[PATCH] staging: ade7754: Replace mlock with buf_lock and refactor code

[PATCH] staging: ade7754: Replace mlock with buf_lock and refactor code

[Gargi Sharma]

The IIO subsystem is redefining iio_dev->mlock to be used by
the IIO core only for protecting device operating mode changes.
ie. Changes between INDIO_DIRECT_MODE, INDIO_BUFFER_* modes.

In this driver, mlock was being used to protect hardware state
changes. Replace it with buf_lock in the devices global data.

As buf_lock already protects operations in ade7754_write_frequency,
there isn't a need to acquire the lock inside ade7754_spi_write_reg_8
when writing to the register.

Signed-off-by: Gargi Sharma <gs051095@gmail.com>
---
 drivers/staging/iio/meter/ade7754.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/drivers/staging/iio/meter/ade7754.c b/drivers/staging/iio/meter/ade7754.c
index 024463a..eb03469 100644
--- a/drivers/staging/iio/meter/ade7754.c
+++ b/drivers/staging/iio/meter/ade7754.c
@@ -29,6 +29,15 @@ static int ade7754_spi_write_reg_8(struct device *dev, u8 reg_address, u8 val)
 	struct iio_dev *indio_dev = dev_to_iio_dev(dev);
 	struct ade7754_state *st = iio_priv(indio_dev);
 
+	if (reg_address == ADE7754_WAVMODE) {
+		st->tx[0] = ADE7754_WRITE_REG(reg_address);
+		st->tx[1] = val;
+
+		ret = spi_write(st->us, st->tx, 2);
+
+		return ret;
+	}
+
 	mutex_lock(&st->buf_lock);
 	st->tx[0] = ADE7754_WRITE_REG(reg_address);
 	st->tx[1] = val;
@@ -430,7 +439,7 @@ static ssize_t ade7754_write_frequency(struct device *dev,
 	if (!val)
 		return -EINVAL;
 
-	mutex_lock(&indio_dev->mlock);
+	mutex_lock(&st->buf_lock);
 
 	t = 26000 / val;
 	if (t > 0)
@@ -451,7 +460,7 @@ static ssize_t ade7754_write_frequency(struct device *dev,
 	ret = ade7754_spi_write_reg_8(dev, ADE7754_WAVMODE, reg);
 
 out:
-	mutex_unlock(&indio_dev->mlock);
+	mutex_unlock(&st->buf_lock);
 
 	return ret ? ret : len;
 }
-- 
2.7.4

Re: [Outreachy kernel] [PATCH] staging: ade7754: Replace mlock with buf_lock and refactor code

[Alison Schofield]

On Mon, Mar 20, 2017 at 01:09:21PM +0530, Gargi Sharma wrote:
> The IIO subsystem is redefining iio_dev->mlock to be used by
> the IIO core only for protecting device operating mode changes.
> ie. Changes between INDIO_DIRECT_MODE, INDIO_BUFFER_* modes.
> 
> In this driver, mlock was being used to protect hardware state
> changes. Replace it with buf_lock in the devices global data.
> 
> As buf_lock already protects operations in ade7754_write_frequency,
> there isn't a need to acquire the lock inside ade7754_spi_write_reg_8
> when writing to the register.

Hi Gargi,

Looks like something went wrong in your patch below.  It doesn't do what
you say it'll do...Instead of removing the lock from _write_reg_8()
it inserts a bunch of code.  Anyway, it seems that w_rite_reg_8() is used
in multiple places, so removing that lock doesn't appear to be an
option.

