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[PATCH 2/2] powernv:idle:Implement lite variant of power_enter_stop

Started by"Gautham R. Shenoy" <ego@linux.vnet.ibm.com>
First post2016-09-16 11:50 +0200
Last post2016-09-23 15:50 +0200
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  [PATCH 2/2] powernv:idle:Implement lite variant of power_enter_stop "Gautham R. Shenoy" <ego@linux.vnet.ibm.com> - 2016-09-16 11:50 +0200
    Re: [PATCH 2/2] powernv:idle:Implement lite variant of  power_enter_stop Balbir Singh <bsingharora@gmail.com> - 2016-09-20 08:00 +0200
      Re: [PATCH 2/2] powernv:idle:Implement lite variant of  power_enter_stop Gautham R Shenoy <ego@linux.vnet.ibm.com> - 2016-09-20 10:40 +0200
    Re: [PATCH 2/2] powernv:idle:Implement lite variant of power_enter_stop Michael Ellerman <mpe@ellerman.id.au> - 2016-09-23 13:10 +0200
      Re: [PATCH 2/2] powernv:idle:Implement lite variant of  power_enter_stop Gautham R Shenoy <ego@linux.vnet.ibm.com> - 2016-09-23 15:50 +0200

#1484846 — [PATCH 2/2] powernv:idle:Implement lite variant of power_enter_stop

From"Gautham R. Shenoy" <ego@linux.vnet.ibm.com>
Date2016-09-16 11:50 +0200
Subject[PATCH 2/2] powernv:idle:Implement lite variant of power_enter_stop
Message-ID<shXWp-2T3-11@gated-at.bofh.it>
From: "Gautham R. Shenoy" <ego@linux.vnet.ibm.com>

This patch adds a function named power_enter_stop_lite() that can
execute a stop instruction when ESL and EC bits are set to zero in the
PSSCR.  The function handles the wake-up from idle at the instruction
immediately after the stop instruction.

If the flag OPAL_PM_WAKEUP_AT_NEXT_INST[1] is set in the device tree
for a stop state, then use the lite variant for that particular stop
state.

[1] : The corresponding patch in skiboot that defines
      OPAL_PM_WAKEUP_AT_NEXT_INST and enables it in the device tree
      can be found here:
      https://lists.ozlabs.org/pipermail/skiboot/2016-September/004805.html

Signed-off-by: Gautham R. Shenoy <ego@linux.vnet.ibm.com>
---
 arch/powerpc/include/asm/opal-api.h   |  1 +
 arch/powerpc/include/asm/processor.h  |  3 ++-
 arch/powerpc/kernel/idle_book3s.S     | 28 +++++++++++++++++++++++++---
 arch/powerpc/platforms/powernv/idle.c | 17 ++++++++++++++---
 arch/powerpc/platforms/powernv/smp.c  |  2 +-
 drivers/cpuidle/cpuidle-powernv.c     | 24 ++++++++++++++++++++++--
 6 files changed, 65 insertions(+), 10 deletions(-)

diff --git a/arch/powerpc/include/asm/opal-api.h b/arch/powerpc/include/asm/opal-api.h
index 0e2e57b..6e5741e 100644
--- a/arch/powerpc/include/asm/opal-api.h
+++ b/arch/powerpc/include/asm/opal-api.h
@@ -179,6 +179,7 @@
 #define OPAL_PM_TIMEBASE_STOP		0x00000002
 #define OPAL_PM_LOSE_HYP_CONTEXT	0x00002000
 #define OPAL_PM_LOSE_FULL_CONTEXT	0x00004000
+#define OPAL_PM_WAKEUP_AT_NEXT_INST	0x00008000
 #define OPAL_PM_NAP_ENABLED		0x00010000
 #define OPAL_PM_SLEEP_ENABLED		0x00020000
 #define OPAL_PM_WINKLE_ENABLED		0x00040000
diff --git a/arch/powerpc/include/asm/processor.h b/arch/powerpc/include/asm/processor.h
index 68e3bf5..e0549a0 100644
--- a/arch/powerpc/include/asm/processor.h
+++ b/arch/powerpc/include/asm/processor.h
@@ -460,7 +460,8 @@ extern int powersave_nap;	/* set if nap mode can be used in idle loop */
 extern unsigned long power7_nap(int check_irq);
 extern unsigned long power7_sleep(void);
 extern unsigned long power7_winkle(void);
-extern unsigned long power9_idle_stop(unsigned long stop_level);
+extern unsigned long power9_idle_stop(unsigned long stop_level,
+				unsigned long exec_lite);
 
