[PATCH] mtd: rawnand: Fix unexpected timeouts in waitrdy

[PATCH] mtd: rawnand: Fix unexpected timeouts in waitrdy

[Martin Devera]

The used way to compute jiffies timeout brokes when
jiffie difference is 1. Simply add 1 - it has no other
side effects.
Fixes STM32MP1 FMC2 NAND controller which sometimes failed
exactly in this way.

Signed-off-by: Martin Devera <devik@eaxlabs.cz>
---
 drivers/mtd/nand/raw/nand_base.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/mtd/nand/raw/nand_base.c b/drivers/mtd/nand/raw/nand_base.c
index d527e448ce19..beab3a775cc7 100644
--- a/drivers/mtd/nand/raw/nand_base.c
+++ b/drivers/mtd/nand/raw/nand_base.c
@@ -721,7 +721,11 @@ int nand_soft_waitrdy(struct nand_chip *chip, unsigned long timeout_ms)
 	if (ret)
 		return ret;
 
-	timeout_ms = jiffies + msecs_to_jiffies(timeout_ms);
+	/* +1 below is necessary because if we are now in the last fraction
+	 * of jiffy and msecs_to_jiffies is 1 then we will wait only that
+	 * small jiffy fraction - possibly leading to false timeout
+	 */
+	timeout_ms = jiffies + msecs_to_jiffies(timeout_ms) + 1;
 	do {
 		ret = nand_read_data_op(chip, &status, sizeof(status), true);
 		if (ret)
-- 
2.11.0


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Re: [PATCH] mtd: rawnand: Fix unexpected timeouts in waitrdy

[Miquel Raynal]

Hi Martin,

Martin Devera <devik@eaxlabs.cz> wrote on Tue, 10 Dec 2019 16:03:18
+0100:

> The used way to compute jiffies timeout brokes when
> jiffie difference is 1. Simply add 1 - it has no other
> side effects.
> Fixes STM32MP1 FMC2 NAND controller which sometimes failed
> exactly in this way.
> 
> Signed-off-by: Martin Devera <devik@eaxlabs.cz>
> ---
>  drivers/mtd/nand/raw/nand_base.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/mtd/nand/raw/nand_base.c b/drivers/mtd/nand/raw/nand_base.c
> index d527e448ce19..beab3a775cc7 100644
> --- a/drivers/mtd/nand/raw/nand_base.c
> +++ b/drivers/mtd/nand/raw/nand_base.c
> @@ -721,7 +721,11 @@ int nand_soft_waitrdy(struct nand_chip *chip, unsigned long timeout_ms)
>  	if (ret)
>  		return ret;
>  
> -	timeout_ms = jiffies + msecs_to_jiffies(timeout_ms);
> +	/* +1 below is necessary because if we are now in the last fraction
> +	 * of jiffy and msecs_to_jiffies is 1 then we will wait only that
> +	 * small jiffy fraction - possibly leading to false timeout
> +	 */
> +	timeout_ms = jiffies + msecs_to_jiffies(timeout_ms) + 1;
>  	do {
>  		ret = nand_read_data_op(chip, &status, sizeof(status), true);
>  		if (ret)

I don't really what you are fixing here, I suspect the root cause to be
a wrongly calculated timeout_ms in the calling driver.

It is the responsibility of the caller to use this function with a
relevant timeout_ms parameter. Maybe Christophe can help you here?


Thanks,
Miquèl

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Re: [PATCH] mtd: rawnand: Fix unexpected timeouts in waitrdy

[Martin DEVERA]

