| Message ID | 20220608144518.010587032@infradead.org (mailing list archive) |
|---|---|
| State | Handled Elsewhere, archived |
| Headers | show |
| Series | cpuidle,rcu: Cleanup the mess | expand |
On Wed, Jun 8, 2022 at 4:27 PM Peter Zijlstra <peterz@infradead.org> 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. > > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> I see similar code in omap2: omap2_pm_idle() -> omap2_enter_full_retention() -> omap2_sram_suspend() Is that code path safe to use without RCU or does it need a similar change? Arnd
* Arnd Bergmann <arnd@arndb.de> [220608 18:18]: > On Wed, Jun 8, 2022 at 4:27 PM Peter Zijlstra <peterz@infradead.org> 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 :) > I see similar code in omap2: > > omap2_pm_idle() > -> omap2_enter_full_retention() > -> omap2_sram_suspend() > > Is that code path safe to use without RCU or does it need a similar change? Seems like a similar change should be done for omap2. Then anybody who cares to implement a minimal cpuidle support can do so. Regards, Tony
On Wed, Jun 08, 2022 at 06:28:33PM +0200, Arnd Bergmann wrote: > On Wed, Jun 8, 2022 at 4:27 PM Peter Zijlstra <peterz@infradead.org> 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. > > > > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> > > I see similar code in omap2: > > omap2_pm_idle() > -> omap2_enter_full_retention() > -> omap2_sram_suspend() > > Is that code path safe to use without RCU or does it need a similar change? It needs a similar change, clearly I was running on fumes to not have found that when grepping around the omap code :/
On Thu, Jun 09, 2022 at 10:39:22AM +0300, Tony Lindgren wrote: > * Arnd Bergmann <arnd@arndb.de> [220608 18:18]: > > On Wed, Jun 8, 2022 at 4:27 PM Peter Zijlstra <peterz@infradead.org> 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.
* Peter Zijlstra <peterz@infradead.org> [220608 14:52]: > 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. Acked-by: Tony Lindgren <tony@atomide.com>
--- a/arch/arm/mach-omap2/pm34xx.c +++ b/arch/arm/mach-omap2/pm34xx.c @@ -294,7 +294,7 @@ static void omap3_pm_idle(void) if (omap_irq_pending()) return; - omap_sram_idle(); + omap3_do_wfi(); } #ifdef CONFIG_SUSPEND
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. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> --- arch/arm/mach-omap2/pm34xx.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)