Messages in this thread | | | Date | Tue, 30 Sep 2014 17:03:31 +0100 | From | Will Deacon <> | Subject | Re: [PATCH/RFC v2 1/4] ARM: hw_breakpoint: Add arm_dbg_regs_available flag |
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Hi Geert,
On Tue, Sep 30, 2014 at 01:26:24PM +0100, Geert Uytterhoeven wrote: > If power area D4, which contains the Coresight-ETM hardware block, is > powered down on R-Mobile A1 (r8a7740), the kernel crashes when > suspending from s2ram with: > > Internal error: Oops - undefined instruction: 0 [#1] ARM > > This happens because dbg_cpu_pm_notify() calls reset_ctrl_regs(), which > can't access the debug registers as the debug module is powered down. > > As suggested by Russell King, track whether the ETM block is powered down > to fix this. > > The availability of the debug registers depends on the platform and its > state. Hence provide a mechanism for platform code to indicate that the > debug registers are available or not, using a boolean flag that defaults > to true. > > Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be> > --- > v2: > - New > > arch/arm/include/asm/hw_breakpoint.h | 2 ++ > arch/arm/kernel/hw_breakpoint.c | 7 +++++++ > 2 files changed, 9 insertions(+) > > diff --git a/arch/arm/include/asm/hw_breakpoint.h b/arch/arm/include/asm/hw_breakpoint.h > index 8e427c7b44257d2d..51ffdae41bfe3754 100644 > --- a/arch/arm/include/asm/hw_breakpoint.h > +++ b/arch/arm/include/asm/hw_breakpoint.h > @@ -110,6 +110,8 @@ static inline void decode_ctrl_reg(u32 reg, > asm volatile("mcr p14, 0, %0, " #N "," #M ", " #OP2 : : "r" (VAL));\ > } while (0) > > +extern bool arm_dbg_regs_available; > + > struct notifier_block; > struct perf_event; > struct pmu; > diff --git a/arch/arm/kernel/hw_breakpoint.c b/arch/arm/kernel/hw_breakpoint.c > index b5b452f90f761bd2..96193c0165fbe5ca 100644 > --- a/arch/arm/kernel/hw_breakpoint.c > +++ b/arch/arm/kernel/hw_breakpoint.c > @@ -38,6 +38,8 @@ > #include <asm/traps.h> > #include <asm/hardware/coresight.h> > > +bool arm_dbg_regs_available = true; > + > /* Breakpoint currently in use for each BRP. */ > static DEFINE_PER_CPU(struct perf_event *, bp_on_reg[ARM_MAX_BRP]); > > @@ -931,6 +933,11 @@ static void reset_ctrl_regs(void *unused) > int i, raw_num_brps, err = 0, cpu = smp_processor_id(); > u32 val; > > + if (!arm_dbg_regs_available) { > + pr_warn_once("Debug registers are not available\n"); > + return; > + }
Whilst I guess this solves your problem, it doesn't feel like a scalable fix for something that can/will assumedly happen elsewhere in an SoC (e.g. PMU registers in perf). I'd much rather have a generic abstraction for power domains, which subsystems such as hw_breakpoint can attempt to take a reference on when they want to access registers in that domain.
Will
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