| Message ID | 1442369095-1094-2-git-send-email-yingjoe.chen@mediatek.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On 16/09/15 03:04, Yingjoe Chen wrote: > From: Daniel Kurtz <djkurtz@chromium.org> > > Add device node to enable GPT timer. This timer will be > used as sched clock source. > Interesting any known issues with or advantage over the arch timers to prefer it as sched clock source. I see even arch timers are present in DT, hence the question. Or is it just a incorrect commit log ? How does this get selected as sched clock source ? I don't see sched_clock_register in mtk_timer.c To be clear, I am not against adding this timer support, but just want to know is it preferred for sched clock source ? if yes why ? better resolution ? > Change-Id: Idc4e3f0ee80b5c36cae6f0f2328f94aafcca1253 ^ Should be dropped > Signed-off-by: Daniel Kurtz <djkurtz@chromium.org> > Signed-off-by: Eddie Huang <eddie.huang@mediatek.com> > Signed-off-by: Yingjoe Chen <yingjoe.chen@mediatek.com> > --- > arch/arm64/boot/dts/mediatek/mt8173.dtsi | 9 +++++++++ > 1 file changed, 9 insertions(+) > > diff --git a/arch/arm64/boot/dts/mediatek/mt8173.dtsi b/arch/arm64/boot/dts/mediatek/mt8173.dtsi > index d18ee42..d763803 100644 > --- a/arch/arm64/boot/dts/mediatek/mt8173.dtsi > +++ b/arch/arm64/boot/dts/mediatek/mt8173.dtsi > @@ -238,6 +238,15 @@ > reg = <0 0x10007000 0 0x100>; > }; > > + timer: timer@10008000 { > + compatible = "mediatek,mt8173-timer", Missing documentation ? I am referring upstream and it might be in some patches already queued perhaps ? Regards, Sudeep
On Thu, 2015-09-17 at 14:51 +0100, Sudeep Holla wrote: > > On 16/09/15 03:04, Yingjoe Chen wrote: > > From: Daniel Kurtz <djkurtz@chromium.org> > > > > Add device node to enable GPT timer. This timer will be > > used as sched clock source. > > > > Interesting any known issues with or advantage over the arch timers > to prefer it as sched clock source. I see even arch timers are present > in DT, hence the question. Or is it just a incorrect commit log ? > > How does this get selected as sched clock source ? I don't see > sched_clock_register in mtk_timer.c > > To be clear, I am not against adding this timer support, but just want > to know is it preferred for sched clock source ? if yes why ? better > resolution ? Hi Sudeep, Thanks for your review. I hit the send too soon and missed cover letter, please see: http://lists.infradead.org/pipermail/linux-mediatek/2015-September/002303.html The main reason to use GPT as sched clock is it won't stop during idle. > > Change-Id: Idc4e3f0ee80b5c36cae6f0f2328f94aafcca1253 > > ^ Should be dropped > > > Signed-off-by: Daniel Kurtz <djkurtz@chromium.org> > > Signed-off-by: Eddie Huang <eddie.huang@mediatek.com> > > Signed-off-by: Yingjoe Chen <yingjoe.chen@mediatek.com> > > --- > > arch/arm64/boot/dts/mediatek/mt8173.dtsi | 9 +++++++++ > > 1 file changed, 9 insertions(+) > > > > diff --git a/arch/arm64/boot/dts/mediatek/mt8173.dtsi b/arch/arm64/boot/dts/mediatek/mt8173.dtsi > > index d18ee42..d763803 100644 > > --- a/arch/arm64/boot/dts/mediatek/mt8173.dtsi > > +++ b/arch/arm64/boot/dts/mediatek/mt8173.dtsi > > @@ -238,6 +238,15 @@ > > reg = <0 0x10007000 0 0x100>; > > }; > > > > + timer: timer@10008000 { > > + compatible = "mediatek,mt8173-timer", > > Missing documentation ? I am referring upstream and it might be in some > patches already queued perhaps ? This is documented in Documentation/devicetree/bindings/timer/mediatek,mtk-timer.txt. Do you mean I should add "mediatek,mt8173-timer" to that file? Joe.C
