Re: [PATCH] ARM: EXYNOS: Fix incorrect usage of S5P_ARM_CORE1_*registers

[Lorenzo Pieralisi]

On Wed, Jun 19, 2013 at 01:50:57PM +0100, Tomasz Figa wrote:
> On Wednesday 19 of June 2013 17:39:21 Chander Kashyap wrote:
> > On 18 June 2013 23:29, Kukjin Kim <kgene.kim@xxxxxxxxxxx> wrote:
> > > On 06/19/13 02:45, Tomasz Figa wrote:
> > >> Ccing Arnd and Olof, because I forgot to add them to git send-email...
> > >> 
> > >> Sorry for the noise.
> > >> 
> > >> On Tuesday 18 of June 2013 17:26:31 Tomasz Figa wrote:
> > >>> S5P_ARM_CORE1_* registers affect only core 1. To control further
> > >>> cores
> > >>> properly another registers must be used.
> > >>> 
> > >>> This patch replaces S5P_ARM_CORE1_* register definitions with
> > >>> S5P_ARM_CORE_*(x) macro which return addresses of registers for
> > >>> specified core.
> > >>> 
> > >>> This fixes CPU hotplug on quad core Exynos SoCs on which currently
> > >>> offlining CPUs 2 or 3 caused CPU 1 to be turned off.
> > >> 
> > >> Obviously this doesn't happen currently because of the if (cpu == 1),
> > >> but> 
> > > Yes, not happened...and just note exynos5440 doesn't support hotplug :)
> > > so this is available on exynos4412 and added 5420.
> > > 
> > >> if logical cpu1 turned out not to be physical cpu1, then it would
> > >> crash.
> > >> 
> > >> Best regards,
> > >> Tomasz
> > >> 
> > >>> In addition,
> > >>> bring-up of CPU 2 and 3 is fixed on boards where bootloader powers
> > >>> off
> > >>> secondary cores by default.
> > > 
> > > I need to test on board about above...
> > > 
> > >>> Cc: stable@xxxxxxxxxxxxxxx
> > >>> Signed-off-by: Tomasz Figa<t.figa@xxxxxxxxxxx>
> > >>> Signed-off-by: Kyungmin Park<kyungmin.park@xxxxxxxxxxx>
> > >>> ---
> > >>> 
> > >>>   arch/arm/mach-exynos/hotplug.c               |  9 +++++----
> > >>>   arch/arm/mach-exynos/include/mach/regs-pmu.h | 10 +++++++---
> > >>>   arch/arm/mach-exynos/platsmp.c               |  9 +++++----
> > >>>   3 files changed, 17 insertions(+), 11 deletions(-)
> > >>> 
> > >>> diff --git a/arch/arm/mach-exynos/hotplug.c
> > >>> b/arch/arm/mach-exynos/hotplug.c index af90cfa..c089943 100644
> > >>> --- a/arch/arm/mach-exynos/hotplug.c
> > >>> +++ b/arch/arm/mach-exynos/hotplug.c
> > >>> @@ -93,10 +93,11 @@ static inline void cpu_leave_lowpower(void)
> > >>> 
> > >>>   static inline void platform_do_lowpower(unsigned int cpu, int
> > >>> 
> > >>> *spurious) {
> > >>> 
> > >>>         for (;;) {
> > >>> 
> > >>> +               void __iomem *reg_base;
> > >>> +               unsigned int phys_cpu = cpu_logical_map(cpu);
> > >>> 
> > >>> -               /* make cpu1 to be turned off at next WFI command */
> > >>> -               if (cpu == 1)
> > >>> -                       __raw_writel(0, S5P_ARM_CORE1_CONFIGURATION);
> > >>> +               reg_base = S5P_ARM_CORE_CONFIGURATION(phys_cpu);
> > 
> > Tomasz,
> > This will break for non-zero, MPIDR value.  Say if MPIDR is 1 then for
> > cpu0 phys_cpu value will be 0x100,
> > and address calculation will be   (S5P_ARM_CORE0_CONFIGURATION +
> > ((0x101) * 0x80)), which is wrong.

Honestly, I did not understand the reasoning above, please clarify.

> 
> Hmm, according to the code initializing __cpu_logical_map[] array this is 
> not true.
> 
> Here's the code:
> 
> https://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git/tree/arch/arm/kernel/setup.c?id=refs/tags/next-20130619#n468
> 
> and for used macros and bitmasks:
> 
> https://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git/tree/arch/arm/include/asm/cputype.h?id=refs/tags/next-20130619#n45
> 
> Now the structure of the MPIDR register:
> 
> http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ddi0388e/CIHEBGFG.html
> 
> As you can see, the value read from the register in 
> smp_setup_processor_id() is only the physical CPU ID, so I don't see any 
> problem here.

Define "physical CPU ID" :-)

There is a problem here: the MPIDR is not an index, and the cpu_logical_map is
populated in arm_dt_init_cpu_maps in:

https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/arch/arm/kernel/devtree.c?id=refs/tags/v3.10-rc6

with all affinity levels.

You need to perform a mapping between logical cpus and registers offset,
you can't use the cpu_logical_map directly for that.

Next accident waiting to happen is GIC code (CONFIG_GIC_NON_BANKED), where
cpu_logical_map is used erroneously as an index.

Lorenzo

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