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Wed, 21 Oct 2020 12:46:46 +0100 MIME-Version: 1.0 Date: Wed, 21 Oct 2020 12:46:46 +0100 From: Marc Zyngier To: Greg Kroah-Hartman Subject: Re: [RFC PATCH v2 4/4] arm64: Export id_aar64fpr0 via sysfs In-Reply-To: <20201021112519.GA1141598@kroah.com> References: <20201021104611.2744565-1-qais.yousef@arm.com> <20201021104611.2744565-5-qais.yousef@arm.com> <63fead90e91e08a1b173792b06995765@kernel.org> <20201021112519.GA1141598@kroah.com> User-Agent: Roundcube Webmail/1.4.9 Message-ID: X-Sender: maz@kernel.org X-SA-Exim-Connect-IP: 51.254.78.96 X-SA-Exim-Rcpt-To: gregkh@linuxfoundation.org, qais.yousef@arm.com, catalin.marinas@arm.com, will@kernel.org, peterz@infradead.org, morten.rasmussen@arm.com, torvalds@linux-foundation.org, james.morse@arm.com, linux-arm-kernel@lists.infradead.org, linux-arch@vger.kernel.org X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20201021_074649_937962_015DE52E X-CRM114-Status: GOOD ( 24.35 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-arch@vger.kernel.org, Will Deacon , "Peter Zijlstra \(Intel\)" , Catalin Marinas , Morten Rasmussen , James Morse , Linus Torvalds , Qais Yousef , linux-arm-kernel@lists.infradead.org Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 2020-10-21 12:25, Greg Kroah-Hartman wrote: > On Wed, Oct 21, 2020 at 12:09:58PM +0100, Marc Zyngier wrote: >> On 2020-10-21 11:46, Qais Yousef wrote: >> > So that userspace can detect if the cpu has aarch32 support at EL0. >> > >> > CPUREGS_ATTR_RO() was renamed to CPUREGS_RAW_ATTR_RO() to better reflect >> > what it does. And fixed to accept both u64 and u32 without causing the >> > printf to print out a warning about mismatched type. This was caught >> > while testing to check the new CPUREGS_USER_ATTR_RO(). >> > >> > The new CPUREGS_USER_ATTR_RO() exports a Sanitised or RAW sys_reg based >> > on a @cond to user space. The exported fields match the definition in >> > arm64_ftr_reg so that the content of a register exported via MRS and >> > sysfs are kept cohesive. >> > >> > The @cond in our case is that the system is asymmetric aarch32 and the >> > controlling sysctl.enable_asym_32bit is enabled. >> > >> > Update Documentation/arm64/cpu-feature-registers.rst to reflect the >> > newly visible EL0 field in ID_AA64FPR0_EL1. >> > >> > Note that the MRS interface will still return the sanitized content >> > _only_. >> > >> > Signed-off-by: Qais Yousef >> > --- >> > >> > Example output. I was surprised that the 2nd field (bits[7:4]) is >> > printed out >> > although it's set as FTR_HIDDEN. >> > >> > # cat /sys/devices/system/cpu/cpu*/regs/identification/id_aa64pfr0 >> > 0x0000000000000011 >> > 0x0000000000000011 >> > 0x0000000000000011 >> > 0x0000000000000011 >> > 0x0000000000000011 >> > 0x0000000000000011 >> > >> > # echo 1 > /proc/sys/kernel/enable_asym_32bit >> > >> > # cat /sys/devices/system/cpu/cpu*/regs/identification/id_aa64pfr0 >> > 0x0000000000000011 >> > 0x0000000000000011 >> > 0x0000000000000012 >> > 0x0000000000000012 >> > 0x0000000000000011 >> > 0x0000000000000011 >> >> This looks like a terrible userspace interface. > > It's also not allowed, sorry. sysfs is "one value per file", which is > NOT what is happening at all. I *think* Qais got that part right, though it is hard to tell without knowing how many CPUs this system has (cpu/cpu* is ambiguous). M. -- Jazz is not dead. It just smells funny... _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel