[PATCH 0/3] Fix RTC and NVRAM OPAL_BUSY loops

[PATCH 0/3] Fix RTC and NVRAM OPAL_BUSY loops

[Nicholas Piggin]

This is a couple of important fixes broken out of the series
"first step of standardising OPAL_BUSY handling", that prevents
the kernel from locking up if the NVRAM or RTC hardware does not
respond.

Another one, the console driver, has a similar problem that has
also been hit in testing, but that requires larger fixes to the
opal console and hvc tty driver that won't make it for 4.17.

Thanks,
Nick

Nicholas Piggin (3):
  powerpc/powernv: define a standard delay for OPAL_BUSY type retry
    loops
  powerpc/powernv: Fix OPAL RTC driver OPAL_BUSY loops
  powerpc/powernv: Fix OPAL NVRAM driver OPAL_BUSY loops

 arch/powerpc/include/asm/opal.h             |  3 ++
 arch/powerpc/platforms/powernv/opal-nvram.c |  7 +++-
 arch/powerpc/platforms/powernv/opal-rtc.c   |  8 +++--
 drivers/rtc/rtc-opal.c                      | 37 +++++++++++++--------
 4 files changed, 37 insertions(+), 18 deletions(-)

-- 
2.17.0

[PATCH 1/3] powerpc/powernv: define a standard delay for OPAL_BUSY type retry loops

[Nicholas Piggin]

This is the start of an effort to tidy up and standardise all the
delays. Existing loops have a range of delay/sleep periods from 1ms
to 20ms, and some have no delay. They all loop forever except rtc,
which times out after 10 retries, and that uses 10ms delays. So use
10ms as our standard delay. The OPAL maintainer agrees 10ms is a
reasonable starting point.

The idea is to use the same recipe everywhere, once this is proven to
work then it will be documented as an OPAL API standard. Then both
firmware and OS can agree, and if a particular call needs something
else, then that can be documented with reasoning.

This is not the end-all of this effort, it's just a relatively easy
change that fixes some existing high latency delays. There should be
provision for standardising timeouts and/or interruptible loops where
possible, so non-fatal firmware errors don't cause hangs.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
---
 arch/powerpc/include/asm/opal.h | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/powerpc/include/asm/opal.h b/arch/powerpc/include/asm/opal.h
index 7159e1a6a61a..03e1a920491e 100644
--- a/arch/powerpc/include/asm/opal.h
+++ b/arch/powerpc/include/asm/opal.h
@@ -21,6 +21,9 @@
 /* We calculate number of sg entries based on PAGE_SIZE */
 #define SG_ENTRIES_PER_NODE ((PAGE_SIZE - 16) / sizeof(struct opal_sg_entry))
 
+/* Default time to sleep or delay between OPAL_BUSY/OPAL_BUSY_EVENT loops */
+#define OPAL_BUSY_DELAY_MS	10
+
 /* /sys/firmware/opal */
 extern struct kobject *opal_kobj;
 
-- 
2.17.0

Re: [1/3] powerpc/powernv: define a standard delay for OPAL_BUSY type retry loops

[Michael Ellerman]

On Tue, 2018-04-10 at 11:49:31 UTC, Nicholas Piggin wrote:
> This is the start of an effort to tidy up and standardise all the
> delays. Existing loops have a range of delay/sleep periods from 1ms
> to 20ms, and some have no delay. They all loop forever except rtc,
> which times out after 10 retries, and that uses 10ms delays. So use
> 10ms as our standard delay. The OPAL maintainer agrees 10ms is a
> reasonable starting point.
> 
> The idea is to use the same recipe everywhere, once this is proven to
> work then it will be documented as an OPAL API standard. Then both
> firmware and OS can agree, and if a particular call needs something
> else, then that can be documented with reasoning.
> 
> This is not the end-all of this effort, it's just a relatively easy
> change that fixes some existing high latency delays. There should be
> provision for standardising timeouts and/or interruptible loops where
> possible, so non-fatal firmware errors don't cause hangs.
> 
> Signed-off-by: Nicholas Piggin <npiggin@gmail.com>

