On 2018-01-09 15:04, Lucas Stach wrote: > Am Dienstag, den 09.01.2018, 14:37 +0100 schrieb Stefan Agner: >> On 2018-01-09 11:13, Lucas Stach wrote: >> > Am Dienstag, den 09.01.2018, 09:25 +0000 schrieb Anson Huang: >> > > >> > > Best Regards! >> > > Anson Huang >> > > >> > > >> > > > -----Original Message----- >> > > > From: Dong Aisheng [mailto:dongas86@xxxxxxxxx] >> > > > Sent: 2018-01-09 5:23 PM >> > > > To: Stefan Agner <stefan@xxxxxxxx> >> > > > Cc: shawnguo@xxxxxxxxxx; kernel@xxxxxxxxxxxxxx; Fabio Estevam >> > > > <fabio.estevam@xxxxxxx>; robh+dt@xxxxxxxxxx; mark.rutland@arm.c >> > > > om; >> > > > linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; devicetree@xxxxxxxxxxxxxx >> > > > g; >> > > > linux- >> > > > kernel@xxxxxxxxxxxxxxx; Anson Huang <anson.huang@xxxxxxx>; dl- >> > > > linux-imx >> > > > <linux-imx@xxxxxxx> >> > > > Subject: Re: [PATCH 1/7] ARM: imx: add timer stop flag to ARM >> > > > power >> > > > off state >> > > > >> > > > On Tue, Jan 02, 2018 at 05:42:17PM +0100, Stefan Agner wrote: >> > > > > When the CPU is in ARM power off state the ARM architected >> > > > > timers >> > > > > are >> > > > > stopped. The flag is already present in the higher power WAIT >> > > > > mode. >> > > > > >> > > > > This allows to use the ARM generic timer on i.MX 6UL/6ULL >> > > > > SoC. >> > > > > Without the flag the kernel freezes when the timer enters the >> > > > > first >> > > > > time ARM power off mode. >> > > > > >> > > > > Cc: Anson Huang <anson.huang@xxxxxxx> >> > > > > Signed-off-by: Stefan Agner <stefan@xxxxxxxx> >> > > > >> > > > It seems ok at my side. >> > > > Did you meet the real issue? If yes, how to reproduce? >> > > > >> > > > Both mx6sx and mx6ul are using GPT which do not need that flag, >> > > > suppose we >> > > > should remove it, right? >> > > > Anson can help confirm it. >> > > >> > > For UP system like i.MX6SX, we do NOT enable "cortex-a9-twd- >> > > timer", >> > > so local >> > > timer is NOT used, GPT is used instead, GPT's clock is NOT >> > > disabled >> > > when cpuidle, >> > > so I think we should remove all these Timer stop flag for 6SX >> > > CPUIDLE. >> > >> > It's correct to set the flag even on UP systems, as the flag means >> > the >> > CPU _local_ timer is stopped in this sleep mode. Also there are >> > systems >> > out there which are using the TWD on UP, as it operates at a higher >> > frequency leading to better wakeup granularity. >> >> Documentation/devicetree/bindings/arm/twd.txt states that TWD >> provides >> "per-cpu local timer". But as far as I can see TWD still uses SPI >> interrupts, routed through GIC, so is this the differentiation? > > Maybe what I wrote wasn't entirely clear. I completely agree with this > patch. > > The TWD on Cortex-A9 is a CPU local timer, same as the architected > timer in later cores. It doesn't provide all the benefits of the > architected timer (the clock frequency varies with CPU core clock and > it's not virt capable), but some systems still prefer it over the i.MX > GPT, as it provides much better wakeup granularity. > > So annotating the CPU idle states with the timer stop flag is the right > thing to do. This flag has nothing to with the usage of GPT or TWD on a > specific system. Can I take that as an Acked-by? -- Stefan -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
