Re: [PATCH 12/14] arm64: Check for selected granule support

[Suzuki K. Poulose]

On 13/08/15 13:28, Steve Capper wrote:
> On 13 August 2015 at 12:34, Suzuki K. Poulose <suzuki.poulose@xxxxxxx> wrote:
> > From: "Suzuki K. Poulose" <suzuki.poulose@xxxxxxx>
> >
> > Ensure that the selected page size is supported by the
> > CPU(s).
> >
> > Cc: Mark Rutland <mark.rutland@xxxxxxx>
> > Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
> > Cc: Will Deacon <will.deacon@xxxxxxx>
> > Signed-off-by: Suzuki K. Poulose <suzuki.poulose@xxxxxxx>
> > ---
> >   arch/arm64/include/asm/sysreg.h |    6 ++++++
> >   arch/arm64/kernel/head.S        |   24 +++++++++++++++++++++++-
> >   2 files changed, 29 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/arm64/include/asm/sysreg.h b/arch/arm64/include/asm/sysreg.h
> > index a7f3d4b..e01d323 100644
> > --- a/arch/arm64/include/asm/sysreg.h
> > +++ b/arch/arm64/include/asm/sysreg.h
> > @@ -87,4 +87,10 @@ static inline void config_sctlr_el1(u32 clear, u32 set)
> >   }
> >   #endif
> >
> > +#define ID_AA64MMFR0_TGran4_SHIFT      28
> > +#define ID_AA64MMFR0_TGran64_SHIFT     24
> > +
> > +#define ID_AA64MMFR0_TGran4_ENABLED    0x0
> > +#define ID_AA64MMFR0_TGran64_ENABLED   0x0
> > +
> >   #endif /* __ASM_SYSREG_H */
> > diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
> > index 01b8e58..0cb04db 100644
> > --- a/arch/arm64/kernel/head.S
> > +++ b/arch/arm64/kernel/head.S
> > @@ -31,10 +31,11 @@
> >   #include <asm/cputype.h>
> >   #include <asm/kernel-pgtable.h>
> >   #include <asm/memory.h>
> > -#include <asm/thread_info.h>
> >   #include <asm/pgtable-hwdef.h>
> >   #include <asm/pgtable.h>
> >   #include <asm/page.h>
> > +#include <asm/sysreg.h>
> > +#include <asm/thread_info.h>
> >   #include <asm/virt.h>
> >
> >   #define __PHYS_OFFSET  (KERNEL_START - TEXT_OFFSET)
> > @@ -606,9 +607,25 @@ ENDPROC(__secondary_switched)
> >    *  x27 = *virtual* address to jump to upon completion
> >    *
> >    * other registers depend on the function called upon completion
> > + * Checks if the selected granule size is supported by the CPU.
> >    */
> > +#if    defined(CONFIG_ARM64_64K_PAGES)
> > +
> > +#define ID_AA64MMFR0_TGran_SHIFT       ID_AA64MMFR0_TGran64_SHIFT
> > +#define ID_AA64MMFR0_TGran_ENABLED     ID_AA64MMFR0_TGran64_ENABLED
> > +
> > +#else
> > +
> > +#define ID_AA64MMFR0_TGran_SHIFT       ID_AA64MMFR0_TGran4_SHIFT
> > +#define ID_AA64MMFR0_TGran_ENABLED     ID_AA64MMFR0_TGran4_ENABLED
> > +
> > +#endif
> >          .section        ".idmap.text", "ax"
> >   __enable_mmu:
> > +       mrs     x1, ID_AA64MMFR0_EL1
> > +       ubfx    x2, x1, #ID_AA64MMFR0_TGran_SHIFT, 4
> > +       cmp     x2, #ID_AA64MMFR0_TGran_ENABLED
> > +       b.ne    __no_granule_support
> >          ldr     x5, =vectors
> >          msr     vbar_el1, x5
> >          msr     ttbr0_el1, x25                  // load TTBR0
> > @@ -626,3 +643,8 @@ __enable_mmu:
> >          isb
> >          br      x27
> >   ENDPROC(__enable_mmu)
> > +
> > +__no_granule_support:
> > +       wfe
> > +       b __no_granule_support
> > +ENDPROC(__no_granule_support)
> > --
> > 1.7.9.5
>
> Hi Suzuki,
> Is is possible to tell the user that the kernel has failed to boot due
> to the kernel granule being unsupported?

We don't have anything up at this time. The "looping address" is actually a clue
to the (expert) user. Not sure we can do something, until we get something like DEBUG_LL(?)
Or we should let it continue and end in a panic(?). The current situation can boot a
multi-cluster system with boot cluster having the Tgran support(which doesn't make a
strong use case though). I will try out some options and get back to you.


Thanks
Suzuki

> Cheers,
> --
> Steve

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