On 1/9/20 4:37 PM, Miquel Raynal wrote:
> Hi Martin,
>
> Martin Devera <devik@eaxlabs.cz> wrote on Tue, 10 Dec 2019 16:03:18
> +0100:
>
>> The used way to compute jiffies timeout brokes when
>> jiffie difference is 1. Simply add 1 - it has no other
>> side effects.
>> Fixes STM32MP1 FMC2 NAND controller which sometimes failed
>> exactly in this way.
>>
>> Signed-off-by: Martin Devera <devik@eaxlabs.cz>
>> ---
>>   drivers/mtd/nand/raw/nand_base.c | 6 +++++-
>>   1 file changed, 5 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/mtd/nand/raw/nand_base.c b/drivers/mtd/nand/raw/nand_base.c
>> index d527e448ce19..beab3a775cc7 100644
>> --- a/drivers/mtd/nand/raw/nand_base.c
>> +++ b/drivers/mtd/nand/raw/nand_base.c
>> @@ -721,7 +721,11 @@ int nand_soft_waitrdy(struct nand_chip *chip, unsigned long timeout_ms)
>>   	if (ret)
>>   		return ret;
>>   
>> -	timeout_ms = jiffies + msecs_to_jiffies(timeout_ms);
>> +	/* +1 below is necessary because if we are now in the last fraction
>> +	 * of jiffy and msecs_to_jiffies is 1 then we will wait only that
>> +	 * small jiffy fraction - possibly leading to false timeout
>> +	 */
>> +	timeout_ms = jiffies + msecs_to_jiffies(timeout_ms) + 1;
>>   	do {
>>   		ret = nand_read_data_op(chip, &status, sizeof(status), true);
>>   		if (ret)
> I don't really what you are fixing here, I suspect the root cause to be
> a wrongly calculated timeout_ms in the calling driver.
>
> It is the responsibility of the caller to use this function with a
> relevant timeout_ms parameter. Maybe Christophe can help you here?
>
Hi Miquel,

assume that nand_soft_waitrdy is called with timeout_ms==1. I suppose it is
valid case. Jiffies are 1000 for example (assume something more like 
1000.99 -
just before incrementing to 1001).
We compute timeout_ms = 1000+msecs_to_jiffies(1) = 1001 (at least for my 
jiffies rate).
nand_read_data_op is called for the first time and returns 0. During the 
call jiffies changes
to 1001 thus "while loop" ends here (wrongly).
Notice that routine was called with expected timeout 1ms but actual 
timeout used was something
between 0...1ms (which I also measured by tracing & scope on the bus).
Or is my analysis flawed somewhere ?

Thanks,

Martin


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Re: [PATCH] mtd: rawnand: Fix unexpected timeouts in waitrdy

[Miquel Raynal]

Hi Martin,

Martin DEVERA <devik@eaxlabs.cz> wrote on Thu, 9 Jan 2020 17:17:30
+0100:

> On 1/9/20 4:37 PM, Miquel Raynal wrote:
> > Hi Martin,
> >
> > Martin Devera <devik@eaxlabs.cz> wrote on Tue, 10 Dec 2019 16:03:18
> > +0100:
> >  
> >> The used way to compute jiffies timeout brokes when
> >> jiffie difference is 1. Simply add 1 - it has no other
> >> side effects.
> >> Fixes STM32MP1 FMC2 NAND controller which sometimes failed
> >> exactly in this way.
> >>
> >> Signed-off-by: Martin Devera <devik@eaxlabs.cz>
> >> ---
> >>   drivers/mtd/nand/raw/nand_base.c | 6 +++++-
> >>   1 file changed, 5 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/drivers/mtd/nand/raw/nand_base.c b/drivers/mtd/nand/raw/nand_base.c
> >> index d527e448ce19..beab3a775cc7 100644
> >> --- a/drivers/mtd/nand/raw/nand_base.c
> >> +++ b/drivers/mtd/nand/raw/nand_base.c
> >> @@ -721,7 +721,11 @@ int nand_soft_waitrdy(struct nand_chip *chip, unsigned long timeout_ms)
> >>   	if (ret)
> >>   		return ret;  
> >>   >> -	timeout_ms = jiffies + msecs_to_jiffies(timeout_ms);  
> >> +	/* +1 below is necessary because if we are now in the last fraction
> >> +	 * of jiffy and msecs_to_jiffies is 1 then we will wait only that
> >> +	 * small jiffy fraction - possibly leading to false timeout
> >> +	 */
> >> +	timeout_ms = jiffies + msecs_to_jiffies(timeout_ms) + 1;
> >>   	do {
> >>   		ret = nand_read_data_op(chip, &status, sizeof(status), true);
> >>   		if (ret)  
> > I don't really what you are fixing here, I suspect the root cause to be
> > a wrongly calculated timeout_ms in the calling driver.
> >
> > It is the responsibility of the caller to use this function with a
> > relevant timeout_ms parameter. Maybe Christophe can help you here?
> >  
> Hi Miquel,
> 
> assume that nand_soft_waitrdy is called with timeout_ms==1. I suppose it is
> valid case. Jiffies are 1000 for example (assume something more like 1000.99 -
> just before incrementing to 1001).
> We compute timeout_ms = 1000+msecs_to_jiffies(1) = 1001 (at least for my jiffies rate).
> nand_read_data_op is called for the first time and returns 0. During the call jiffies changes
> to 1001 thus "while loop" ends here (wrongly).
> Notice that routine was called with expected timeout 1ms but actual timeout used was something
> between 0...1ms (which I also measured by tracing & scope on the bus).
> Or is my analysis flawed somewhere ?