On 17/09/15 15:56, Yingjoe Chen wrote: > On Thu, 2015-09-17 at 14:51 +0100, Sudeep Holla wrote: >> >> On 16/09/15 03:04, Yingjoe Chen wrote: >>> From: Daniel Kurtz <djkurtz@chromium.org> >>> >>> Add device node to enable GPT timer. This timer will be >>> used as sched clock source. >>> >> >> Interesting any known issues with or advantage over the arch timers >> to prefer it as sched clock source. I see even arch timers are present >> in DT, hence the question. Or is it just a incorrect commit log ? >> >> How does this get selected as sched clock source ? I don't see >> sched_clock_register in mtk_timer.c >> >> To be clear, I am not against adding this timer support, but just want >> to know is it preferred for sched clock source ? if yes why ? better >> resolution ? > > Hi Sudeep, > > Thanks for your review. > > I hit the send too soon and missed cover letter, please see: > http://lists.infradead.org/pipermail/linux-mediatek/2015-September/002303.html > OK > The main reason to use GPT as sched clock is it won't stop during idle. > > I think your are confusing the system counter with arch timers. System counter is always-on, but the arch timers(logic implementing timers comparators) might not be off when the processor is powered down. I think you need this timer and are using it for low power idle states in which case you will use this as a clock event and not clock source. It will be used as a hardware broadcast event source. There's no call to sched_clock_register in mtk_timer.c, so it can't be the sched clock, so you need to fix the commit log. [...] >>> diff --git a/arch/arm64/boot/dts/mediatek/mt8173.dtsi b/arch/arm64/boot/dts/mediatek/mt8173.dtsi >>> index d18ee42..d763803 100644 >>> --- a/arch/arm64/boot/dts/mediatek/mt8173.dtsi >>> +++ b/arch/arm64/boot/dts/mediatek/mt8173.dtsi >>> @@ -238,6 +238,15 @@ >>> reg = <0 0x10007000 0 0x100>; >>> }; >>> >>> + timer: timer@10008000 { >>> + compatible = "mediatek,mt8173-timer", >> >> Missing documentation ? I am referring upstream and it might be in some >> patches already queued perhaps ? > > This is documented in > Documentation/devicetree/bindings/timer/mediatek,mtk-timer.txt. > Do you mean I should add "mediatek,mt8173-timer" to that file? > Yes Regards, Sudeep
On Thu, Sep 17, 2015 at 03:56:56PM +0100, Yingjoe Chen wrote: > On Thu, 2015-09-17 at 14:51 +0100, Sudeep Holla wrote: > > > > On 16/09/15 03:04, Yingjoe Chen wrote: > > > From: Daniel Kurtz <djkurtz@chromium.org> > > > > > > Add device node to enable GPT timer. This timer will be > > > used as sched clock source. > > > > > > > Interesting any known issues with or advantage over the arch timers > > to prefer it as sched clock source. I see even arch timers are present > > in DT, hence the question. Or is it just a incorrect commit log ? > > > > How does this get selected as sched clock source ? I don't see > > sched_clock_register in mtk_timer.c > > > > To be clear, I am not against adding this timer support, but just want > > to know is it preferred for sched clock source ? if yes why ? better > > resolution ? > > Hi Sudeep, > > Thanks for your review. > > I hit the send too soon and missed cover letter, please see: > http://lists.infradead.org/pipermail/linux-mediatek/2015-September/002303.html > > The main reason to use GPT as sched clock is it won't stop during idle. You don't mean sched clock, you just mean a clock_event_device. A sched_clock is a high-precision clocksource that is read from (which by definition requires the CPUs to be non-idle). It doesn't have anything to do with interrupts and therefore cannot wake devices from idle. While the clock_event_device for the generic timer can't necessarily wake CPUs from idle. The generic timer system counter counts even if CPUs are idle, so the generic timer is fine as a sched_clock. Thanks, Mark.