See below...

alisons

> 
> Signed-off-by: Gargi Sharma <gs051095@gmail.com>
> ---
>  drivers/staging/iio/meter/ade7754.c | 13 +++++++++++--
>  1 file changed, 11 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/staging/iio/meter/ade7754.c b/drivers/staging/iio/meter/ade7754.c
> index 024463a..eb03469 100644
> --- a/drivers/staging/iio/meter/ade7754.c
> +++ b/drivers/staging/iio/meter/ade7754.c
> @@ -29,6 +29,15 @@ static int ade7754_spi_write_reg_8(struct device *dev, u8 reg_address, u8 val)
>  	struct iio_dev *indio_dev = dev_to_iio_dev(dev);
>  	struct ade7754_state *st = iio_priv(indio_dev);
>  
> +	if (reg_address == ADE7754_WAVMODE) {
> +		st->tx[0] = ADE7754_WRITE_REG(reg_address);
> +		st->tx[1] = val;
> +
> +		ret = spi_write(st->us, st->tx, 2);
> +
> +		return ret;
> +	}
> +
What's this?

>  	mutex_lock(&st->buf_lock);
>  	st->tx[0] = ADE7754_WRITE_REG(reg_address);
>  	st->tx[1] = val;
> @@ -430,7 +439,7 @@ static ssize_t ade7754_write_frequency(struct device *dev,
>  	if (!val)
>  		return -EINVAL;
>  
> -	mutex_lock(&indio_dev->mlock);
> +	mutex_lock(&st->buf_lock);
>  
>  	t = 26000 / val;
>  	if (t > 0)
> @@ -451,7 +460,7 @@ static ssize_t ade7754_write_frequency(struct device *dev,
>  	ret = ade7754_spi_write_reg_8(dev, ADE7754_WAVMODE, reg);
>  
>  out:
> -	mutex_unlock(&indio_dev->mlock);
> +	mutex_unlock(&st->buf_lock);
>  
>  	return ret ? ret : len;
>  }
> -- 
> 2.7.4
> 
> -- 
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> For more options, visit https://groups.google.com/d/optout.

Re: [Outreachy kernel] [PATCH] staging: ade7754: Replace mlock with buf_lock and refactor code

[Gargi Sharma]

On Tue, Mar 21, 2017 at 10:54 PM, Alison Schofield <amsfield22@gmail.com> wrote:
> On Mon, Mar 20, 2017 at 01:09:21PM +0530, Gargi Sharma wrote:
>> The IIO subsystem is redefining iio_dev->mlock to be used by
>> the IIO core only for protecting device operating mode changes.
>> ie. Changes between INDIO_DIRECT_MODE, INDIO_BUFFER_* modes.
>>
>> In this driver, mlock was being used to protect hardware state
>> changes. Replace it with buf_lock in the devices global data.
>>
>> As buf_lock already protects operations in ade7754_write_frequency,
>> there isn't a need to acquire the lock inside ade7754_spi_write_reg_8
>> when writing to the register.
>
> Hi Gargi,
>
> Looks like something went wrong in your patch below.  It doesn't do what
> you say it'll do...Instead of removing the lock from _write_reg_8()
> it inserts a bunch of code.  Anyway, it seems that w_rite_reg_8() is used
> in multiple places, so removing that lock doesn't appear to be an
> option.
>
> See below...
>
> alisons
>
>>
>> Signed-off-by: Gargi Sharma <gs051095@gmail.com>
>> ---
>>  drivers/staging/iio/meter/ade7754.c | 13 +++++++++++--
>>  1 file changed, 11 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/staging/iio/meter/ade7754.c b/drivers/staging/iio/meter/ade7754.c
>> index 024463a..eb03469 100644
>> --- a/drivers/staging/iio/meter/ade7754.c
>> +++ b/drivers/staging/iio/meter/ade7754.c
>> @@ -29,6 +29,15 @@ static int ade7754_spi_write_reg_8(struct device *dev, u8 reg_address, u8 val)
>>       struct iio_dev *indio_dev = dev_to_iio_dev(dev);
>>       struct ade7754_state *st = iio_priv(indio_dev);
>>
>> +     if (reg_address == ADE7754_WAVMODE) {
>> +             st->tx[0] = ADE7754_WRITE_REG(reg_address);
>> +             st->tx[1] = val;
>> +
>> +             ret = spi_write(st->us, st->tx, 2);
>> +
>> +             return ret;
>> +     }
>> +
> What's this?

