[RFC/PATCH 0/3] ARM: Use udiv/sdiv for __aeabi_{u}idiv library functions

Russell King - ARM Linux
2015-11-24T10:39:48Z

On Tue, Nov 24, 2015 at 12:53:49AM -0800, Stephen Boyd wrote:
> On 11/23, Stephen Boyd wrote:
> > On 11/23, Arnd Bergmann wrote:
> > >
> > > Ok, thanks for the confirmation.
> > >
> > > Summarizing what we've found, I think we can get away with just
> > > introducing two Kconfig symbols ARCH_MULTI_V7VE and CPU_V7VE.
> > > Most CPUs fall clearly into one category or the other, and then
> > > we can allow LPAE to be selected for V7VE-only build but not
> > > for plain V7, and we can unconditionally build the kernel with
> > >
> > > arch-$(CONFIG_CPU_32v7VE) = -D__LINUX_ARM_ARCH__=7 $(call cc-option,-march=armv7ve,-march=armv7-a -mcpu=cortex-a15)
> > >
> >
> > This causes compiler spew for me:
> >
> > warning: switch -mcpu=cortex-a15 conflicts with -march=armv7-a switch
> >
> > Removing -march=armv7-a from there makes it quiet.
> >
> > Also, it's sort of feels wrong to have -mcpu in a place where
> > we're exclusively doing -march. Perhaps the fallback should be
> > bog standard -march=armv7-a? (or the fallback for that one
> > "-march=armv5t -Wa$(comma)-march=armv7-a")?
> >
>
> And adding CPU_V7VE causes a cascade of changes to wherever
> CPU_V7 is being used today. Here's the patch I currently have,
> without the platform changes:
>
> ---8<----
> arch/arm/Kconfig | 68 +++++++++++++++++++++-----------------
> arch/arm/Kconfig-nommu | 2 +-
> arch/arm/Makefile | 1 +
> arch/arm/boot/compressed/head.S | 2 +-
> arch/arm/boot/compressed/misc.c | 2 +-
> arch/arm/include/asm/cacheflush.h | 2 +-
> arch/arm/include/asm/glue-cache.h | 2 +-
> arch/arm/include/asm/glue-proc.h | 2 +-
> arch/arm/include/asm/switch_to.h | 2 +-
> arch/arm/include/debug/icedcc.S | 2 +-
> arch/arm/kernel/entry-armv.S | 6 ++--
> arch/arm/kernel/perf_event_v7.c | 4 +--
> arch/arm/kvm/Kconfig | 2 +-
> arch/arm/mm/Kconfig | 41 ++++++++++++++++-------
> arch/arm/mm/Makefile | 1 +
> arch/arm/probes/kprobes/test-arm.c | 2 +-
> drivers/bus/Kconfig | 6 ++--
> 17 files changed, 86 insertions(+), 61 deletions(-)
>
> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> index 9e2d2adcc85b..ccd0d5553d38 100644
> --- a/arch/arm/Kconfig
> +++ b/arch/arm/Kconfig
> @@ -32,7 +32,7 @@ config ARM
> select HANDLE_DOMAIN_IRQ
> select HARDIRQS_SW_RESEND
> select HAVE_ARCH_AUDITSYSCALL if (AEABI && !OABI_COMPAT)
> - select HAVE_ARCH_BITREVERSE if (CPU_32v7M || CPU_32v7) && !CPU_32v6
> + select HAVE_ARCH_BITREVERSE if (CPU_32v7M || CPU_32v7 || CPU_32_v7VE) && !CPU_32v6
> select HAVE_ARCH_JUMP_LABEL if !XIP_KERNEL && !CPU_ENDIAN_BE32
> select HAVE_ARCH_KGDB if !CPU_ENDIAN_BE32
> select HAVE_ARCH_SECCOMP_FILTER if (AEABI && !OABI_COMPAT)
> @@ -46,12 +46,12 @@ config ARM
> select HAVE_DMA_ATTRS
> select HAVE_DMA_CONTIGUOUS if MMU
> select HAVE_DYNAMIC_FTRACE if (!XIP_KERNEL) && !CPU_ENDIAN_BE32
> - select HAVE_EFFICIENT_UNALIGNED_ACCESS if (CPU_V6 || CPU_V6K || CPU_V7) && MMU
> + select HAVE_EFFICIENT_UNALIGNED_ACCESS if (CPU_V6 || CPU_V6K || CPU_V7 || CPU_V7VE) && MMU
> select HAVE_FTRACE_MCOUNT_RECORD if (!XIP_KERNEL)
> select HAVE_FUNCTION_GRAPH_TRACER if (!THUMB2_KERNEL)
> select HAVE_FUNCTION_TRACER if (!XIP_KERNEL)
> select HAVE_GENERIC_DMA_COHERENT
> - select HAVE_HW_BREAKPOINT if (PERF_EVENTS && (CPU_V6 || CPU_V6K || CPU_V7))
> + select HAVE_HW_BREAKPOINT if (PERF_EVENTS && (CPU_V6 || CPU_V6K || CPU_V7 || CPU_V7VE))
> select HAVE_IDE if PCI || ISA || PCMCIA
> select HAVE_IRQ_TIME_ACCOUNTING
> select HAVE_KERNEL_GZIP
> @@ -805,6 +805,12 @@ config ARCH_MULTI_V7
> select CPU_V7
> select HAVE_SMP
>
> +config ARCH_MULTI_V7VE
> + bool "ARMv7 w/ virtualization extensions based platforms (Cortex-A, PJ4-MP, Krait)"
> + select ARCH_MULTI_V6_V7
> + select CPU_V7VE
> + select HAVE_SMP
> +
> config ARCH_MULTI_V6_V7
> bool
> select MIGHT_HAVE_CACHE_L2X0
> @@ -1069,7 +1075,7 @@ config ARM_ERRATA_411920
>
> config ARM_ERRATA_430973
> bool "ARM errata: Stale prediction on replaced interworking branch"
> - depends on CPU_V7
> + depends on CPU_V7 || CPU_V7VE

NAK on all this. The fact that you're having to add CPU_V7VE at all
sites which have CPU_V7 shows that this is a totally broken way of
approaching this.

Make CPU_V7VE be an _add-on_ to CPU_V7. In other words, when CPU_V7VE
is enabled, CPU_V7 should also be enabled, just like we do for CPU_V6K.

Note that v7M is different because that's not an add-on feature, it's
a different CPU class from (what should be) v7A.

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