 extern void flush_instruction_cache(void);
 extern void hard_reset_now(void);
diff --git a/arch/powerpc/kernel/idle_book3s.S b/arch/powerpc/kernel/idle_book3s.S
index 32d666b..47ee106 100644
--- a/arch/powerpc/kernel/idle_book3s.S
+++ b/arch/powerpc/kernel/idle_book3s.S
@@ -43,6 +43,8 @@
 #define PSSCR_HV_TEMPLATE	PSSCR_ESL | PSSCR_EC | \
 				PSSCR_PSLL_MASK | PSSCR_TR_MASK | \
 				PSSCR_MTL_MASK
+#define PSSCR_HV_TEMPLATE_LITE	PSSCR_PSLL_MASK | PSSCR_TR_MASK | \
+				 PSSCR_MTL_MASK
 
 	.text
 
@@ -246,6 +248,20 @@ enter_winkle:
 
 	IDLE_STATE_ENTER_SEQ_NORET(PPC_WINKLE)
 
+
+/*
+ * power_enter_stop_lite : This will resume the wake up from
+ * idle at the subsequent instruction.
+ *
+ * Caller should set ESL=EC=0 in PSSCR before calling
+ * this function.
+ *
+ */
+power_enter_stop_lite:
+	IDLE_STATE_ENTER_SEQ(PPC_STOP)
+7:	li	r3,0  /* Since we didn't lose state, return 0 */
+	b 	pnv_wakeup_noloss
+
 /*
  * r3 - requested stop state
  */
@@ -333,13 +349,19 @@ ALT_FTR_SECTION_END_NESTED_IFSET(CPU_FTR_ARCH_207S, 66);		\
 
 /*
  * r3 - requested stop state
+ * r4 - Indicates if the lite variant with ESL=EC=0 should be executed.
  */
 _GLOBAL(power9_idle_stop)
-	LOAD_REG_IMMEDIATE(r4, PSSCR_HV_TEMPLATE)
-	or	r4,r4,r3
+	cmpdi	r4, 1
+	bne	4f
+	LOAD_REG_IMMEDIATE(r4, PSSCR_HV_TEMPLATE_LITE)
+	LOAD_REG_ADDR(r5,power_enter_stop_lite)
+	b 	5f
+4:	LOAD_REG_IMMEDIATE(r4, PSSCR_HV_TEMPLATE)
+	LOAD_REG_ADDR(r5,power_enter_stop)
+5:	or	r4,r4,r3
 	mtspr	SPRN_PSSCR, r4
 	li	r4, 1
-	LOAD_REG_ADDR(r5,power_enter_stop)
 	b	pnv_powersave_common
 	/* No return */
 /*
diff --git a/arch/powerpc/platforms/powernv/idle.c b/arch/powerpc/platforms/powernv/idle.c
index 479c256..c3d3fed 100644
--- a/arch/powerpc/platforms/powernv/idle.c
+++ b/arch/powerpc/platforms/powernv/idle.c
@@ -244,8 +244,15 @@ static DEVICE_ATTR(fastsleep_workaround_applyonce, 0600,
 static void power9_idle(void)
 {
 	/* Requesting stop state 0 */
-	power9_idle_stop(0);
+	power9_idle_stop(0, 0);
 }
+
+static void power9_idle_lite(void)
+{
+	/* Requesting stop state 0 with ESL=EC=0 */
+	power9_idle_stop(0, 1);
+}
+
 /*
  * First deep stop state. Used to figure out when to save/restore
  * hypervisor context.
@@ -414,8 +421,12 @@ static int __init pnv_init_idle_states(void)
 