When the function ade_spi_write_reg_8() is called inside
ade7754_write_frequency(), we are writing to this( ADE7754_WAVMODE)
register. When writing to this register we don't need to hold the
buf_lock since ade7754_write_frequency() already takes care of that.

>
>>       mutex_lock(&st->buf_lock);
>>       st->tx[0] = ADE7754_WRITE_REG(reg_address);
>>       st->tx[1] = val;
>> @@ -430,7 +439,7 @@ static ssize_t ade7754_write_frequency(struct device *dev,
>>       if (!val)
>>               return -EINVAL;
>>
>> -     mutex_lock(&indio_dev->mlock);
>> +     mutex_lock(&st->buf_lock);
>>
>>       t = 26000 / val;
>>       if (t > 0)
>> @@ -451,7 +460,7 @@ static ssize_t ade7754_write_frequency(struct device *dev,
>>       ret = ade7754_spi_write_reg_8(dev, ADE7754_WAVMODE, reg);
>>
>>  out:
>> -     mutex_unlock(&indio_dev->mlock);
>> +     mutex_unlock(&st->buf_lock);
>>
>>       return ret ? ret : len;
>>  }

The buf_lock inside ade7754_write_frequency() takes into account that
when using the function ade7754_spi_write_reg_8, lock is already held
and locking is no longer required inside the ade7754_spi_write_reg_8()
function.

Let me know if this sounds okay, I can perhaps edit the commit log to
make this clearer.

Thanks,
Gargi

>> --
>> 2.7.4
>>
>> --
>> You received this message because you are subscribed to the Google Groups "outreachy-kernel" group.
>> To unsubscribe from this group and stop receiving emails from it, send an email to outreachy-kernel+unsubscribe@googlegroups.com.
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>> To view this discussion on the web visit https://groups.google.com/d/msgid/outreachy-kernel/1489995561-6988-1-git-send-email-gs051095%40gmail.com.
>> For more options, visit https://groups.google.com/d/optout.
>
> --
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Re: [Outreachy kernel] [PATCH] staging: ade7754: Replace mlock with buf_lock and refactor code

[Alison Schofield]

On Tue, Mar 21, 2017 at 11:18:23PM +0530, Gargi Sharma wrote:
> On Tue, Mar 21, 2017 at 10:54 PM, Alison Schofield <amsfield22@gmail.com> wrote:
> > On Mon, Mar 20, 2017 at 01:09:21PM +0530, Gargi Sharma wrote:
> >> The IIO subsystem is redefining iio_dev->mlock to be used by
> >> the IIO core only for protecting device operating mode changes.
> >> ie. Changes between INDIO_DIRECT_MODE, INDIO_BUFFER_* modes.
> >>
> >> In this driver, mlock was being used to protect hardware state
> >> changes. Replace it with buf_lock in the devices global data.
> >>
> >> As buf_lock already protects operations in ade7754_write_frequency,
> >> there isn't a need to acquire the lock inside ade7754_spi_write_reg_8
> >> when writing to the register.
> >
> > Hi Gargi,
> >
> > Looks like something went wrong in your patch below.  It doesn't do what
> > you say it'll do...Instead of removing the lock from _write_reg_8()
> > it inserts a bunch of code.  Anyway, it seems that w_rite_reg_8() is used
> > in multiple places, so removing that lock doesn't appear to be an
> > option.
> >
> > See below...
> >
> > alisons
> >
> >>
> >> Signed-off-by: Gargi Sharma <gs051095@gmail.com>
> >> ---
> >>  drivers/staging/iio/meter/ade7754.c | 13 +++++++++++--
> >>  1 file changed, 11 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/drivers/staging/iio/meter/ade7754.c b/drivers/staging/iio/meter/ade7754.c
> >> index 024463a..eb03469 100644
> >> --- a/drivers/staging/iio/meter/ade7754.c
> >> +++ b/drivers/staging/iio/meter/ade7754.c
> >> @@ -29,6 +29,15 @@ static int ade7754_spi_write_reg_8(struct device *dev, u8 reg_address, u8 val)
> >>       struct iio_dev *indio_dev = dev_to_iio_dev(dev);
> >>       struct ade7754_state *st = iio_priv(indio_dev);
> >>
> >> +     if (reg_address == ADE7754_WAVMODE) {
> >> +             st->tx[0] = ADE7754_WRITE_REG(reg_address);
> >> +             st->tx[1] = val;
> >> +
> >> +             ret = spi_write(st->us, st->tx, 2);
> >> +
> >> +             return ret;
> >> +     }
> >> +
> > What's this?
> 
> When the function ade_spi_write_reg_8() is called inside
> ade7754_write_frequency(), we are writing to this( ADE7754_WAVMODE)
> register. When writing to this register we don't need to hold the
> buf_lock since ade7754_write_frequency() already takes care of that.