On Thu, 2015-09-17 at 17:13 +0100, Sudeep Holla wrote: > > On 17/09/15 15:56, Yingjoe Chen wrote: > > On Thu, 2015-09-17 at 14:51 +0100, Sudeep Holla wrote: > >> > >> On 16/09/15 03:04, Yingjoe Chen wrote: > >>> From: Daniel Kurtz <djkurtz@chromium.org> > >>> > >>> Add device node to enable GPT timer. This timer will be > >>> used as sched clock source. > >>> > >> > >> Interesting any known issues with or advantage over the arch timers > >> to prefer it as sched clock source. I see even arch timers are present > >> in DT, hence the question. Or is it just a incorrect commit log ? > >> > >> How does this get selected as sched clock source ? I don't see > >> sched_clock_register in mtk_timer.c > >> > >> To be clear, I am not against adding this timer support, but just want > >> to know is it preferred for sched clock source ? if yes why ? better > >> resolution ? > > > > Hi Sudeep, > > > > Thanks for your review. > > > > I hit the send too soon and missed cover letter, please see: > > http://lists.infradead.org/pipermail/linux-mediatek/2015-September/002303.html > > > > OK > > > The main reason to use GPT as sched clock is it won't stop during idle. > > > > > > I think your are confusing the system counter with arch timers. System > counter is always-on, but the arch timers(logic implementing timers > comparators) might not be off when the processor is powered down. > > I think you need this timer and are using it for low power idle states > in which case you will use this as a clock event and not clock source. > It will be used as a hardware broadcast event source. > > There's no call to sched_clock_register in mtk_timer.c, so it can't be > the sched clock, so you need to fix the commit log. Hi Sudeep, Sorry for late reply. For sched_clock_register, please see http://lists.infradead.org/pipermail/linux-mediatek/2015-July/001547.html which was accepted in https://git.linaro.org/people/daniel.lezcano/linux.git/shortlog/refs/heads/clockevents/4.4 You are right it is also used as clock event. I think we don't need to mention those detail in commit message, so I'll change to just: "Add device node to enable GPT timer." > > [...] > > >>> diff --git a/arch/arm64/boot/dts/mediatek/mt8173.dtsi b/arch/arm64/boot/dts/mediatek/mt8173.dtsi > >>> index d18ee42..d763803 100644 > >>> --- a/arch/arm64/boot/dts/mediatek/mt8173.dtsi > >>> +++ b/arch/arm64/boot/dts/mediatek/mt8173.dtsi > >>> @@ -238,6 +238,15 @@ > >>> reg = <0 0x10007000 0 0x100>; > >>> }; > >>> > >>> + timer: timer@10008000 { > >>> + compatible = "mediatek,mt8173-timer", > >> > >> Missing documentation ? I am referring upstream and it might be in some > >> patches already queued perhaps ? > > > > This is documented in > > Documentation/devicetree/bindings/timer/mediatek,mtk-timer.txt. > > Do you mean I should add "mediatek,mt8173-timer" to that file? > > > > Yes Will do in next round. Thanks Joe.C
On Thu, 2015-09-17 at 17:41 +0100, Mark Rutland wrote: > On Thu, Sep 17, 2015 at 03:56:56PM +0100, Yingjoe Chen wrote: > > On Thu, 2015-09-17 at 14:51 +0100, Sudeep Holla wrote: > > > > > > On 16/09/15 03:04, Yingjoe Chen wrote: > > > > From: Daniel Kurtz <djkurtz@chromium.org> > > > > > > > > Add device node to enable GPT timer. This timer will be > > > > used as sched clock source. > > > > > > > > > > Interesting any known issues with or advantage over the arch timers > > > to prefer it as sched clock source. I see even arch timers are present > > > in DT, hence the question. Or is it just a incorrect commit log ? > > > > > > How does this get selected as sched clock source ? I don't see > > > sched_clock_register in mtk_timer.c > > > > > > To be clear, I am not against adding this timer support, but just want > > > to know is it preferred for sched clock source ? if yes why ? better > > > resolution ? > > > > Hi Sudeep, > > > > Thanks for your review. > > > > I hit the send too soon and missed cover letter, please see: > > http://lists.infradead.org/pipermail/linux-mediatek/2015-September/002303.html > > > > The main reason to use GPT as sched clock is it won't stop during idle. > > You don't mean sched clock, you just mean a clock_event_device. > > A sched_clock is a high-precision clocksource that is read from (which > by definition requires the CPUs to be non-idle). It doesn't have > anything to do with interrupts and therefore cannot wake devices from > idle. > > While the clock_event_device for the generic timer can't necessarily > wake CPUs from idle. The generic timer system counter counts even if > CPUs are idle, so the generic timer is fine as a sched_clock. Hi, Mark, Thanks for your info and sorry for late reply. I notice ARM ARM said the arch timer shouldn't stop when idle, but unfortunately that not true for mt8173. The last CPU enter idle can choose to enter deep idle mode and the counter value would be lost. Our firmware backup/recover the counter so it looks like it is stopped. We will change the firmware to add missing count when back from deep idle to make it looks like the counter never stop. Joe.C