I agree with your analysis. Even if nand_soft_waitrdy will no longer be
used by the stm32 driver (Christophe sent a patch for that) I am fine
applying this change.

Could you add a comment to explain the '+1' and resend?

Thanks,
Miquèl

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Re: [PATCH] mtd: rawnand: Fix unexpected timeouts in waitrdy

[Miquel Raynal]

Hi Martin,

Martin DEVERA <devik@eaxlabs.cz> wrote on Thu, 9 Jan 2020 18:43:46
+0100:

> On 1/9/20 6:22 PM, Miquel Raynal wrote:
> > Hi Martin,
> >
> > Martin DEVERA <devik@eaxlabs.cz> wrote on Thu, 9 Jan 2020 17:17:30
> > +0100:
> >  
> >> On 1/9/20 4:37 PM, Miquel Raynal wrote:  
> >>> Hi Martin,
> >>>
> >>> Martin Devera <devik@eaxlabs.cz> wrote on Tue, 10 Dec 2019 16:03:18
> >>> +0100:  
> >>>   >>>> The used way to compute jiffies timeout brokes when  
> >>>> jiffie difference is 1. Simply add 1 - it has no other
> >>>> side effects.
> >>>> Fixes STM32MP1 FMC2 NAND controller which sometimes failed
> >>>> exactly in this way.
> >>>>
> >>>> Signed-off-by: Martin Devera <devik@eaxlabs.cz>
> >>>> ---
> >>>>    drivers/mtd/nand/raw/nand_base.c | 6 +++++-
> >>>>    1 file changed, 5 insertions(+), 1 deletion(-)
> >>>>
> >>>> diff --git a/drivers/mtd/nand/raw/nand_base.c b/drivers/mtd/nand/raw/nand_base.c
> >>>> index d527e448ce19..beab3a775cc7 100644
> >>>> --- a/drivers/mtd/nand/raw/nand_base.c
> >>>> +++ b/drivers/mtd/nand/raw/nand_base.c
> >>>> @@ -721,7 +721,11 @@ int nand_soft_waitrdy(struct nand_chip *chip, unsigned long timeout_ms)
> >>>>    	if (ret)
> >>>>    		return ret;  
> >>>>    >> -	timeout_ms = jiffies + msecs_to_jiffies(timeout_ms);  
> >>>> +	/* +1 below is necessary because if we are now in the last fraction
> >>>> +	 * of jiffy and msecs_to_jiffies is 1 then we will wait only that
> >>>> +	 * small jiffy fraction - possibly leading to false timeout
> >>>> +	 */
> >>>> +	timeout_ms = jiffies + msecs_to_jiffies(timeout_ms) + 1;
> >>>>    	do {
> >>>>    		ret = nand_read_data_op(chip, &status, sizeof(status), true);
> >>>>    		if (ret)  
> >>> I don't really what you are fixing here, I suspect the root cause to be
> >>> a wrongly calculated timeout_ms in the calling driver.
> >>>
> >>> It is the responsibility of the caller to use this function with a
> >>> relevant timeout_ms parameter. Maybe Christophe can help you here?  
> >>>   >> Hi Miquel,  
> >>
> >> assume that nand_soft_waitrdy is called with timeout_ms==1. I suppose it is
> >> valid case. Jiffies are 1000 for example (assume something more like 1000.99 -
> >> just before incrementing to 1001).
> >> We compute timeout_ms = 1000+msecs_to_jiffies(1) = 1001 (at least for my jiffies rate).
> >> nand_read_data_op is called for the first time and returns 0. During the call jiffies changes
> >> to 1001 thus "while loop" ends here (wrongly).
> >> Notice that routine was called with expected timeout 1ms but actual timeout used was something
> >> between 0...1ms (which I also measured by tracing & scope on the bus).
> >> Or is my analysis flawed somewhere ?  
> > I agree with your analysis. Even if nand_soft_waitrdy will no longer be
> > used by the stm32 driver (Christophe sent a patch for that) I am fine
> > applying this change.
> >
> > Could you add a comment to explain the '+1' and resend?
> >  
> Can you give me some guidance please ? Where should I add more comment to
> the git commit or to the C code ? I tried to comment both commit and code, probably
> you find the comments not clear enough ?

