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Received: from dhcp-077-249-017-003.chello.nl ([77.249.17.3] helo=worktop.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.94.2 #2 (Red Hat Linux)) id 1nzElj-00DR5R-4H; Thu, 09 Jun 2022 09:47:59 +0000 Received: by worktop.programming.kicks-ass.net (Postfix, from userid 1000) id 100CA981287; Thu, 9 Jun 2022 11:47:58 +0200 (CEST) Date: Thu, 9 Jun 2022 11:47:57 +0200 From: Peter Zijlstra To: Tony Lindgren Subject: Re: [PATCH 33/36] cpuidle,omap3: Use WFI for omap3_pm_idle() Message-ID: References: <20220608142723.103523089@infradead.org> <20220608144518.010587032@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Mailman-Approved-At: Fri, 10 Jun 2022 21:09:20 +1000 X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Juri Lelli , Rafael Wysocki , Linus Walleij , Ben Segall , Guo Ren , Pavel Machek , Alexander Gordeev , srivatsa@csail.mit.edu, linux-arch , Vincent Guittot , Huacai Chen , ACPI Devel Maling List , Andy Gross , Geert Uytterhoeven , NXP Linux Team , Catalin Marinas , xen-devel , Matt Turner , Christian Borntraeger , Michael Turquette , Sam Creasey , Petr Mladek , Linux PM list , Lai Jiangshan , Sascha Hauer , linux-um , Arnaldo Carvalho de Melo , Thomas Gleixner , linux-omap , Dietmar Eggemann , Richard Henderson , gregkh , Linux Kernel Mailing List , linux-perf-users@vger.kernel.org, Sergey Senozhatsky , Sven Schnelle , Jiri Olsa , Paul Mackerras , Mark Rutland , "open list:IA64 \(Itanium\) PLATFORM" , Dave Hansen , "open list:DRM DRIVER FOR QEMU'S CIRRUS DEVICE" , James Bottomley , Max Filippov , Thierry Reding , Xuerui Wang , quic_neeraju@quicinc.com, linux-s390 , vschneid@redhat.com, John Ogn ess , Yoshinori Sato , Linux-sh list , Will Deacon , Helge Deller , Daniel Lezcano , Jonathan Hunter , Mathieu Desnoyers , Frederic Weisbecker , Len Brown , "open list:TENSILICA XTENSA PORT \(xtensa\)" , Sascha Hauer , Vasily Gorbik , linux-arm-msm , alpha , linux-m68k , Stafford Horne , Linux ARM , Chris Zankel , Stephen Boyd , Dinh Nguyen , Daniel Bristot de Oliveira , Alexander Shishkin , lpieralisi@kernel.org, Rasmus Villemoes , Joel Fernandes , Fabio Estevam , Boris Ostrovsky , Kevin Hilman , linux-csky@vger.kernel.org, "open list:SYNOPSYS ARC ARCHITECTURE" , Mel Gorman , jacob.jun.pan@linux.intel.com, Arnd Bergmann , Hans Ulli Kroll , Vineet Gupta , linux-clk , Josh Triplett , Steven Rostedt , rcu@vger.kernel.org, Borislav Petkov , bcain@quicinc.com, Thomas Bogendoerfer , Parisc List , Sudeep Holla , Shawn Guo , David Miller , Rich Felker , Pv-drivers , amakhalov@vmware.com, Bjorn Andersson , "H. Peter Anvin" , sparclinux , "open list:QUALCOMM HEXAGON..." , linux-riscv , Anton Ivanov , Jonas Bonn , Yury Norov , Richard Weinberger , the arch/x86 maintainers , Russell King - ARM Linux , Ingo Molnar , Albert Ou , "Paul E. McKenney" , Heiko Carstens , Stefan Kristiansson , Openrisc , Paul Walmsley , "open list:TEGRA ARCHITECTURE SUPPORT" , Namhyung Kim , Andy Shevchenko , jpoimboe@kernel.org, Juergen Gross , Michal Simek , "open list:BROADCOM NVRAM DRIVER" , Palmer Dabbelt , Anup Patel , Ivan Kokshaysky , Johannes Berg , linuxppc-dev Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Thu, Jun 09, 2022 at 10:39:22AM +0300, Tony Lindgren wrote: > * Arnd Bergmann [220608 18:18]: > > On Wed, Jun 8, 2022 at 4:27 PM Peter Zijlstra wrote: > > > > > > arch_cpu_idle() is a very simple idle interface and exposes only a > > > single idle state and is expected to not require RCU and not do any > > > tracing/instrumentation. > > > > > > As such, omap_sram_idle() is not a valid implementation. Replace it > > > with the simple (shallow) omap3_do_wfi() call. Leaving the more > > > complicated idle states for the cpuidle driver. > > Agreed it makes sense to limit deeper idle states to cpuidle. Hopefully > there is some informative splat for attempting to use arch_cpu_ide() > for deeper idle states :) The arch_cpu_idle() interface doesn't allow one to express a desire for deeper states. I'm not sure how anyone could even attempt this. But given what OMAP needs to go deeper, this would involve things that require RCU, combine that with the follow up patches that rip out all the trace_.*_rcuidle() hackery from the power and clock domain code, PROVE_RCU should scream if anybody were to attempt it.