From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933264AbcFJRCF (ORCPT ); Fri, 10 Jun 2016 13:02:05 -0400 Received: from foss.arm.com ([217.140.101.70]:39786 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753001AbcFJRCD (ORCPT ); Fri, 10 Jun 2016 13:02:03 -0400 Date: Fri, 10 Jun 2016 18:02:21 +0100 From: Will Deacon To: Suzuki K Poulose Cc: catalin.marinas@arm.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, steve.capper@linaro.org, Mark Rutland Subject: Re: [PATCH] arm64: cpuinfo: Expose MIDR_EL1 and REVIDR_EL1 to sysfs Message-ID: <20160610170220.GC23223@arm.com> References: <1465571984-18776-1-git-send-email-suzuki.poulose@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1465571984-18776-1-git-send-email-suzuki.poulose@arm.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jun 10, 2016 at 04:19:44PM +0100, Suzuki K Poulose wrote: > From: Steve Capper > > It can be useful for JIT software to be aware of MIDR_EL1 and > REVIDR_EL1 to ascertain the presence of any core errata that could > affect codegen. > > This patch exposes these registers through sysfs: > > /sys/devices/system/cpu/cpu$ID/identification/midr > /sys/devices/system/cpu/cpu$ID/identification/revidr > > where $ID is the cpu number. For big.LITTLE systems, one can have a > mixture of cores (e.g. Cortex A53 and Cortex A57), thus all CPUs need > to be enumerated. > > If the kernel does not have valid information to populate these entries > with, an empty string is returned to userspace. > > Cc: Catalin Marinas > Cc: Will Deacon > Cc: Mark Rutland > Signed-off-by: Steve Capper > [ Return error for access to !present CPU registers ] > Signed-off-by: Suzuki K. Poulose > --- > Changes since V2: > - Fix errno for failures (Spotted-by: Russell King) > - Roll back, if we encounter a missing cpu device > - Return error for access to registers of CPUs not present. > --- > arch/arm64/include/asm/cpu.h | 1 + > arch/arm64/kernel/cpuinfo.c | 69 ++++++++++++++++++++++++++++++++++++++++++++ > 2 files changed, 70 insertions(+) > > diff --git a/arch/arm64/include/asm/cpu.h b/arch/arm64/include/asm/cpu.h > index 13a6103..116a382 100644 > --- a/arch/arm64/include/asm/cpu.h > +++ b/arch/arm64/include/asm/cpu.h > @@ -29,6 +29,7 @@ struct cpuinfo_arm64 { > u32 reg_cntfrq; > u32 reg_dczid; > u32 reg_midr; > + u32 reg_revidr; > > u64 reg_id_aa64dfr0; > u64 reg_id_aa64dfr1; > diff --git a/arch/arm64/kernel/cpuinfo.c b/arch/arm64/kernel/cpuinfo.c > index c173d32..c2d0c42 100644 > --- a/arch/arm64/kernel/cpuinfo.c > +++ b/arch/arm64/kernel/cpuinfo.c > @@ -212,6 +212,7 @@ static void __cpuinfo_store_cpu(struct cpuinfo_arm64 *info) > info->reg_ctr = read_cpuid_cachetype(); > info->reg_dczid = read_cpuid(DCZID_EL0); > info->reg_midr = read_cpuid_id(); > + info->reg_revidr = read_cpuid(REVIDR_EL1); > > info->reg_id_aa64dfr0 = read_cpuid(ID_AA64DFR0_EL1); > info->reg_id_aa64dfr1 = read_cpuid(ID_AA64DFR1_EL1); > @@ -264,3 +265,71 @@ void __init cpuinfo_store_boot_cpu(void) > boot_cpu_data = *info; > init_cpu_features(&boot_cpu_data); > } > + > +#define CPUINFO_ATTR_RO(_name) \ > + static ssize_t show_##_name (struct device *dev, \ > + struct device_attribute *attr, char *buf) \ > + { \ > + struct cpuinfo_arm64 *info = &per_cpu(cpu_data, dev->id); \ > + if (!cpu_present(dev->id)) \ > + return -ENODEV; \ > + \ > + if (info->reg_midr) \ > + return sprintf(buf, "0x%016x\n", info->reg_##_name); \ Should this be 0x%08x, as these are 32-bit registers? > + else \ > + return 0; \ > + } \ > + static DEVICE_ATTR(_name, 0444, show_##_name, NULL) > + > +CPUINFO_ATTR_RO(midr); > +CPUINFO_ATTR_RO(revidr); > + > +static struct attribute *cpuregs_attrs[] = { > + &dev_attr_midr.attr, > + &dev_attr_revidr.attr, > + NULL > +}; > + > +static struct attribute_group cpuregs_attr_group = { > + .attrs = cpuregs_attrs, > + .name = "identification" > +}; > + > +static int __init cpuinfo_regs_init(void) > +{ > + int cpu, finalcpu, ret; > + struct device *dev; > + > + for_each_present_cpu(cpu) { > + dev = get_cpu_device(cpu); > + > + if (!dev) { > + ret = -ENODEV; > + break; > + } > + > + ret = sysfs_create_group(&dev->kobj, &cpuregs_attr_group); > + if (ret) > + break; > + } > + > + if (!ret) > + return 0; > + /* > + * We were unable to put down sysfs groups for all the CPUs, revert > + * all the groups we have placed down s.t. none are visible. > + * Otherwise we could give a misleading picture of what's present. > + */ > + finalcpu = cpu; > + for_each_present_cpu(cpu) { > + if (cpu == finalcpu) > + break; > + dev = get_cpu_device(cpu); > + if (dev) > + sysfs_remove_group(&dev->kobj, &cpuregs_attr_group); > + } Can CPUs be removed from underneath us using unregister_cpu? If so, I don't think we should assume that get_cpu_device will succeed in the same places for both the loops. Will