will disappear, since the cpu_relax() will be defined to
> barrier().
> 
> - i think we should split imx_v6_v7_defconfig into v6_only and
> v7_only, since when we use imx_v6_v7_defconfig, we will introduce
> "-D__LINUX_ARM_ARCH__=6" unconditionally, this macro is OK for V6
> platforms (imx3), but it is not good for V7 platforms (imx5, imx6).
> lets grep "__LINUX_ARM_ARCH__" occurrence under the arch/arm, all
> (#if __LINUX_ARM_ARCH__ == 6) and (#if __LINUX_ARM_ARCH__ >= 7)
> occurrence will affect V7 platforms.

I just copied a few more people.  Let's hear their comments.

Regards,
Shawn