On 01/10/15 15:33, Yingjoe Chen wrote: > On Thu, 2015-09-17 at 17:13 +0100, Sudeep Holla wrote: >> [...] >> >> I think your are confusing the system counter with arch timers. System >> counter is always-on, but the arch timers(logic implementing timers >> comparators) might not be off when the processor is powered down. >> >> I think you need this timer and are using it for low power idle states >> in which case you will use this as a clock event and not clock source. >> It will be used as a hardware broadcast event source. >> >> There's no call to sched_clock_register in mtk_timer.c, so it can't be >> the sched clock, so you need to fix the commit log. > > Hi Sudeep, > > Sorry for late reply. > > For sched_clock_register, please see > http://lists.infradead.org/pipermail/linux-mediatek/2015-July/001547.html > which was accepted in > https://git.linaro.org/people/daniel.lezcano/linux.git/shortlog/refs/heads/clockevents/4.4 > The commit message makes no sense to me. The counters should continue to work as long as they are in always-on domain. Only timers are lost when you enter deeper idle states. So I agree with using MTK timer as broadcast timer/eventsource. You still didn't answer what's the need to use MTK timer as sched clocksource ? Regards, Sudeep
On Thu, 2015-10-01 at 16:32 +0100, Sudeep Holla wrote: > > On 01/10/15 15:33, Yingjoe Chen wrote: > > On Thu, 2015-09-17 at 17:13 +0100, Sudeep Holla wrote: > >> > > [...] > > >> > >> I think your are confusing the system counter with arch timers. System > >> counter is always-on, but the arch timers(logic implementing timers > >> comparators) might not be off when the processor is powered down. > >> > >> I think you need this timer and are using it for low power idle states > >> in which case you will use this as a clock event and not clock source. > >> It will be used as a hardware broadcast event source. > >> > >> There's no call to sched_clock_register in mtk_timer.c, so it can't be > >> the sched clock, so you need to fix the commit log. > > > > Hi Sudeep, > > > > Sorry for late reply. > > > > For sched_clock_register, please see > > http://lists.infradead.org/pipermail/linux-mediatek/2015-July/001547.html > > which was accepted in > > https://git.linaro.org/people/daniel.lezcano/linux.git/shortlog/refs/heads/clockevents/4.4 > > > > The commit message makes no sense to me. The counters should continue to > work as long as they are in always-on domain. Only timers are lost > when you enter deeper idle states. So I agree with using MTK timer as > broadcast timer/eventsource. You still didn't answer what's the need > to use MTK timer as sched clocksource ? Hi, Sudeep, ARM ARM said the counter should be in always-on domain, but unfortunately that not true for mt8173. The last CPU enter idle can choose to enter deep idle mode and the counter value would be lost. Our firmware backup/recover the counter so it looks like it is stopped. That's why I thought we need to use it as sched clocksource. On mt8173, we will fix the firmware to add missing counts, so it will looks like the counter keep counting. But other mediatek platform have similar issue, and the 2 counter have same resolution, so I still want to keep using GPT as sched clocksource. Joe.C
diff --git a/arch/arm64/boot/dts/mediatek/mt8173.dtsi b/arch/arm64/boot/dts/mediatek/mt8173.dtsi index d18ee42..d763803 100644 --- a/arch/arm64/boot/dts/mediatek/mt8173.dtsi +++ b/arch/arm64/boot/dts/mediatek/mt8173.dtsi @@ -238,6 +238,15 @@ reg = <0 0x10007000 0 0x100>; }; + timer: timer@10008000 { + compatible = "mediatek,mt8173-timer", + "mediatek,mt6577-timer"; + reg = <0 0x10008000 0 0x1000>; + interrupts = <GIC_SPI 144 IRQ_TYPE_LEVEL_LOW>; + clocks = <&infracfg CLK_INFRA_CLK_13M>, + <&topckgen CLK_TOP_RTC_SEL>; + }; + pwrap: pwrap@1000d000 { compatible = "mediatek,mt8173-pwrap"; reg = <0 0x1000d000 0 0x1000>;