Oh! I see it now. You created a special 'no lock needed' case
inside of --write_reg_8 for  writing frequency.   That works, 
but it's...ummm...sneaky ;)  Let's see if there's another way.  

Look back at Lars suggestion on a similar patch.  Maybe that
will apply here.
http://marc.info/?l=linux-kernel&m=148940648615743&w=2

alisons


> 
> >
> >>       mutex_lock(&st->buf_lock);
> >>       st->tx[0] = ADE7754_WRITE_REG(reg_address);
> >>       st->tx[1] = val;
> >> @@ -430,7 +439,7 @@ static ssize_t ade7754_write_frequency(struct device *dev,
> >>       if (!val)
> >>               return -EINVAL;
> >>
> >> -     mutex_lock(&indio_dev->mlock);
> >> +     mutex_lock(&st->buf_lock);
> >>
> >>       t = 26000 / val;
> >>       if (t > 0)
> >> @@ -451,7 +460,7 @@ static ssize_t ade7754_write_frequency(struct device *dev,
> >>       ret = ade7754_spi_write_reg_8(dev, ADE7754_WAVMODE, reg);
> >>
> >>  out:
> >> -     mutex_unlock(&indio_dev->mlock);
> >> +     mutex_unlock(&st->buf_lock);
> >>
> >>       return ret ? ret : len;
> >>  }
> 
> The buf_lock inside ade7754_write_frequency() takes into account that
> when using the function ade7754_spi_write_reg_8, lock is already held
> and locking is no longer required inside the ade7754_spi_write_reg_8()
> function.
> 
> Let me know if this sounds okay, I can perhaps edit the commit log to
> make this clearer.
> 
> Thanks,
> Gargi
> 
> >> --
> >> 2.7.4
> >>
> >> --
> >> You received this message because you are subscribed to the Google Groups "outreachy-kernel" group.
> >> To unsubscribe from this group and stop receiving emails from it, send an email to outreachy-kernel+unsubscribe@googlegroups.com.
> >> To post to this group, send email to outreachy-kernel@googlegroups.com.
> >> To view this discussion on the web visit https://groups.google.com/d/msgid/outreachy-kernel/1489995561-6988-1-git-send-email-gs051095%40gmail.com.
> >> For more options, visit https://groups.google.com/d/optout.
> >
> > --
> > You received this message because you are subscribed to the Google Groups "outreachy-kernel" group.
> > To unsubscribe from this group and stop receiving emails from it, send an email to outreachy-kernel+unsubscribe@googlegroups.com.
> > To post to this group, send email to outreachy-kernel@googlegroups.com.
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> > For more options, visit https://groups.google.com/d/optout.

