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    SubjectRe: [RFC PATCH] ARM: Add imprecise abort enable/disable macro
    On 02/10/2014 03:16 PM, Dave Martin wrote:
    > On Fri, Feb 07, 2014 at 05:19:15PM +0100, Fabrice GASNIER wrote:
    >> This patch adds imprecise abort enable/disable macros.
    >> It also enables imprecise aborts when starting kernel.
    > Relying on imprecise aborts for hardware probing would be considered bad
    > hardware and/or software design for ARM-specific stuff.
    >
    > PCI is more generic though, so we may have to put up with this to some
    > extent. Can you point me to the affected probing code? I'm not very
    > familiar with that stuff...
    Hi,

    I'm currently re-basing to prepare upstream of such a driver so, no code
    for now on my side,
    but, I saw others that have similar behavior :
    http://www.spinics.net/lists/linux-pci/msg26124.html
    Basically, I think all PCI drivers using hook_fault_code(16+6, ...) use
    similar mechanism.
    >
    >> Signed-off-by: Fabrice Gasnier <fabrice.gasnier@st.com>
    >> ---
    >> arch/arm/include/asm/irqflags.h | 33 +++++++++++++++++++++++++++++++++
    >> arch/arm/kernel/smp.c | 1 +
    >> arch/arm/kernel/traps.c | 4 ++++
    >> 3 files changed, 38 insertions(+)
    >>
    >> diff --git a/arch/arm/include/asm/irqflags.h b/arch/arm/include/asm/irqflags.h
    >> index 3b763d6..82e3834 100644
    >> --- a/arch/arm/include/asm/irqflags.h
    >> +++ b/arch/arm/include/asm/irqflags.h
    >> @@ -51,6 +51,9 @@ static inline void arch_local_irq_disable(void)
    >>
    >> #define local_fiq_enable() __asm__("cpsie f @ __stf" : : : "memory", "cc")
    >> #define local_fiq_disable() __asm__("cpsid f @ __clf" : : : "memory", "cc")
    >> +
    >> +#define local_abt_enable() __asm__("cpsie a @ __sta" : : : "memory", "cc")
    >> +#define local_abt_disable() __asm__("cpsid a @ __cla" : : : "memory", "cc")
    >> #else
    >>
    >> /*
    >> @@ -130,6 +133,36 @@ static inline void arch_local_irq_disable(void)
    >> : "memory", "cc"); \
    >> })
    >>
    >> +/*
    >> + * Enable Aborts
    >> + */
    >> +#define local_abt_enable() \
    >> + ({ \
    >> + unsigned long temp; \
    >> + __asm__ __volatile__( \
    >> + "mrs %0, cpsr @ sta\n" \
    >> +" bic %0, %0, %1\n" \
    >> +" msr cpsr_c, %0" \
    > I suggest you use "cpsie/cpsid a" instead. This requires ARMv6, but the
    > CPSR.A bit only exists on ARMv6 and later anyway. Poking that bit
    > on earlier CPUs may cause unpredictable behaviour, so these macros
    > should be no-ops for v5 and earlier.
    Thanks,
    I'll prepare a new patch that way.
    >
    >> + : "=r" (temp) \
    >> + : "r" (PSR_A_BIT) \
    >> + : "memory", "cc"); \
    >> + })
    >> +
    >> +/*
    >> + * Disable Aborts
    >> + */
    >> +#define local_abt_disable() \
    >> + ({ \
    >> + unsigned long temp; \
    >> + __asm__ __volatile__( \
    >> + "mrs %0, cpsr @ cla\n" \
    >> +" orr %0, %0, %1\n" \
    >> +" msr cpsr_c, %0" \
    >> + : "=r" (temp) \
    >> + : "r" (PSR_A_BIT) \
    >> + : "memory", "cc"); \
    >> + })
    >> +
    >> #endif
    >>
    >> /*
    >> diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c
    >> index dc894ab..c2093cb 100644
    >> --- a/arch/arm/kernel/smp.c
    >> +++ b/arch/arm/kernel/smp.c
    >> @@ -377,6 +377,7 @@ asmlinkage void secondary_start_kernel(void)
    >>
    >> local_irq_enable();
    >> local_fiq_enable();
    >> + local_abt_enable();
    >>
    >> /*
    >> * OK, it's off to the idle thread for us
    >> diff --git a/arch/arm/kernel/traps.c b/arch/arm/kernel/traps.c
    >> index 4636d56..ef15709 100644
    >> --- a/arch/arm/kernel/traps.c
    >> +++ b/arch/arm/kernel/traps.c
    >> @@ -900,6 +900,10 @@ void __init early_trap_init(void *vectors_base)
    >>
    >> flush_icache_range(vectors, vectors + PAGE_SIZE * 2);
    >> modify_domain(DOMAIN_USER, DOMAIN_CLIENT);
    >> +
    >> + /* Enable imprecise aborts */
    >> + local_abt_enable();
    > It would be good to clean up why aborts are not being consistently
    > enabled on boot.
    I did a bit of analysis and summarized it in this thread. I've not been
    further:
    http://archive.arm.linux.org.uk/lurker/message/20140203.164322.edba427a.en.html

    BR,
    Fabrice
    >
    > Really, they should be enabled, except for a brief window during
    > boot when the vectors are not mapped and the abort can't be dispatched.
    >
    > Cheers
    > ---Dave



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