Re: [PATCH 1/3] arm64: Track system support for mixed endian EL0

[Suzuki K. Poulose]

On 16/01/15 16:15, Suzuki K. Poulose wrote:
> On 16/01/15 15:53, Will Deacon wrote:
> > On Thu, Jan 15, 2015 at 12:36:04PM +0000, Suzuki K. Poulose wrote:
> > > From: "Suzuki K. Poulose" <suzuki.poulose@xxxxxxx>
> > >
> > > This patch keeps track of the mixed endian EL0 support across
> > > the system and provides helper functions to export it. The status
> > > is a boolean indicating whether all the CPUs on the system supports
> > > mixed endian at EL0.
> > >
> > > Signed-off-by: Suzuki K. Poulose <suzuki.poulose@xxxxxxx>
> > > ---
> > >    arch/arm64/include/asm/cpufeature.h |   10 ++++++++++
> > >    arch/arm64/kernel/cpuinfo.c         |   22 ++++++++++++++++++++++
> > >    2 files changed, 32 insertions(+)
> > >
> > > diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
> > > index 07547cc..c7f68d1 100644
> > > --- a/arch/arm64/include/asm/cpufeature.h
> > > +++ b/arch/arm64/include/asm/cpufeature.h
> > > @@ -26,6 +26,9 @@
> > >
> > >    #define ARM64_NCAPS				2
> > >
> > > +#define ID_AA64MMFR0_EL1_BigEndEL0	(0x1UL << 16)
> > > +#define ID_AA64MMFR0_EL1_BigEnd		(0x1UL << 8)
> >
> > I don't like the CaMeLcAsE. Also, perhaps these definitions should be
> > somewhere like cputype.h?
> Yeah, I tried to keep it aligned withe ARMv8 architecture definition of
> those bits. Will change it.
> Things are a bit messy w.r.t the definitions. We have cpu.h,
> cpufeature.h and cputype.h. I could move it to cputype.h, where we
> already have MIDR_ defintions.
>
> > > +
> > >    #ifndef __ASSEMBLY__
> > >
> > >    extern DECLARE_BITMAP(cpu_hwcaps, ARM64_NCAPS);
> > > @@ -51,7 +54,14 @@ static inline void cpus_set_cap(unsigned int num)
> > >    		__set_bit(num, cpu_hwcaps);
> > >    }
> > >
> > > +static inline bool id_aa64mmfr0_mixed_endian_el0(unsigned long mmfr0)
> > > +{
> > > +	return !!(mmfr0 & (ID_AA64MMFR0_EL1_BigEndEL0 | ID_AA64MMFR0_EL1_BigEnd));
> > > +}
> >
> > These are 4-bit fields and I think you think you should be treating them
> > as such.
> OK
>
> > > +
> > >    void check_local_cpu_errata(void);
> > > +bool system_supports_mixed_endian_el0(void);
> > > +bool cpu_supports_mixed_endian_el0(void);
> > >
> > >    #endif /* __ASSEMBLY__ */
> > >
> > > diff --git a/arch/arm64/kernel/cpuinfo.c b/arch/arm64/kernel/cpuinfo.c
> > > index 07d435c..b6d1135 100644
> > > --- a/arch/arm64/kernel/cpuinfo.c
> > > +++ b/arch/arm64/kernel/cpuinfo.c
> > > @@ -35,6 +35,7 @@
> > >     */
> > >    DEFINE_PER_CPU(struct cpuinfo_arm64, cpu_data);
> > >    static struct cpuinfo_arm64 boot_cpu_data;
> > > +static bool mixed_endian_el0 = true;
> > >
> > >    static char *icache_policy_str[] = {
> > >    	[ICACHE_POLICY_RESERVED] = "RESERVED/UNKNOWN",
> > > @@ -68,6 +69,26 @@ static void cpuinfo_detect_icache_policy(struct cpuinfo_arm64 *info)
> > >    	pr_info("Detected %s I-cache on CPU%d\n", icache_policy_str[l1ip], cpu);
> > >    }
> > >
> > > +bool cpu_supports_mixed_endian_el0(void)
> > > +{
> > > +	return id_aa64mmfr0_mixed_endian_el0(read_cpuid(ID_AA64MMFR0_EL1));
> > > +}
> >
> > Can we not just define a mask/value pair and have code do the MMFR0 access
> > inline? It also feels a bit over-engineered like this.
> Sure, will change this.

On a second thought, we need the id_aa64mmfr0_mixed_endian_el0() for 
another code path. For a new CPU detected at boot time via 
cpuinfo_store_cpu(), where we get the 'filled' cpuinfo_arm64 which 
already has the id_aa64mmfr0. So we do:

+
+static void update_mixed_endian_el0_support(struct cpuinfo_arm64 *info)
+{
+	mixed_endian_el0 &= id_aa64mmfr0_mixed_endian_el0(info->reg_id_aa64mmfr0);
+}

So, having a helper to extract the support from the id_aa64mmfr0 makes 
it a bit more ordered.

But yes, we could switch to mask/value pair.

Thanks
Suzuki
> Thanks
> Suzuki
> > Will
>
>
> --
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo@xxxxxxxxxxxxxxx
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at  http://www.tux.org/lkml/


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/