Re: [Outreachy kernel] [PATCH] staging: ade7754: Replace mlock with buf_lock and refactor code

[Gargi Sharma]

On Tue, Mar 21, 2017 at 11:42 PM, Alison Schofield <amsfield22@gmail.com> wrote:
> On Tue, Mar 21, 2017 at 11:18:23PM +0530, Gargi Sharma wrote:
>> On Tue, Mar 21, 2017 at 10:54 PM, Alison Schofield <amsfield22@gmail.com> wrote:
>> > On Mon, Mar 20, 2017 at 01:09:21PM +0530, Gargi Sharma wrote:
>> >> The IIO subsystem is redefining iio_dev->mlock to be used by
>> >> the IIO core only for protecting device operating mode changes.
>> >> ie. Changes between INDIO_DIRECT_MODE, INDIO_BUFFER_* modes.
>> >>
>> >> In this driver, mlock was being used to protect hardware state
>> >> changes. Replace it with buf_lock in the devices global data.
>> >>
>> >> As buf_lock already protects operations in ade7754_write_frequency,
>> >> there isn't a need to acquire the lock inside ade7754_spi_write_reg_8
>> >> when writing to the register.
>> >
>> > Hi Gargi,
>> >
>> > Looks like something went wrong in your patch below.  It doesn't do what
>> > you say it'll do...Instead of removing the lock from _write_reg_8()
>> > it inserts a bunch of code.  Anyway, it seems that w_rite_reg_8() is used
>> > in multiple places, so removing that lock doesn't appear to be an
>> > option.
>> >
>> > See below...
>> >
>> > alisons
>> >
>> >>
>> >> Signed-off-by: Gargi Sharma <gs051095@gmail.com>
>> >> ---
>> >>  drivers/staging/iio/meter/ade7754.c | 13 +++++++++++--
>> >>  1 file changed, 11 insertions(+), 2 deletions(-)
>> >>
>> >> diff --git a/drivers/staging/iio/meter/ade7754.c b/drivers/staging/iio/meter/ade7754.c
>> >> index 024463a..eb03469 100644
>> >> --- a/drivers/staging/iio/meter/ade7754.c
>> >> +++ b/drivers/staging/iio/meter/ade7754.c
>> >> @@ -29,6 +29,15 @@ static int ade7754_spi_write_reg_8(struct device *dev, u8 reg_address, u8 val)
>> >>       struct iio_dev *indio_dev = dev_to_iio_dev(dev);
>> >>       struct ade7754_state *st = iio_priv(indio_dev);
>> >>
>> >> +     if (reg_address == ADE7754_WAVMODE) {
>> >> +             st->tx[0] = ADE7754_WRITE_REG(reg_address);
>> >> +             st->tx[1] = val;
>> >> +
>> >> +             ret = spi_write(st->us, st->tx, 2);
>> >> +
>> >> +             return ret;
>> >> +     }
>> >> +
>> > What's this?
>>
>> When the function ade_spi_write_reg_8() is called inside
>> ade7754_write_frequency(), we are writing to this( ADE7754_WAVMODE)
>> register. When writing to this register we don't need to hold the
>> buf_lock since ade7754_write_frequency() already takes care of that.
>
> Oh! I see it now. You created a special 'no lock needed' case
> inside of --write_reg_8 for  writing frequency.   That works,
> but it's...ummm...sneaky ;)  Let's see if there's another way.
>
> Look back at Lars suggestion on a similar patch.  Maybe that
> will apply here.
> http://marc.info/?l=linux-kernel&m=148940648615743&w=2
>

I did look at the patch you suggested for inspiration :) What I could
not understand was the part where Lars wrote about "doing a
read-modify-write cycle in a protected section." I can write a
separate function for --write_reg_8 that does not take the lock, but
do not know how to do a "read-modify-write cycle in a protected
section" :(