 	if (supported_cpuidle_states & OPAL_PM_NAP_ENABLED)
 		ppc_md.power_save = power7_idle;
-	else if (supported_cpuidle_states & OPAL_PM_STOP_INST_FAST)
-		ppc_md.power_save = power9_idle;
+	else if (supported_cpuidle_states & OPAL_PM_STOP_INST_FAST) {
+		if (supported_cpuidle_states & OPAL_PM_WAKEUP_AT_NEXT_INST)
+			ppc_md.power_save = power9_idle_lite;
+		else
+			ppc_md.power_save = power9_idle;
+	}
 
 out:
 	return 0;
diff --git a/arch/powerpc/platforms/powernv/smp.c b/arch/powerpc/platforms/powernv/smp.c
index c789258..6587b96 100644
--- a/arch/powerpc/platforms/powernv/smp.c
+++ b/arch/powerpc/platforms/powernv/smp.c
@@ -183,7 +183,7 @@ static void pnv_smp_cpu_kill_self(void)
 		ppc64_runlatch_off();
 
 		if (cpu_has_feature(CPU_FTR_ARCH_300))
-			srr1 = power9_idle_stop(pnv_deepest_stop_state);
+			srr1 = power9_idle_stop(pnv_deepest_stop_state, 0);
 		else if (idle_states & OPAL_PM_WINKLE_ENABLED)
 			srr1 = power7_winkle();
 		else if ((idle_states & OPAL_PM_SLEEP_ENABLED) ||
diff --git a/drivers/cpuidle/cpuidle-powernv.c b/drivers/cpuidle/cpuidle-powernv.c
index f7ca891..7021ddf 100644
--- a/drivers/cpuidle/cpuidle-powernv.c
+++ b/drivers/cpuidle/cpuidle-powernv.c
@@ -102,7 +102,21 @@ static int stop_loop(struct cpuidle_device *dev,
 		     int index)
 {
 	ppc64_runlatch_off();
-	power9_idle_stop(stop_psscr_table[index]);
+	power9_idle_stop(stop_psscr_table[index], 0);
+	ppc64_runlatch_on();
+	return index;
+}
+
+/*
+ * This function calls stop instruction with
+ * ESL and EC bits set to 0.
+ */
+static int stop_lite_loop(struct cpuidle_device *dev,
+		     struct cpuidle_driver *drv,
+		     int index)
+{
+	ppc64_runlatch_off();
+	power9_idle_stop(stop_psscr_table[index], 1);
 	ppc64_runlatch_on();
 	return index;
 }
@@ -273,7 +287,13 @@ static int powernv_add_idle_states(void)
 				names[i], CPUIDLE_NAME_LEN);
 			powernv_states[nr_idle_states].flags = 0;
 
-			powernv_states[nr_idle_states].enter = stop_loop;
+			if (flags[i] & OPAL_PM_WAKEUP_AT_NEXT_INST) {
+				powernv_states[nr_idle_states].enter =
+					stop_lite_loop;
+			} else {
+				powernv_states[nr_idle_states].enter =
+					stop_loop;
+			}
 			stop_psscr_table[nr_idle_states] = psscr_val[i];
 		}
 
-- 
1.9.4

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#1487071 — Re: [PATCH 2/2] powernv:idle:Implement lite variant of power_enter_stop

FromBalbir Singh <bsingharora@gmail.com>
Date2016-09-20 08:00 +0200
SubjectRe: [PATCH 2/2] powernv:idle:Implement lite variant of power_enter_stop
Message-ID<sjmg1-7nQ-1@gated-at.bofh.it>
In reply to#1484846