Applied to powerpc fixes, thanks.

https://git.kernel.org/powerpc/c/34dd25de9fe3f60bfdb31b473bf04b

cheers

[PATCH 2/3] powerpc/powernv: Fix OPAL RTC driver OPAL_BUSY loops

[Nicholas Piggin]

The OPAL RTC driver does not sleep in case it gets OPAL_BUSY or
OPAL_BUSY_EVENT from firmware, which causes large scheduling
latencies, up to 50 seconds have been observed here when RTC stops
responding (BMC reboot can do it).

Fix this by converting it to the standard form OPAL_BUSY loop that
sleeps.

Fixes 628daa8d5abfd ("powerpc/powernv: Add RTC and NVRAM support plus RTAS fallbacks"
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: linux-rtc@vger.kernel.org
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
---
 arch/powerpc/platforms/powernv/opal-rtc.c |  8 +++--
 drivers/rtc/rtc-opal.c                    | 37 ++++++++++++++---------
 2 files changed, 28 insertions(+), 17 deletions(-)

diff --git a/arch/powerpc/platforms/powernv/opal-rtc.c b/arch/powerpc/platforms/powernv/opal-rtc.c
index f8868864f373..aa2a5139462e 100644
--- a/arch/powerpc/platforms/powernv/opal-rtc.c
+++ b/arch/powerpc/platforms/powernv/opal-rtc.c
@@ -48,10 +48,12 @@ unsigned long __init opal_get_boot_time(void)
 
 	while (rc == OPAL_BUSY || rc == OPAL_BUSY_EVENT) {
 		rc = opal_rtc_read(&__y_m_d, &__h_m_s_ms);
-		if (rc == OPAL_BUSY_EVENT)
+		if (rc == OPAL_BUSY_EVENT) {
+			mdelay(OPAL_BUSY_DELAY_MS);
 			opal_poll_events(NULL);
-		else if (rc == OPAL_BUSY)
-			mdelay(10);
+		} else if (rc == OPAL_BUSY) {
+			mdelay(OPAL_BUSY_DELAY_MS);
+		}
 	}
 	if (rc != OPAL_SUCCESS)
 		return 0;
diff --git a/drivers/rtc/rtc-opal.c b/drivers/rtc/rtc-opal.c
index 304e891e35fc..60f2250fd96b 100644
--- a/drivers/rtc/rtc-opal.c
+++ b/drivers/rtc/rtc-opal.c
@@ -57,7 +57,7 @@ static void tm_to_opal(struct rtc_time *tm, u32 *y_m_d, u64 *h_m_s_ms)
 
 static int opal_get_rtc_time(struct device *dev, struct rtc_time *tm)
 {
-	long rc = OPAL_BUSY;
+	s64 rc = OPAL_BUSY;
 	int retries = 10;
 	u32 y_m_d;
 	u64 h_m_s_ms;
@@ -66,13 +66,17 @@ static int opal_get_rtc_time(struct device *dev, struct rtc_time *tm)
 
 	while (rc == OPAL_BUSY || rc == OPAL_BUSY_EVENT) {
 		rc = opal_rtc_read(&__y_m_d, &__h_m_s_ms);
-		if (rc == OPAL_BUSY_EVENT)
+		if (rc == OPAL_BUSY_EVENT) {
+			msleep(OPAL_BUSY_DELAY_MS);
 			opal_poll_events(NULL);
-		else if (retries-- && (rc == OPAL_HARDWARE
-				       || rc == OPAL_INTERNAL_ERROR))
-			msleep(10);
-		else if (rc != OPAL_BUSY && rc != OPAL_BUSY_EVENT)
-			break;
+		} else if (rc == OPAL_BUSY) {
+			msleep(OPAL_BUSY_DELAY_MS);
+		} else if (rc == OPAL_HARDWARE || rc == OPAL_INTERNAL_ERROR) {
+			if (retries--) {
+				msleep(10); /* Wait 10ms before retry */
+				rc = OPAL_BUSY; /* go around again */
+			}
+		}
 	}
 