Gargi
> alisons
>
>
>>
>> >
>> >>       mutex_lock(&st->buf_lock);
>> >>       st->tx[0] = ADE7754_WRITE_REG(reg_address);
>> >>       st->tx[1] = val;
>> >> @@ -430,7 +439,7 @@ static ssize_t ade7754_write_frequency(struct device *dev,
>> >>       if (!val)
>> >>               return -EINVAL;
>> >>
>> >> -     mutex_lock(&indio_dev->mlock);
>> >> +     mutex_lock(&st->buf_lock);
>> >>
>> >>       t = 26000 / val;
>> >>       if (t > 0)
>> >> @@ -451,7 +460,7 @@ static ssize_t ade7754_write_frequency(struct device *dev,
>> >>       ret = ade7754_spi_write_reg_8(dev, ADE7754_WAVMODE, reg);
>> >>
>> >>  out:
>> >> -     mutex_unlock(&indio_dev->mlock);
>> >> +     mutex_unlock(&st->buf_lock);
>> >>
>> >>       return ret ? ret : len;
>> >>  }
>>
>> The buf_lock inside ade7754_write_frequency() takes into account that
>> when using the function ade7754_spi_write_reg_8, lock is already held
>> and locking is no longer required inside the ade7754_spi_write_reg_8()
>> function.
>>
>> Let me know if this sounds okay, I can perhaps edit the commit log to
>> make this clearer.
>>
>> Thanks,
>> Gargi
>>
>> >> --
>> >> 2.7.4
>> >>
>> >> --
>> >> You received this message because you are subscribed to the Google Groups "outreachy-kernel" group.
>> >> To unsubscribe from this group and stop receiving emails from it, send an email to outreachy-kernel+unsubscribe@googlegroups.com.
>> >> To post to this group, send email to outreachy-kernel@googlegroups.com.
>> >> To view this discussion on the web visit https://groups.google.com/d/msgid/outreachy-kernel/1489995561-6988-1-git-send-email-gs051095%40gmail.com.
>> >> For more options, visit https://groups.google.com/d/optout.
>> >
>> > --
>> > You received this message because you are subscribed to the Google Groups "outreachy-kernel" group.
>> > To unsubscribe from this group and stop receiving emails from it, send an email to outreachy-kernel+unsubscribe@googlegroups.com.
>> > To post to this group, send email to outreachy-kernel@googlegroups.com.
>> > To view this discussion on the web visit https://groups.google.com/d/msgid/outreachy-kernel/20170321172438.GC2793%40d830.WORKGROUP.
>> > For more options, visit https://groups.google.com/d/optout.
>
> --
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Re: [Outreachy kernel] [PATCH] staging: ade7754: Replace mlock with buf_lock and refactor code

[Alison Schofield]