On 16/09/16 19:47, Gautham R. Shenoy wrote:
> From: "Gautham R. Shenoy" <ego@linux.vnet.ibm.com>
> 
> This patch adds a function named power_enter_stop_lite() that can
> execute a stop instruction when ESL and EC bits are set to zero in the
> PSSCR.  The function handles the wake-up from idle at the instruction
> immediately after the stop instruction.
> 
> If the flag OPAL_PM_WAKEUP_AT_NEXT_INST[1] is set in the device tree
> for a stop state, then use the lite variant for that particular stop
> state.
> 
> [1] : The corresponding patch in skiboot that defines
>       OPAL_PM_WAKEUP_AT_NEXT_INST and enables it in the device tree
>       can be found here:
>       https://lists.ozlabs.org/pipermail/skiboot/2016-September/004805.html
> 
> Signed-off-by: Gautham R. Shenoy <ego@linux.vnet.ibm.com>
> ---
>  arch/powerpc/include/asm/opal-api.h   |  1 +
>  arch/powerpc/include/asm/processor.h  |  3 ++-
>  arch/powerpc/kernel/idle_book3s.S     | 28 +++++++++++++++++++++++++---
>  arch/powerpc/platforms/powernv/idle.c | 17 ++++++++++++++---
>  arch/powerpc/platforms/powernv/smp.c  |  2 +-
>  drivers/cpuidle/cpuidle-powernv.c     | 24 ++++++++++++++++++++++--
>  6 files changed, 65 insertions(+), 10 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/opal-api.h b/arch/powerpc/include/asm/opal-api.h
> index 0e2e57b..6e5741e 100644
> --- a/arch/powerpc/include/asm/opal-api.h
> +++ b/arch/powerpc/include/asm/opal-api.h
> @@ -179,6 +179,7 @@
>  #define OPAL_PM_TIMEBASE_STOP		0x00000002
>  #define OPAL_PM_LOSE_HYP_CONTEXT	0x00002000
>  #define OPAL_PM_LOSE_FULL_CONTEXT	0x00004000
> +#define OPAL_PM_WAKEUP_AT_NEXT_INST	0x00008000
>  #define OPAL_PM_NAP_ENABLED		0x00010000
>  #define OPAL_PM_SLEEP_ENABLED		0x00020000
>  #define OPAL_PM_WINKLE_ENABLED		0x00040000
> diff --git a/arch/powerpc/include/asm/processor.h b/arch/powerpc/include/asm/processor.h
> index 68e3bf5..e0549a0 100644
> --- a/arch/powerpc/include/asm/processor.h
> +++ b/arch/powerpc/include/asm/processor.h
> @@ -460,7 +460,8 @@ extern int powersave_nap;	/* set if nap mode can be used in idle loop */
>  extern unsigned long power7_nap(int check_irq);
>  extern unsigned long power7_sleep(void);
>  extern unsigned long power7_winkle(void);
> -extern unsigned long power9_idle_stop(unsigned long stop_level);
> +extern unsigned long power9_idle_stop(unsigned long stop_level,
> +				unsigned long exec_lite);
>  
>  extern void flush_instruction_cache(void);
>  extern void hard_reset_now(void);
> diff --git a/arch/powerpc/kernel/idle_book3s.S b/arch/powerpc/kernel/idle_book3s.S
> index 32d666b..47ee106 100644
> --- a/arch/powerpc/kernel/idle_book3s.S