 	if (rc != OPAL_SUCCESS)
@@ -87,21 +91,26 @@ static int opal_get_rtc_time(struct device *dev, struct rtc_time *tm)
 
 static int opal_set_rtc_time(struct device *dev, struct rtc_time *tm)
 {
-	long rc = OPAL_BUSY;
+	s64 rc = OPAL_BUSY;
 	int retries = 10;
 	u32 y_m_d = 0;
 	u64 h_m_s_ms = 0;
 
 	tm_to_opal(tm, &y_m_d, &h_m_s_ms);
+
 	while (rc == OPAL_BUSY || rc == OPAL_BUSY_EVENT) {
 		rc = opal_rtc_write(y_m_d, h_m_s_ms);
-		if (rc == OPAL_BUSY_EVENT)
+		if (rc == OPAL_BUSY_EVENT) {
+			msleep(OPAL_BUSY_DELAY_MS);
 			opal_poll_events(NULL);
-		else if (retries-- && (rc == OPAL_HARDWARE
-				       || rc == OPAL_INTERNAL_ERROR))
-			msleep(10);
-		else if (rc != OPAL_BUSY && rc != OPAL_BUSY_EVENT)
-			break;
+		} else if (rc == OPAL_BUSY) {
+			msleep(OPAL_BUSY_DELAY_MS);
+		} else if (rc == OPAL_HARDWARE || rc == OPAL_INTERNAL_ERROR) {
+			if (retries--) {
+				msleep(10); /* Wait 10ms before retry */
+				rc = OPAL_BUSY; /* go around again */
+			}
+		}
 	}
 
 	return rc == OPAL_SUCCESS ? 0 : -EIO;
-- 
2.17.0

Re: [PATCH 2/3] powerpc/powernv: Fix OPAL RTC driver OPAL_BUSY loops

[Alexandre Belloni]

Hi Nicholas,

I would greatly appreciate a changelog and at least the cover letter
because it is difficult to grasp how this relates to the previous
patches you sent to the RTC mailing list. 

On 10/04/2018 21:49:32+1000, Nicholas Piggin wrote:
> The OPAL RTC driver does not sleep in case it gets OPAL_BUSY or
> OPAL_BUSY_EVENT from firmware, which causes large scheduling
> latencies, up to 50 seconds have been observed here when RTC stops
> responding (BMC reboot can do it).
> 
> Fix this by converting it to the standard form OPAL_BUSY loop that
> sleeps.
> 
> Fixes 628daa8d5abfd ("powerpc/powernv: Add RTC and NVRAM support plus RTAS fallbacks"
> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> Cc: linux-rtc@vger.kernel.org
> Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
> ---
>  arch/powerpc/platforms/powernv/opal-rtc.c |  8 +++--
>  drivers/rtc/rtc-opal.c                    | 37 ++++++++++++++---------

>From what I understand, the changes in those files are fairly
independent, they should probably be separated to ease merging.

>  2 files changed, 28 insertions(+), 17 deletions(-)
> 
> diff --git a/arch/powerpc/platforms/powernv/opal-rtc.c b/arch/powerpc/platforms/powernv/opal-rtc.c
> index f8868864f373..aa2a5139462e 100644
> --- a/arch/powerpc/platforms/powernv/opal-rtc.c
> +++ b/arch/powerpc/platforms/powernv/opal-rtc.c
> @@ -48,10 +48,12 @@ unsigned long __init opal_get_boot_time(void)
>  
>  	while (rc == OPAL_BUSY || rc == OPAL_BUSY_EVENT) {
>  		rc = opal_rtc_read(&__y_m_d, &__h_m_s_ms);
> -		if (rc == OPAL_BUSY_EVENT)
> +		if (rc == OPAL_BUSY_EVENT) {
> +			mdelay(OPAL_BUSY_DELAY_MS);
>  			opal_poll_events(NULL);
> -		else if (rc == OPAL_BUSY)
> -			mdelay(10);
> +		} else if (rc == OPAL_BUSY) {
> +			mdelay(OPAL_BUSY_DELAY_MS);
> +		}
>  	}
>  	if (rc != OPAL_SUCCESS)
>  		return 0;
> diff --git a/drivers/rtc/rtc-opal.c b/drivers/rtc/rtc-opal.c
> index 304e891e35fc..60f2250fd96b 100644
> --- a/drivers/rtc/rtc-opal.c
> +++ b/drivers/rtc/rtc-opal.c
> @@ -57,7 +57,7 @@ static void tm_to_opal(struct rtc_time *tm, u32 *y_m_d, u64 *h_m_s_ms)
>  
>  static int opal_get_rtc_time(struct device *dev, struct rtc_time *tm)
>  {
> -	long rc = OPAL_BUSY;
> +	s64 rc = OPAL_BUSY;
>  	int retries = 10;
>  	u32 y_m_d;
>  	u64 h_m_s_ms;
> @@ -66,13 +66,17 @@ static int opal_get_rtc_time(struct device *dev, struct rtc_time *tm)
>  
>  	while (rc == OPAL_BUSY || rc == OPAL_BUSY_EVENT) {
>  		rc = opal_rtc_read(&__y_m_d, &__h_m_s_ms);
> -		if (rc == OPAL_BUSY_EVENT)
> +		if (rc == OPAL_BUSY_EVENT) {
> +			msleep(OPAL_BUSY_DELAY_MS);
>  			opal_poll_events(NULL);
> -		else if (retries-- && (rc == OPAL_HARDWARE
> -				       || rc == OPAL_INTERNAL_ERROR))
> -			msleep(10);
> -		else if (rc != OPAL_BUSY && rc != OPAL_BUSY_EVENT)
> -			break;
> +		} else if (rc == OPAL_BUSY) {
> +			msleep(OPAL_BUSY_DELAY_MS);
> +		} else if (rc == OPAL_HARDWARE || rc == OPAL_INTERNAL_ERROR) {
> +			if (retries--) {
> +				msleep(10); /* Wait 10ms before retry */
> +				rc = OPAL_BUSY; /* go around again */
> +			}
> +		}
>  	}
>  
>  	if (rc != OPAL_SUCCESS)
> @@ -87,21 +91,26 @@ static int opal_get_rtc_time(struct device *dev, struct rtc_time *tm)
>  
>  static int opal_set_rtc_time(struct device *dev, struct rtc_time *tm)
>  {
> -	long rc = OPAL_BUSY;
> +	s64 rc = OPAL_BUSY;
>  	int retries = 10;
>  	u32 y_m_d = 0;
>  	u64 h_m_s_ms = 0;
>  
>  	tm_to_opal(tm, &y_m_d, &h_m_s_ms);
> +
>  	while (rc == OPAL_BUSY || rc == OPAL_BUSY_EVENT) {
>  		rc = opal_rtc_write(y_m_d, h_m_s_ms);
> -		if (rc == OPAL_BUSY_EVENT)
> +		if (rc == OPAL_BUSY_EVENT) {
> +			msleep(OPAL_BUSY_DELAY_MS);
>  			opal_poll_events(NULL);
> -		else if (retries-- && (rc == OPAL_HARDWARE
> -				       || rc == OPAL_INTERNAL_ERROR))
> -			msleep(10);
> -		else if (rc != OPAL_BUSY && rc != OPAL_BUSY_EVENT)
> -			break;
> +		} else if (rc == OPAL_BUSY) {
> +			msleep(OPAL_BUSY_DELAY_MS);
> +		} else if (rc == OPAL_HARDWARE || rc == OPAL_INTERNAL_ERROR) {
> +			if (retries--) {
> +				msleep(10); /* Wait 10ms before retry */
> +				rc = OPAL_BUSY; /* go around again */
> +			}
> +		}
>  	}
>  
>  	return rc == OPAL_SUCCESS ? 0 : -EIO;
> -- 
> 2.17.0
> 