On Tue, Mar 21, 2017 at 11:48:27PM +0530, Gargi Sharma wrote:
> On Tue, Mar 21, 2017 at 11:42 PM, Alison Schofield <amsfield22@gmail.com> wrote:
> > On Tue, Mar 21, 2017 at 11:18:23PM +0530, Gargi Sharma wrote:
> >> On Tue, Mar 21, 2017 at 10:54 PM, Alison Schofield <amsfield22@gmail.com> wrote:
> >> > On Mon, Mar 20, 2017 at 01:09:21PM +0530, Gargi Sharma wrote:
> >> >> The IIO subsystem is redefining iio_dev->mlock to be used by
> >> >> the IIO core only for protecting device operating mode changes.
> >> >> ie. Changes between INDIO_DIRECT_MODE, INDIO_BUFFER_* modes.
> >> >>
> >> >> In this driver, mlock was being used to protect hardware state
> >> >> changes. Replace it with buf_lock in the devices global data.
> >> >>
> >> >> As buf_lock already protects operations in ade7754_write_frequency,
> >> >> there isn't a need to acquire the lock inside ade7754_spi_write_reg_8
> >> >> when writing to the register.
> >> >
> >> > Hi Gargi,
> >> >
> >> > Looks like something went wrong in your patch below.  It doesn't do what
> >> > you say it'll do...Instead of removing the lock from _write_reg_8()
> >> > it inserts a bunch of code.  Anyway, it seems that w_rite_reg_8() is used
> >> > in multiple places, so removing that lock doesn't appear to be an
> >> > option.
> >> >
> >> > See below...
> >> >
> >> > alisons
> >> >
> >> >>
> >> >> Signed-off-by: Gargi Sharma <gs051095@gmail.com>
> >> >> ---
> >> >>  drivers/staging/iio/meter/ade7754.c | 13 +++++++++++--
> >> >>  1 file changed, 11 insertions(+), 2 deletions(-)
> >> >>
> >> >> diff --git a/drivers/staging/iio/meter/ade7754.c b/drivers/staging/iio/meter/ade7754.c
> >> >> index 024463a..eb03469 100644
> >> >> --- a/drivers/staging/iio/meter/ade7754.c
> >> >> +++ b/drivers/staging/iio/meter/ade7754.c
> >> >> @@ -29,6 +29,15 @@ static int ade7754_spi_write_reg_8(struct device *dev, u8 reg_address, u8 val)
> >> >>       struct iio_dev *indio_dev = dev_to_iio_dev(dev);
> >> >>       struct ade7754_state *st = iio_priv(indio_dev);
> >> >>
> >> >> +     if (reg_address == ADE7754_WAVMODE) {
> >> >> +             st->tx[0] = ADE7754_WRITE_REG(reg_address);
> >> >> +             st->tx[1] = val;
> >> >> +
> >> >> +             ret = spi_write(st->us, st->tx, 2);
> >> >> +
> >> >> +             return ret;
> >> >> +     }
> >> >> +
> >> > What's this?
> >>
> >> When the function ade_spi_write_reg_8() is called inside
> >> ade7754_write_frequency(), we are writing to this( ADE7754_WAVMODE)
> >> register. When writing to this register we don't need to hold the
> >> buf_lock since ade7754_write_frequency() already takes care of that.
> >
> > Oh! I see it now. You created a special 'no lock needed' case
> > inside of --write_reg_8 for  writing frequency.   That works,
> > but it's...ummm...sneaky ;)  Let's see if there's another way.
> >
> > Look back at Lars suggestion on a similar patch.  Maybe that
> > will apply here.
> > http://marc.info/?l=linux-kernel&m=148940648615743&w=2
> >
> 
> I did look at the patch you suggested for inspiration :) What I could
> not understand was the part where Lars wrote about "doing a
> read-modify-write cycle in a protected section." I can write a
> separate function for --write_reg_8 that does not take the lock, but
> do not know how to do a "read-modify-write cycle in a protected
> section" :(
> 
> Gargi

Gargi - That's a great, specific question! Let's pop that back to Lars.

Lars - Can you explain further or perhaps point to a driver that does
something similar?