Sorry for not explaining: Could you add the example to the commit
message? The comment is fine, besides the fact that it should start
like this:

	/*
	 * Bla bla bla

Also please change the commit title, maybe

	mtd: rawnand: Ensure nand_soft_waitrdy wait period is enough

Thanks,
Miquèl

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Re: [PATCH] mtd: rawnand: Fix unexpected timeouts in waitrdy

[Miquel Raynal]

Hi Martin,

I forgot to mention: please don't forget to keep everyone in copy. I
re-added the mtd-list in my previous answer.

Miquel Raynal <miquel.raynal@bootlin.com> wrote on Thu, 9 Jan 2020
19:02:40 +0100:

> Hi Martin,
> 
> Martin DEVERA <devik@eaxlabs.cz> wrote on Thu, 9 Jan 2020 18:43:46
> +0100:
> 
> > On 1/9/20 6:22 PM, Miquel Raynal wrote:  
> > > Hi Martin,
> > >
> > > Martin DEVERA <devik@eaxlabs.cz> wrote on Thu, 9 Jan 2020 17:17:30
> > > +0100:
> > >    
> > >> On 1/9/20 4:37 PM, Miquel Raynal wrote:    
> > >>> Hi Martin,
> > >>>
> > >>> Martin Devera <devik@eaxlabs.cz> wrote on Tue, 10 Dec 2019 16:03:18
> > >>> +0100:    
> > >>>   >>>> The used way to compute jiffies timeout brokes when    
> > >>>> jiffie difference is 1. Simply add 1 - it has no other
> > >>>> side effects.
> > >>>> Fixes STM32MP1 FMC2 NAND controller which sometimes failed
> > >>>> exactly in this way.
> > >>>>
> > >>>> Signed-off-by: Martin Devera <devik@eaxlabs.cz>
> > >>>> ---
> > >>>>    drivers/mtd/nand/raw/nand_base.c | 6 +++++-
> > >>>>    1 file changed, 5 insertions(+), 1 deletion(-)
> > >>>>
> > >>>> diff --git a/drivers/mtd/nand/raw/nand_base.c b/drivers/mtd/nand/raw/nand_base.c
> > >>>> index d527e448ce19..beab3a775cc7 100644
> > >>>> --- a/drivers/mtd/nand/raw/nand_base.c
> > >>>> +++ b/drivers/mtd/nand/raw/nand_base.c
> > >>>> @@ -721,7 +721,11 @@ int nand_soft_waitrdy(struct nand_chip *chip, unsigned long timeout_ms)
> > >>>>    	if (ret)
> > >>>>    		return ret;    
> > >>>>    >> -	timeout_ms = jiffies + msecs_to_jiffies(timeout_ms);    
> > >>>> +	/* +1 below is necessary because if we are now in the last fraction
> > >>>> +	 * of jiffy and msecs_to_jiffies is 1 then we will wait only that
> > >>>> +	 * small jiffy fraction - possibly leading to false timeout
> > >>>> +	 */
> > >>>> +	timeout_ms = jiffies + msecs_to_jiffies(timeout_ms) + 1;
> > >>>>    	do {
> > >>>>    		ret = nand_read_data_op(chip, &status, sizeof(status), true);
> > >>>>    		if (ret)    
> > >>> I don't really what you are fixing here, I suspect the root cause to be
> > >>> a wrongly calculated timeout_ms in the calling driver.
> > >>>
> > >>> It is the responsibility of the caller to use this function with a
> > >>> relevant timeout_ms parameter. Maybe Christophe can help you here?    
> > >>>   >> Hi Miquel,    
> > >>
> > >> assume that nand_soft_waitrdy is called with timeout_ms==1. I suppose it is
> > >> valid case. Jiffies are 1000 for example (assume something more like 1000.99 -
> > >> just before incrementing to 1001).
> > >> We compute timeout_ms = 1000+msecs_to_jiffies(1) = 1001 (at least for my jiffies rate).
> > >> nand_read_data_op is called for the first time and returns 0. During the call jiffies changes
> > >> to 1001 thus "while loop" ends here (wrongly).
> > >> Notice that routine was called with expected timeout 1ms but actual timeout used was something
> > >> between 0...1ms (which I also measured by tracing & scope on the bus).
> > >> Or is my analysis flawed somewhere ?    
> > > I agree with your analysis. Even if nand_soft_waitrdy will no longer be
> > > used by the stm32 driver (Christophe sent a patch for that) I am fine
> > > applying this change.
> > >
> > > Could you add a comment to explain the '+1' and resend?
> > >    
> > Can you give me some guidance please ? Where should I add more comment to
> > the git commit or to the C code ? I tried to comment both commit and code, probably
> > you find the comments not clear enough ?  
> 
> Sorry for not explaining: Could you add the example to the commit
> message? The comment is fine, besides the fact that it should start
> like this:
> 
> 	/*
> 	 * Bla bla bla
> 
> Also please change the commit title, maybe
> 
> 	mtd: rawnand: Ensure nand_soft_waitrdy wait period is enough
> 
> Thanks,
> Miquèl




