On Mon, Oct 26, 2020 at 07:02:50PM +0000, Qais Yousef wrote: > On 10/22/20 15:55, Greg Kroah-Hartman wrote: > > On Thu, Oct 22, 2020 at 02:47:52PM +0100, Qais Yousef wrote: > > > On 10/21/20 15:41, Will Deacon wrote: > > > > > We already expose MIDR and REVIDR via the current sysfs interface. We > > > > > can expand it to include _all_ the other ID_* regs currently available > > > > > to user via the MRS emulation and we won't have to debate what a new > > > > > interface would look like. The MRS emulation and the sysfs info should > > > > > probably match, though that means we need to expose the > > > > > ID_AA64PFR0_EL1.EL0 field which we currently don't. > > > > > > > > > > I do agree that an AArch32 cpumask is an easier option both from the > > > > > kernel implementation perspective and from the application usability > > > > > one, though not as easy as automatic task placement by the scheduler (my > > > > > first preference, followed by the id_* regs and the aarch32 mask, though > > > > > not a strong preference for any). > > > > > > > > If a cpumask is easier to implement and easier to use, then I think that's > > > > what we should do. It's also then dead easy to disable if necessary by > > > > just returning 0. The only alternative I would prefer is not having to > > > > expose this information altogether, but I'm not sure that figuring this > > > > out from MIDR/REVIDR alone is reliable. > > > > > > So the mask idea is about adding a new > > > > > > /sys/devices/system/cpu/aarch32_cpus > > > > > > ? > > > > Is this a file, a directory, or what? What's the contents? > > > > Without any of that, I have no idea if it's "ok" or not... > > Hopefully the below patch explains better. Note that I added the new attribute > to driver/base/cpu.c, but assuming we will still want to go down this route, we > will need a generic way for archs to add their attributes to > /sys/devices/system/cpu/. > > Something like having a special define for archs to append their own > attributes list > > #define SYSFS_SYSTEM_CPU_ARCH_ATTRIBUTES > > Or probably there's a way to add this file (attribute) dynamically from arch > code that I just didn't figure out how to do yet. Please do that, sysfs files should not be present when the information is not needed from them. Look at the is_visible() callback for the attribute for how to do it. > > Thanks > > -- > Qais Yousef > > > ---------->8------------ > > >From 96dfdfdacb2a26a60ba19051e8c72e839eb5408b Mon Sep 17 00:00:00 2001 > From: Qais Yousef <qais.yousef@xxxxxxx> > Date: Mon, 26 Oct 2020 16:33:32 +0000 > Subject: [PATCH] arm64: export aarch32_online mask in sysfs > > This patch to be applied on top of arm64 Asymmetric AArch32 support. > > It explores the option of exporting the AArch32 capable cpus as a mask > on sysfs. > > This is to help drive the discussion on the API before sending the next > version which I yet to address some of the review comments. > > The output looks like: > > # cat /sys/devices/system/cpu/aarch32_online > 0-5 > > Signed-off-by: Qais Yousef <qais.yousef@xxxxxxx> > --- > Documentation/ABI/testing/sysfs-devices-system-cpu | 7 +++++++ > arch/arm64/include/asm/cpufeature.h | 2 ++ > arch/arm64/kernel/cpufeature.c | 8 ++++++++ > drivers/base/cpu.c | 12 ++++++++++++ > 4 files changed, 29 insertions(+) > > diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu > index b555df825447..9ccb5c3f5ee3 100644 > --- a/Documentation/ABI/testing/sysfs-devices-system-cpu > +++ b/Documentation/ABI/testing/sysfs-devices-system-cpu > @@ -36,6 +36,13 @@ Description: CPU topology files that describe kernel limits related to > > See Documentation/admin-guide/cputopology.rst for more information. > > +What: /sys/devices/system/cpu/aarch32_online > +Date: October 2020 > +Contact: Linux ARM Kernel Mailing list <linux-arm-kernel@xxxxxxxxxxxxxxxxxxx> > +Description: CPU topology file that describes which cpus support AArch32 at > + EL0. Only available on arm64. > + > + The value is updated when a cpu becomes online then sticks. What does "then sticks" mean? > > What: /sys/devices/system/cpu/probe > /sys/devices/system/cpu/release > diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h > index 2b87f17b2bd4..edd18002ad81 100644 > --- a/arch/arm64/include/asm/cpufeature.h > +++ b/arch/arm64/include/asm/cpufeature.h > @@ -380,6 +380,8 @@ cpucap_multi_entry_cap_matches(const struct arm64_cpu_capabilities *entry, > return false; > } > > +extern cpumask_t aarch32_el0_mask; > + > extern DECLARE_BITMAP(cpu_hwcaps, ARM64_NCAPS); > extern struct static_key_false cpu_hwcap_keys[ARM64_NCAPS]; > extern struct static_key_false arm64_const_caps_ready; > diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c > index 0f7307c8ad80..662bbc2b15cd 100644 > --- a/arch/arm64/kernel/cpufeature.c > +++ b/arch/arm64/kernel/cpufeature.c > @@ -1723,6 +1723,13 @@ cpucap_panic_on_conflict(const struct arm64_cpu_capabilities *cap) > return !!(cap->type & ARM64_CPUCAP_PANIC_ON_CONFLICT); > } > > +cpumask_t aarch32_el0_mask; > +static void cpu_enable_aarch32_el0(struct arm64_cpu_capabilities const *cap) > +{ > + if (has_cpuid_feature(cap, SCOPE_LOCAL_CPU)) > + cpumask_set_cpu(smp_processor_id(), &aarch32_el0_mask); > +} > + > static const struct arm64_cpu_capabilities arm64_features[] = { > { > .desc = "GIC system register CPU interface", > @@ -1809,6 +1816,7 @@ static const struct arm64_cpu_capabilities arm64_features[] = { > { > .capability = ARM64_HAS_ASYM_32BIT_EL0, > .type = ARM64_CPUCAP_WEAK_LOCAL_CPU_FEATURE, > + .cpu_enable = cpu_enable_aarch32_el0, > .matches = has_cpuid_feature, > .sys_reg = SYS_ID_AA64PFR0_EL1, > .sign = FTR_UNSIGNED, > diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c > index d2136ab9b14a..569baacde508 100644 > --- a/drivers/base/cpu.c > +++ b/drivers/base/cpu.c > @@ -459,6 +459,15 @@ EXPORT_SYMBOL_GPL(cpu_device_create); > static DEVICE_ATTR(modalias, 0444, print_cpu_modalias, NULL); > #endif > > +#ifdef CONFIG_ARM64 > +static ssize_t print_aarch32_online(struct device *dev, > + struct device_attribute *attr, char *buf) > +{ > + return cpumap_print_to_pagebuf(true, buf, &aarch32_el0_mask); > +} > +static DEVICE_ATTR(aarch32_online, 0444, print_aarch32_online, NULL); DEVICE_ATTR_RO()? > +#endif Hah, no, no arch-specific stuff in here, sorry. Please do this properly in your arch-specific code only. thanks, greg k-h