> +++ b/arch/powerpc/kernel/idle_book3s.S
> @@ -43,6 +43,8 @@
>  #define PSSCR_HV_TEMPLATE	PSSCR_ESL | PSSCR_EC | \
>  				PSSCR_PSLL_MASK | PSSCR_TR_MASK | \
>  				PSSCR_MTL_MASK
> +#define PSSCR_HV_TEMPLATE_LITE	PSSCR_PSLL_MASK | PSSCR_TR_MASK | \
> +				 PSSCR_MTL_MASK
>  
>  	.text
>  
> @@ -246,6 +248,20 @@ enter_winkle:
>  
>  	IDLE_STATE_ENTER_SEQ_NORET(PPC_WINKLE)
>  
> +
> +/*
> + * power_enter_stop_lite : This will resume the wake up from
> + * idle at the subsequent instruction.
> + *
> + * Caller should set ESL=EC=0 in PSSCR before calling
> + * this function.
> + *
> + */
> +power_enter_stop_lite:
> +	IDLE_STATE_ENTER_SEQ(PPC_STOP)
> +7:	li	r3,0  /* Since we didn't lose state, return 0 */
> +	b 	pnv_wakeup_noloss
> +
>  /*
>   * r3 - requested stop state
>   */
> @@ -333,13 +349,19 @@ ALT_FTR_SECTION_END_NESTED_IFSET(CPU_FTR_ARCH_207S, 66);		\
>  
>  /*
>   * r3 - requested stop state
> + * r4 - Indicates if the lite variant with ESL=EC=0 should be executed.
>   */
>  _GLOBAL(power9_idle_stop)
> -	LOAD_REG_IMMEDIATE(r4, PSSCR_HV_TEMPLATE)
> -	or	r4,r4,r3
> +	cmpdi	r4, 1
> +	bne	4f
> +	LOAD_REG_IMMEDIATE(r4, PSSCR_HV_TEMPLATE_LITE)
> +	LOAD_REG_ADDR(r5,power_enter_stop_lite)
> +	b 	5f
> +4:	LOAD_REG_IMMEDIATE(r4, PSSCR_HV_TEMPLATE)
> +	LOAD_REG_ADDR(r5,power_enter_stop)
> +5:	or	r4,r4,r3
>  	mtspr	SPRN_PSSCR, r4
>  	li	r4, 1
> -	LOAD_REG_ADDR(r5,power_enter_stop)
>  	b	pnv_powersave_common
>  	/* No return */
>  /*
> diff --git a/arch/powerpc/platforms/powernv/idle.c b/arch/powerpc/platforms/powernv/idle.c
> index 479c256..c3d3fed 100644
> --- a/arch/powerpc/platforms/powernv/idle.c
> +++ b/arch/powerpc/platforms/powernv/idle.c
> @@ -244,8 +244,15 @@ static DEVICE_ATTR(fastsleep_workaround_applyonce, 0600,
>  static void power9_idle(void)
>  {
>  	/* Requesting stop state 0 */
> -	power9_idle_stop(0);
> +	power9_idle_stop(0, 0);
>  }
> +
> +static void power9_idle_lite(void)
> +{
> +	/* Requesting stop state 0 with ESL=EC=0 */
> +	power9_idle_stop(0, 1);
> +}
> +
>  /*
>   * First deep stop state. Used to figure out when to save/restore
>   * hypervisor context.
> @@ -414,8 +421,12 @@ static int __init pnv_init_idle_states(void)
>  
>  	if (supported_cpuidle_states & OPAL_PM_NAP_ENABLED)
>  		ppc_md.power_save = power7_idle;
> -	else if (supported_cpuidle_states & OPAL_PM_STOP_INST_FAST)
> -		ppc_md.power_save = power9_idle;
> +	else if (supported_cpuidle_states & OPAL_PM_STOP_INST_FAST) {
> +		if (supported_cpuidle_states & OPAL_PM_WAKEUP_AT_NEXT_INST)
> +			ppc_md.power_save = power9_idle_lite;
> +		else
> +			ppc_md.power_save = power9_idle;
> +	}

If I am reading this correctly we decide at boot time whether we support
wakeup at next instruction and make that the default sleep state. I am a little
surprised that these are exclusive. I was expecting power9_idle_lite to be
one of the states to go into before power9_idle

Balbir Singh.

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#1487145 — Re: [PATCH 2/2] powernv:idle:Implement lite variant of power_enter_stop

FromGautham R Shenoy <ego@linux.vnet.ibm.com>
Date2016-09-20 10:40 +0200
SubjectRe: [PATCH 2/2] powernv:idle:Implement lite variant of power_enter_stop
Message-ID<sjoKR-y5-3@gated-at.bofh.it>
In reply to#1487071
Hi Balbir,

On Tue, Sep 20, 2016 at 03:54:43PM +1000, Balbir Singh wrote:
> > diff --git a/arch/powerpc/platforms/powernv/idle.c b/arch/powerpc/platforms/powernv/idle.c
> > index 479c256..c3d3fed 100644
> > --- a/arch/powerpc/platforms/powernv/idle.c
> > +++ b/arch/powerpc/platforms/powernv/idle.c
> > @@ -244,8 +244,15 @@ static DEVICE_ATTR(fastsleep_workaround_applyonce, 0600,
> >  static void power9_idle(void)
> >  {
> >  	/* Requesting stop state 0 */
> > -	power9_idle_stop(0);
> > +	power9_idle_stop(0, 0);
> >  }
> > +
> > +static void power9_idle_lite(void)
> > +{
> > +	/* Requesting stop state 0 with ESL=EC=0 */
> > +	power9_idle_stop(0, 1);
> > +}
> > +
> >  /*
> >   * First deep stop state. Used to figure out when to save/restore
> >   * hypervisor context.
> > @@ -414,8 +421,12 @@ static int __init pnv_init_idle_states(void)
> >  
> >  	if (supported_cpuidle_states & OPAL_PM_NAP_ENABLED)
> >  		ppc_md.power_save = power7_idle;
> > -	else if (supported_cpuidle_states & OPAL_PM_STOP_INST_FAST)
> > -		ppc_md.power_save = power9_idle;
> > +	else if (supported_cpuidle_states & OPAL_PM_STOP_INST_FAST) {
> > +		if (supported_cpuidle_states & OPAL_PM_WAKEUP_AT_NEXT_INST)
> > +			ppc_md.power_save = power9_idle_lite;
> > +		else
> > +			ppc_md.power_save = power9_idle;
> > +	}
> 
> If I am reading this correctly we decide at boot time whether we support
> wakeup at next instruction and make that the default sleep state.
> I am a little surprised that these are exclusive. I was expecting
> power9_idle_lite to be one of the states to go into before
> power9_idle

At boot time, we initialize ppc_md.power_save to
power9_idle/power9_idle_lite which ends up being the default idle
function in the absence of the cpuidle subsystem. When cpuidle is
available, idle code will call cpuidle governors which will determine
the appropriate idle state that can be entered into. Each of these
idle states has an associated callback function. In case of the
idle-states without OPAL_PM_STOP_INST_FAST associated with them, the
callback is stop_loop() and when the flag is set, the callback
function is stop_lite_loop().  So when cpuidle is present, these
states are not exclusive.

Note that both power9_idle() and power9_idle_lite() call stop0. Just
that the former executes stop0 with ESL=EC=1 and latter with ESL=EC=0.

That said, you're right that in the absence of the cpuidle governor,
if the lite variant of stop is advertised by the firmware through the
device-tree, we end up picking the liter version of stop0 as the
default idle state. Do you suggest that we retain power9_idle which
calls stop0 with ESL=EC=1 ? 

> Balbir Singh.
> 
--
Thanks and Regards
gautham.

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#1489946

FromMichael Ellerman <mpe@ellerman.id.au>
Date2016-09-23 13:10 +0200
Message-ID<skwwF-2RT-9@gated-at.bofh.it>
In reply to#1484846
"Gautham R. Shenoy" <ego@linux.vnet.ibm.com> writes:

> From: "Gautham R. Shenoy" <ego@linux.vnet.ibm.com>
>
> This patch adds a function named power_enter_stop_lite() that can
> execute a stop instruction when ESL and EC bits are set to zero in the
> PSSCR.  The function handles the wake-up from idle at the instruction
> immediately after the stop instruction.
>
> If the flag OPAL_PM_WAKEUP_AT_NEXT_INST[1] is set in the device tree
> for a stop state, then use the lite variant for that particular stop
> state.

Hi Gautham,

It seems to me that this would be cleaner if it was modelled as a new
stop state? Surely it must have different power saving characteristics
to the existing state?

> [1] : The corresponding patch in skiboot that defines
>       OPAL_PM_WAKEUP_AT_NEXT_INST and enables it in the device tree
>       can be found here:
>       https://lists.ozlabs.org/pipermail/skiboot/2016-September/004805.html

Which says "This will reduce the exit latency of the idle state", and
yet it doesn't change any of the latency/residency values?

If all it does is reduce the exit latency, then shouldn't we always use
it? Presumably it also saves less power?

> diff --git a/arch/powerpc/kernel/idle_book3s.S b/arch/powerpc/kernel/idle_book3s.S
> index 32d666b..47ee106 100644
> --- a/arch/powerpc/kernel/idle_book3s.S
> +++ b/arch/powerpc/kernel/idle_book3s.S
> @@ -43,6 +43,8 @@
>  #define PSSCR_HV_TEMPLATE	PSSCR_ESL | PSSCR_EC | \
>  				PSSCR_PSLL_MASK | PSSCR_TR_MASK | \
>  				PSSCR_MTL_MASK
> +#define PSSCR_HV_TEMPLATE_LITE	PSSCR_PSLL_MASK | PSSCR_TR_MASK | \
> +				 PSSCR_MTL_MASK

Why do we have these at all? Firmware tells us the PSSCR values to use
in the "ibm,cpu-idle-state-psscr" property.

If we just used what firmware gave us then we wouldn't need the above,
or the juggling below.

> @@ -333,13 +349,19 @@ ALT_FTR_SECTION_END_NESTED_IFSET(CPU_FTR_ARCH_207S, 66);		\
>  
>  /*
>   * r3 - requested stop state
> + * r4 - Indicates if the lite variant with ESL=EC=0 should be executed.
>   */
>  _GLOBAL(power9_idle_stop)
> -	LOAD_REG_IMMEDIATE(r4, PSSCR_HV_TEMPLATE)
> -	or	r4,r4,r3
> +	cmpdi	r4, 1
> +	bne	4f
> +	LOAD_REG_IMMEDIATE(r4, PSSCR_HV_TEMPLATE_LITE)
> +	LOAD_REG_ADDR(r5,power_enter_stop_lite)
> +	b 	5f
> +4:	LOAD_REG_IMMEDIATE(r4, PSSCR_HV_TEMPLATE)
> +	LOAD_REG_ADDR(r5,power_enter_stop)
> +5:	or	r4,r4,r3
>  	mtspr	SPRN_PSSCR, r4
>  	li	r4, 1
> -	LOAD_REG_ADDR(r5,power_enter_stop)
>  	b	pnv_powersave_common
>  	/* No return */
>  /*

> diff --git a/arch/powerpc/platforms/powernv/idle.c b/arch/powerpc/platforms/powernv/idle.c
> index 479c256..c3d3fed 100644
> --- a/arch/powerpc/platforms/powernv/idle.c
> +++ b/arch/powerpc/platforms/powernv/idle.c
> @@ -244,8 +244,15 @@ static DEVICE_ATTR(fastsleep_workaround_applyonce, 0600,
>  static void power9_idle(void)
>  {
>  	/* Requesting stop state 0 */
> -	power9_idle_stop(0);
>  }

That seems like the root of the problem, why aren't we passing a PSSCR
value here?

I also don't see us using the psscr-mask property anywhere. Why isn't
that a bug?

cheers

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#1490123 — Re: [PATCH 2/2] powernv:idle:Implement lite variant of power_enter_stop

FromGautham R Shenoy <ego@linux.vnet.ibm.com>
Date2016-09-23 15:50 +0200
SubjectRe: [PATCH 2/2] powernv:idle:Implement lite variant of power_enter_stop
Message-ID<skz1x-4hK-69@gated-at.bofh.it>
In reply to#1489946
Hi Michael,

On Fri, Sep 23, 2016 at 09:03:45PM +1000, Michael Ellerman wrote:
> "Gautham R. Shenoy" <ego@linux.vnet.ibm.com> writes:
> 
> > From: "Gautham R. Shenoy" <ego@linux.vnet.ibm.com>
> >
> > This patch adds a function named power_enter_stop_lite() that can
> > execute a stop instruction when ESL and EC bits are set to zero in the
> > PSSCR.  The function handles the wake-up from idle at the instruction
> > immediately after the stop instruction.
> >
> > If the flag OPAL_PM_WAKEUP_AT_NEXT_INST[1] is set in the device tree
> > for a stop state, then use the lite variant for that particular stop
> > state.
> 
> Hi Gautham,
> 
> It seems to me that this would be cleaner if it was modelled as a new
> stop state? Surely it must have different power saving characteristics
> to the existing state?

It is supposed to be a new stop state, whose behaviour is different
from the existing stop states in terms of where it wakes up from stop.

You are right, it has different power saving characteristics to the
existing state.

> 
> > [1] : The corresponding patch in skiboot that defines
> >       OPAL_PM_WAKEUP_AT_NEXT_INST and enables it in the device tree
> >       can be found here:
> >       https://lists.ozlabs.org/pipermail/skiboot/2016-September/004805.html
> 
> Which says "This will reduce the exit latency of the idle state", and
> yet it doesn't change any of the latency/residency values?
> 
> If all it does is reduce the exit latency, then shouldn't we always use
> it? Presumably it also saves less power?

It does save less power compared to the corresponding variant where
ESL=EC=1.

> 
> > diff --git a/arch/powerpc/kernel/idle_book3s.S b/arch/powerpc/kernel/idle_book3s.S
> > index 32d666b..47ee106 100644
> > --- a/arch/powerpc/kernel/idle_book3s.S
> > +++ b/arch/powerpc/kernel/idle_book3s.S
> > @@ -43,6 +43,8 @@
> >  #define PSSCR_HV_TEMPLATE	PSSCR_ESL | PSSCR_EC | \
> >  				PSSCR_PSLL_MASK | PSSCR_TR_MASK | \
> >  				PSSCR_MTL_MASK
> > +#define PSSCR_HV_TEMPLATE_LITE	PSSCR_PSLL_MASK | PSSCR_TR_MASK | \
> > +				 PSSCR_MTL_MASK
> 
> Why do we have these at all? Firmware tells us the PSSCR values to use
> in the "ibm,cpu-idle-state-psscr" property.
> 
> If we just used what firmware gave us then we wouldn't need the above,
> or the juggling below.

Let me rework the patch to use the cpu-idle-state-psscr property which
is currently set to 0 in the firmware and
cpu-idle-state-psscr-mask which is set to 0xF for all the stop
states.

I agree, we can do without the hardcoding of the mask in the
kernel.

> 
> > @@ -333,13 +349,19 @@ ALT_FTR_SECTION_END_NESTED_IFSET(CPU_FTR_ARCH_207S, 66);		\
> >  
> >  /*
> >   * r3 - requested stop state
> > + * r4 - Indicates if the lite variant with ESL=EC=0 should be executed.
> >   */
> >  _GLOBAL(power9_idle_stop)
> > -	LOAD_REG_IMMEDIATE(r4, PSSCR_HV_TEMPLATE)
> > -	or	r4,r4,r3
> > +	cmpdi	r4, 1
> > +	bne	4f
> > +	LOAD_REG_IMMEDIATE(r4, PSSCR_HV_TEMPLATE_LITE)
> > +	LOAD_REG_ADDR(r5,power_enter_stop_lite)
> > +	b 	5f
> > +4:	LOAD_REG_IMMEDIATE(r4, PSSCR_HV_TEMPLATE)
> > +	LOAD_REG_ADDR(r5,power_enter_stop)
> > +5:	or	r4,r4,r3
> >  	mtspr	SPRN_PSSCR, r4
> >  	li	r4, 1
> > -	LOAD_REG_ADDR(r5,power_enter_stop)
> >  	b	pnv_powersave_common
> >  	/* No return */
> >  /*
> 
> > diff --git a/arch/powerpc/platforms/powernv/idle.c b/arch/powerpc/platforms/powernv/idle.c
> > index 479c256..c3d3fed 100644
> > --- a/arch/powerpc/platforms/powernv/idle.c
> > +++ b/arch/powerpc/platforms/powernv/idle.c
> > @@ -244,8 +244,15 @@ static DEVICE_ATTR(fastsleep_workaround_applyonce, 0600,
> >  static void power9_idle(void)
> >  {
> >  	/* Requesting stop state 0 */
> > -	power9_idle_stop(0);
> >  }
> 
> That seems like the root of the problem, why aren't we passing a PSSCR
> value here?
> 
> I also don't see us using the psscr-mask property anywhere. Why isn't
> that a bug?

Because we are only setting the Requested Level field which is the
bottom 4 bits. Everything else is taken from the hardcoded mask, which
is not incorrect, but not a very flexible design.

Thanks for the comments Michael. I will come back with a cleaner
patch.

> 
> cheers
> 

--
Thanks and Regards
gautham.

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