Thanks,
Miquèl

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[PATCH] mtd: rawnand: Ensure nand_soft_waitrdy wait period is enough

[Martin Devera]

The used way to compute jiffies timeout brokes when
jiffie difference is 1.
Assume that nand_soft_waitrdy is called with timeout_ms==1.
Jiffies are 1000 for example (assume something more like 1000.99
- just before incrementing to 1001).
We compute timeout_ms = 1000+msecs_to_jiffies(1) = 1001.
nand_read_data_op is called for the first time and returns 0.
During the call jiffies changes to 1001 thus "while loop" ends
here (wrongly). Notice that routine was called with expected timeout
1ms but actual timeout used was something between 0...1ms.

Fixes STM32MP1 FMC2 NAND controller which sometimes failed
exactly in this way.

Signed-off-by: Martin Devera <devik@eaxlabs.cz>
---
 drivers/mtd/nand/raw/nand_base.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/mtd/nand/raw/nand_base.c b/drivers/mtd/nand/raw/nand_base.c
index d527e448ce19..9a7e09c8d8be 100644
--- a/drivers/mtd/nand/raw/nand_base.c
+++ b/drivers/mtd/nand/raw/nand_base.c
@@ -721,7 +721,12 @@ int nand_soft_waitrdy(struct nand_chip *chip, unsigned long timeout_ms)
 	if (ret)
 		return ret;
 
-	timeout_ms = jiffies + msecs_to_jiffies(timeout_ms);
+	/*
+	 * +1 below is necessary because if we are now in the last fraction
+	 * of jiffy and msecs_to_jiffies is 1 then we will wait only that
+	 * small jiffy fraction - possibly leading to false timeout
+	 */
+	timeout_ms = jiffies + msecs_to_jiffies(timeout_ms) + 1;
 	do {
 		ret = nand_read_data_op(chip, &status, sizeof(status), true);
 		if (ret)
-- 
2.11.0


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Re: [PATCH] mtd: rawnand: Ensure nand_soft_waitrdy wait period is enough

[Miquel Raynal]

On Thu, 2020-01-16 at 13:54:31 UTC, Martin Devera wrote:
> The used way to compute jiffies timeout brokes when
> jiffie difference is 1.
> Assume that nand_soft_waitrdy is called with timeout_ms==1.
> Jiffies are 1000 for example (assume something more like 1000.99
> - just before incrementing to 1001).
> We compute timeout_ms = 1000+msecs_to_jiffies(1) = 1001.
> nand_read_data_op is called for the first time and returns 0.
> During the call jiffies changes to 1001 thus "while loop" ends
> here (wrongly). Notice that routine was called with expected timeout
> 1ms but actual timeout used was something between 0...1ms.
> 
> Fixes STM32MP1 FMC2 NAND controller which sometimes failed
> exactly in this way.
> 
> Signed-off-by: Martin Devera <devik@eaxlabs.cz>

Applied to https://git.kernel.org/pub/scm/linux/kernel/git/mtd/linux.git nand/next, thanks.

Miquel

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