-- 
Alexandre Belloni, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
https://bootlin.com

Re: [PATCH 2/3] powerpc/powernv: Fix OPAL RTC driver OPAL_BUSY loops

[Nicholas Piggin]

On Tue, 10 Apr 2018 14:07:28 +0200
Alexandre Belloni <alexandre.belloni@bootlin.com> wrote:

> Hi Nicholas,
> 
> I would greatly appreciate a changelog and at least the cover letter
> because it is difficult to grasp how this relates to the previous
> patches you sent to the RTC mailing list. 

Yes good point. Basically this change is "standalone" except using
OPAL_BUSY_DELAY_MS define from patch 1. That patch has a lot of
comments about firmware delays I did not think would be too
interesting.

Basically we're adding msleep(10) here, because the firmware can
repeatedly return OPAL_BUSY for long periods, so we want to context
switch and respond to interrupts.

> 
> On 10/04/2018 21:49:32+1000, Nicholas Piggin wrote:
> > The OPAL RTC driver does not sleep in case it gets OPAL_BUSY or
> > OPAL_BUSY_EVENT from firmware, which causes large scheduling
> > latencies, up to 50 seconds have been observed here when RTC stops
> > responding (BMC reboot can do it).
> > 
> > Fix this by converting it to the standard form OPAL_BUSY loop that
> > sleeps.
> > 
> > Fixes 	 ("powerpc/powernv: Add RTC and NVRAM support plus RTAS fallbacks"
> > Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> > Cc: linux-rtc@vger.kernel.org
> > Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
> > ---
> >  arch/powerpc/platforms/powernv/opal-rtc.c |  8 +++--
> >  drivers/rtc/rtc-opal.c                    | 37 ++++++++++++++---------  
> 
> From what I understand, the changes in those files are fairly
> independent, they should probably be separated to ease merging.

I'm happy to do that. It's using the same firmware call, so I thought
a single patch would be fine. But I guess the boot call can be
dropped from this patch because it does not  not solve the problem
described in the changelog.

Would you be happy for the driver change to be merged via the powerpc
tree? The code being fixed here came from the same original patch as
a similar issue being fixed in the OPAL NVRAM driver so it might be
easier that way.

Thanks,
Nick

Re: [PATCH 2/3] powerpc/powernv: Fix OPAL RTC driver OPAL_BUSY loops

[Alexandre Belloni]

On 10/04/2018 23:01:36+1000, Nicholas Piggin wrote:
> On Tue, 10 Apr 2018 14:07:28 +0200
> Alexandre Belloni <alexandre.belloni@bootlin.com> wrote:
> > > Fixes 	 ("powerpc/powernv: Add RTC and NVRAM support plus RTAS fallbacks"
> > > Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> > > Cc: linux-rtc@vger.kernel.org
> > > Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
> > > ---
> > >  arch/powerpc/platforms/powernv/opal-rtc.c |  8 +++--
> > >  drivers/rtc/rtc-opal.c                    | 37 ++++++++++++++---------  
> > 
> > From what I understand, the changes in those files are fairly
> > independent, they should probably be separated to ease merging.
> 
> I'm happy to do that. It's using the same firmware call, so I thought
> a single patch would be fine. But I guess the boot call can be
> dropped from this patch because it does not  not solve the problem
> described in the changelog.
> 
> Would you be happy for the driver change to be merged via the powerpc
> tree? The code being fixed here came from the same original patch as
> a similar issue being fixed in the OPAL NVRAM driver so it might be
> easier that way.
> 

Ok then, just add my

Acked-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

and let it go through the powerpc tree.


-- 
Alexandre Belloni, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
https://bootlin.com

Re: [PATCH 2/3] powerpc/powernv: Fix OPAL RTC driver OPAL_BUSY loops

[Michael Ellerman]

Alexandre Belloni <alexandre.belloni@bootlin.com> writes:
> On 10/04/2018 23:01:36+1000, Nicholas Piggin wrote:
>> On Tue, 10 Apr 2018 14:07:28 +0200
>> Alexandre Belloni <alexandre.belloni@bootlin.com> wrote:
>> > > Fixes 	 ("powerpc/powernv: Add RTC and NVRAM support plus RTAS fallbacks"
>> > > Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
>> > > Cc: linux-rtc@vger.kernel.org
>> > > Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
>> > > ---
>> > >  arch/powerpc/platforms/powernv/opal-rtc.c |  8 +++--
>> > >  drivers/rtc/rtc-opal.c                    | 37 ++++++++++++++---------  
>> > 
>> > From what I understand, the changes in those files are fairly
>> > independent, they should probably be separated to ease merging.
>> 
>> I'm happy to do that. It's using the same firmware call, so I thought
>> a single patch would be fine. But I guess the boot call can be
>> dropped from this patch because it does not  not solve the problem
>> described in the changelog.
>> 
>> Would you be happy for the driver change to be merged via the powerpc
>> tree? The code being fixed here came from the same original patch as
>> a similar issue being fixed in the OPAL NVRAM driver so it might be
>> easier that way.
>
> Ok then, just add my
>
> Acked-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
>
> and let it go through the powerpc tree.

Thanks.

It's still mostly an rtc patch by lines changed, so I changed the
subject to:

  rtc: opal: Fix OPAL RTC driver OPAL_BUSY loops

cheers

Re: [PATCH 2/3] powerpc/powernv: Fix OPAL RTC driver OPAL_BUSY loops

[Alexandre Belloni]

On 25/04/2018 13:28:27+1000, Michael Ellerman wrote:
> Alexandre Belloni <alexandre.belloni@bootlin.com> writes:
> > On 10/04/2018 23:01:36+1000, Nicholas Piggin wrote:
> >> On Tue, 10 Apr 2018 14:07:28 +0200
> >> Alexandre Belloni <alexandre.belloni@bootlin.com> wrote:
> >> > > Fixes 	 ("powerpc/powernv: Add RTC and NVRAM support plus RTAS fallbacks"
> >> > > Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> >> > > Cc: linux-rtc@vger.kernel.org
> >> > > Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
> >> > > ---
> >> > >  arch/powerpc/platforms/powernv/opal-rtc.c |  8 +++--
> >> > >  drivers/rtc/rtc-opal.c                    | 37 ++++++++++++++---------  
> >> > 
> >> > From what I understand, the changes in those files are fairly
> >> > independent, they should probably be separated to ease merging.
> >> 
> >> I'm happy to do that. It's using the same firmware call, so I thought
> >> a single patch would be fine. But I guess the boot call can be
> >> dropped from this patch because it does not  not solve the problem
> >> described in the changelog.
> >> 
> >> Would you be happy for the driver change to be merged via the powerpc
> >> tree? The code being fixed here came from the same original patch as
> >> a similar issue being fixed in the OPAL NVRAM driver so it might be
> >> easier that way.
> >
> > Ok then, just add my
> >
> > Acked-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
> >
> > and let it go through the powerpc tree.
> 
> Thanks.
> 
> It's still mostly an rtc patch by lines changed, so I changed the
> subject to:
> 
>   rtc: opal: Fix OPAL RTC driver OPAL_BUSY loops
> 

Great, thanks!


