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Received: from shell.armlinux.org.uk ([fd8f:7570:feb6:1:5054:ff:fe00:4ec]:39048) by pandora.armlinux.org.uk with esmtpsa (TLS1.3:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1l7cB8-0006SM-2m; Thu, 04 Feb 2021 10:48:02 +0000 Received: from linux by shell.armlinux.org.uk with local (Exim 4.92) (envelope-from ) id 1l7cAN-000564-1Y; Thu, 04 Feb 2021 10:47:15 +0000 Date: Thu, 4 Feb 2021 10:47:15 +0000 From: Russell King - ARM Linux admin To: Ard Biesheuvel Subject: Re: next/master bisection: baseline.login on rk3288-rock2-square Message-ID: <20210204104714.GU1463@shell.armlinux.org.uk> References: <601b773a.1c69fb81.9f381.a32a@mx.google.com> <6c65bcef-d4e7-25fa-43cf-2c435bb61bb9@collabora.com> <20210204100601.GT1463@shell.armlinux.org.uk> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210204_054805_334980_CD3F9AA5 X-CRM114-Status: GOOD ( 20.17 ) 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: "kernelci-results@groups.io" , Geert Uytterhoeven , Nicolas Pitre , Guillaume Tucker , Linus Walleij , Linux Kernel Mailing List , Linux ARM Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Thu, Feb 04, 2021 at 11:27:16AM +0100, Ard Biesheuvel wrote: > Hi Russell, > > If Guillaume is willing to do the experiment, and it fixes the issue, > it proves that rk3288 is relying on the flush before the MMU is > disabled, and so in that case, the fix is trivial, and we can just > apply it. > > If the experiment fails (which would mean rk3288 does not tolerate the > cache maintenance being performed after cache off), it is going to be > hairy, and so it will definitely take more time. > > So in the latter case (or if Guillaume does not get back to us), I > think reverting my queued fix is the only sane option. But in that > case, may I suggest that we queue the revert of the original by-VA > change for v5.12 so it gets lots of coverage in -next, and allows us > an opportunity to come up with a proper fix in the same timeframe, and > backport the revert and the subsequent fix as a pair? Otherwise, we'll > end up in the situation where v5.10.x until today has by-va, v5.10.x-y > has set/way, and v5.10y+ has by-va again. (I don't think we care about > anything before that, given that v5.4 predates any of this) I'm suggesting dropping your fix (9052/1) and reverting "ARM: decompressor: switch to by-VA cache maintenance for v7 cores" which gets us to a point where _both_ regressions are fixed. I'm of the opinion that the by-VA patch was incorrect when it was merged (it caused a regression), and it's only a performance improvement. Our attempts so far to fix it are just causing other regressions. So, I think it is reasonable to revert both back to a known good point which has worked over a decade. If doing so causes regressions (which I think is unlikely), then that would be unfortunate but alas is a price that's worth paying to get back to a known good point - since then we're not stacking regression fixes on top of other regression fixes. -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last! _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel