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Tue, 14 Jul 2020 12:34:16 +0100 MIME-Version: 1.0 Date: Tue, 14 Jul 2020 12:34:15 +0100 From: Marc Zyngier To: zhukeqian Subject: Re: [Question] About scaling factor of Enhanced Counter Virtualization In-Reply-To: References: User-Agent: Roundcube Webmail/1.4.5 Message-ID: X-Sender: maz@kernel.org X-SA-Exim-Connect-IP: 51.254.78.96 X-SA-Exim-Rcpt-To: zhukeqian1@huawei.com, linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, james.morse@arm.com, catalin.marinas@arm.com, will@kernel.org, suzuki.poulose@arm.com, yebiaoxiang@huawei.com, xiexiangyou@huawei.com, wanghaibin.wang@huawei.com 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-20200714_073418_291224_502D6D76 X-CRM114-Status: GOOD ( 13.81 ) 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: "Suzuki K, Poulose" , Catalin Marinas , xiexiangyou@huawei.com, yebiaoxiang@huawei.com, James Morse , wanghaibin.wang@huawei.com, Will Deacon , kvmarm@lists.cs.columbia.edu, 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 Hi Keqian, On 2020-07-14 03:20, zhukeqian wrote: > Hi all, > > We are studying Enhanced Counter Virtualization (introduced by ARMv8.6 > extension), and here is a question > raised by Biaoxiang Ye : > > Described in the ARMv8.6 Extension Specification: > Note: the scaling factor CNTSCALE is designed as a 2.62 bit fixed > point number, so permitting a scaling up by > (nearly) a factor 4. The scaling factor CNTISCALE is signed as an 8.56 > number for the scaling of the values > written into the timers for comparison with the actual count. This > implies that the greatest scaling down of the > counter supported in (nearly) a factor of *512*. > > We think the number "512" should be "256" (2^8), or do we miss > something? This register doesn't seem to be described in ARM DDI 0487F.b, which is the official documentation and does contain the ARMv8.6 material, including ARMv8.6-ECV. Either you are looking at confidential information (and nobody can answer you in public), or obsolete information (and nobody knows what this is about). In any case, this is most probably a question for ARM's support team, and not the kernel mailing lists. Thanks, 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