-- 
Alexandre Belloni, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
https://bootlin.com

Re: [2/3] powerpc/powernv: Fix OPAL RTC driver OPAL_BUSY loops

[Michael Ellerman]

On Tue, 2018-04-10 at 11:49:32 UTC, Nicholas Piggin wrote:
> The OPAL RTC driver does not sleep in case it gets OPAL_BUSY or
> OPAL_BUSY_EVENT from firmware, which causes large scheduling
> latencies, up to 50 seconds have been observed here when RTC stops
> responding (BMC reboot can do it).
> 
> Fix this by converting it to the standard form OPAL_BUSY loop that
> sleeps.
> 
> Fixes 628daa8d5abfd ("powerpc/powernv: Add RTC and NVRAM support plus RTAS fallbacks"
> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> Cc: linux-rtc@vger.kernel.org
> Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
> Acked-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

Applied to powerpc fixes, thanks.

https://git.kernel.org/powerpc/c/682e6b4da5cbe8e9a53f979a58c2a9

cheers

[PATCH 3/3] powerpc/powernv: Fix OPAL NVRAM driver OPAL_BUSY loops

[Nicholas Piggin]

The OPAL NVRAM driver does not sleep in case it gets OPAL_BUSY or
OPAL_BUSY_EVENT from firmware, which causes large scheduling
latencies, and various lockup errors to trigger (again, BMC reboot
can cause it).

Fix this by converting it to the standard form OPAL_BUSY loop that
sleeps.

Fixes: 628daa8d5abfd ("powerpc/powernv: Add RTC and NVRAM support plus RTAS fallbacks")
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
---
 arch/powerpc/platforms/powernv/opal-nvram.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/platforms/powernv/opal-nvram.c b/arch/powerpc/platforms/powernv/opal-nvram.c
index ba2ff06a2c98..1bceb95f422d 100644
--- a/arch/powerpc/platforms/powernv/opal-nvram.c
+++ b/arch/powerpc/platforms/powernv/opal-nvram.c
@@ -11,6 +11,7 @@
 
 #define DEBUG
 
+#include <linux/delay.h>
 #include <linux/kernel.h>
 #include <linux/init.h>
 #include <linux/of.h>
@@ -56,8 +57,12 @@ static ssize_t opal_nvram_write(char *buf, size_t count, loff_t *index)
 
 	while (rc == OPAL_BUSY || rc == OPAL_BUSY_EVENT) {
 		rc = opal_write_nvram(__pa(buf), count, off);
-		if (rc == OPAL_BUSY_EVENT)
+		if (rc == OPAL_BUSY_EVENT) {
+			msleep(OPAL_BUSY_DELAY_MS);
 			opal_poll_events(NULL);
+		} else if (rc == OPAL_BUSY) {
+			msleep(OPAL_BUSY_DELAY_MS);
+		}
 	}
 
 	if (rc)
-- 
2.17.0

Re: [3/3] powerpc/powernv: Fix OPAL NVRAM driver OPAL_BUSY loops

[Michael Ellerman]

On Tue, 2018-04-10 at 11:49:33 UTC, Nicholas Piggin wrote:
> The OPAL NVRAM driver does not sleep in case it gets OPAL_BUSY or
> OPAL_BUSY_EVENT from firmware, which causes large scheduling
> latencies, and various lockup errors to trigger (again, BMC reboot
> can cause it).
> 
> Fix this by converting it to the standard form OPAL_BUSY loop that
> sleeps.
> 
> Fixes: 628daa8d5abfd ("powerpc/powernv: Add RTC and NVRAM support plus RTAS fallbacks")
> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> Signed-off-by: Nicholas Piggin <npiggin@gmail.com>

Applied to powerpc fixes, thanks.

https://git.kernel.org/powerpc/c/3b8070335f751aac9f1526ae2e012e

cheers