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Mon, 20 Jan 2020 11:56:34 +0000 MIME-Version: 1.0 Date: Mon, 20 Jan 2020 12:56:34 +0100 From: Marc Zyngier To: Vladimir Murzin Subject: Re: [PATCH] ARM: virt: Relax arch timer version check during early boot In-Reply-To: <38a43fed-1c7a-69ea-3662-e17f13ca74d6@arm.com> References: <1579097798-106243-1-git-send-email-vladimir.murzin@arm.com> <38a43fed-1c7a-69ea-3662-e17f13ca74d6@arm.com> Message-ID: <55fbdb33fc3e107385c12def941aa934@kernel.org> X-Sender: maz@kernel.org User-Agent: Roundcube Webmail/1.3.8 X-SA-Exim-Connect-IP: 51.254.78.96 X-SA-Exim-Rcpt-To: vladimir.murzin@arm.com, linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu 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-20200120_035637_136021_9CAB59F2 X-CRM114-Status: GOOD ( 13.14 ) 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: 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+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 2020-01-20 12:34, Vladimir Murzin wrote: > Hi Marc, > > On 1/20/20 11:14 AM, Marc Zyngier wrote: >> Hi Vladimir, >> >> On 2020-01-20 11:46, Vladimir Murzin wrote: >>> + Marc >>> + kvmarm@lists.cs.columbia.edu >>> >>> On 1/15/20 2:16 PM, Vladimir Murzin wrote: >>>> Updates to the Generic Timer architecture allow ID_PFR1.GenTimer to >>>> have values other than 0 or 1. At the moment, Linux is quite strict >>>> in >>>> the way it handles this field at early boot and will not configure >>>> arch timer if it doesn't find the value 1. >>>> >>>> Since here use ubfx for arch timer version extraction (hyb-stub >>>> build >>>> with -march=armv7-a, so it is safe) >>>> >>>> To help backports (even though the code was correct at the time of >>>> writing) >>>> Fixes: 8ec58be9f3ff ("ARM: virt: arch_timers: enable access to >>>> physical timers") >>>> Signed-off-by: Vladimir Murzin >> >> I'm not opposed to such a change, but it'd be good to document what >> other values >> are expected here, as the current (Rev E_a) ARM ARM only mentions >> values 0 and 1. > > That true, ARM ARM doesn't mention it yet. OTOH, should we really care > about exact values as soon it stays compatible? That's for you to say, really. But given that you hint at some changes, it'd be good to have at least a short sentence explaining that, for example, "upcoming revisions of the architecture will allow different ID_PFR1.GenTimer values while preserving backward compatibility". Other than that, feel free to add my Acked-by: Marc Zyngier 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