alisons

> > alisons
> >
> >
> >>
> >> >
> >> >>       mutex_lock(&st->buf_lock);
> >> >>       st->tx[0] = ADE7754_WRITE_REG(reg_address);
> >> >>       st->tx[1] = val;
> >> >> @@ -430,7 +439,7 @@ static ssize_t ade7754_write_frequency(struct device *dev,
> >> >>       if (!val)
> >> >>               return -EINVAL;
> >> >>
> >> >> -     mutex_lock(&indio_dev->mlock);
> >> >> +     mutex_lock(&st->buf_lock);
> >> >>
> >> >>       t = 26000 / val;
> >> >>       if (t > 0)
> >> >> @@ -451,7 +460,7 @@ static ssize_t ade7754_write_frequency(struct device *dev,
> >> >>       ret = ade7754_spi_write_reg_8(dev, ADE7754_WAVMODE, reg);
> >> >>
> >> >>  out:
> >> >> -     mutex_unlock(&indio_dev->mlock);
> >> >> +     mutex_unlock(&st->buf_lock);
> >> >>
> >> >>       return ret ? ret : len;
> >> >>  }
> >>
> >> The buf_lock inside ade7754_write_frequency() takes into account that
> >> when using the function ade7754_spi_write_reg_8, lock is already held
> >> and locking is no longer required inside the ade7754_spi_write_reg_8()
> >> function.
> >>
> >> Let me know if this sounds okay, I can perhaps edit the commit log to
> >> make this clearer.
> >>
> >> Thanks,
> >> Gargi
> >>
> >> >> --
> >> >> 2.7.4
> >> >>
> >> >> --
> >> >> You received this message because you are subscribed to the Google Groups "outreachy-kernel" group.
> >> >> To unsubscribe from this group and stop receiving emails from it, send an email to outreachy-kernel+unsubscribe@googlegroups.com.
> >> >> To post to this group, send email to outreachy-kernel@googlegroups.com.
> >> >> To view this discussion on the web visit https://groups.google.com/d/msgid/outreachy-kernel/1489995561-6988-1-git-send-email-gs051095%40gmail.com.
> >> >> For more options, visit https://groups.google.com/d/optout.
> >> >
> >> > --
> >> > You received this message because you are subscribed to the Google Groups "outreachy-kernel" group.
> >> > To unsubscribe from this group and stop receiving emails from it, send an email to outreachy-kernel+unsubscribe@googlegroups.com.
> >> > To post to this group, send email to outreachy-kernel@googlegroups.com.
> >> > To view this discussion on the web visit https://groups.google.com/d/msgid/outreachy-kernel/20170321172438.GC2793%40d830.WORKGROUP.
> >> > For more options, visit https://groups.google.com/d/optout.
> >
> > --
> > You received this message because you are subscribed to the Google Groups "outreachy-kernel" group.
> > To unsubscribe from this group and stop receiving emails from it, send an email to outreachy-kernel+unsubscribe@googlegroups.com.
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> > For more options, visit https://groups.google.com/d/optout.

Re: [PATCH] staging: ade7754: Replace mlock with buf_lock and refactor code

[Jonathan Cameron]

On 20/03/17 07:39, Gargi Sharma wrote:
> The IIO subsystem is redefining iio_dev->mlock to be used by
> the IIO core only for protecting device operating mode changes.
> ie. Changes between INDIO_DIRECT_MODE, INDIO_BUFFER_* modes.
> 
> In this driver, mlock was being used to protect hardware state
> changes. Replace it with buf_lock in the devices global data.
> 
> As buf_lock already protects operations in ade7754_write_frequency,
> there isn't a need to acquire the lock inside ade7754_spi_write_reg_8
> when writing to the register.
> 
> Signed-off-by: Gargi Sharma <gs051095@gmail.com>
Question inline.
> ---
>  drivers/staging/iio/meter/ade7754.c | 13 +++++++++++--
>  1 file changed, 11 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/staging/iio/meter/ade7754.c b/drivers/staging/iio/meter/ade7754.c
> index 024463a..eb03469 100644
> --- a/drivers/staging/iio/meter/ade7754.c
> +++ b/drivers/staging/iio/meter/ade7754.c
> @@ -29,6 +29,15 @@ static int ade7754_spi_write_reg_8(struct device *dev, u8 reg_address, u8 val)
>  	struct iio_dev *indio_dev = dev_to_iio_dev(dev);
>  	struct ade7754_state *st = iio_priv(indio_dev);
>  
> +	if (reg_address == ADE7754_WAVMODE) {
> +		st->tx[0] = ADE7754_WRITE_REG(reg_address);
> +		st->tx[1] = val;
> +
> +		ret = spi_write(st->us, st->tx, 2);
> +
> +		return ret;
> +	}
This block doesn't fit with the description.  What's going on here?
> +
>  	mutex_lock(&st->buf_lock);
>  	st->tx[0] = ADE7754_WRITE_REG(reg_address);
>  	st->tx[1] = val;
> @@ -430,7 +439,7 @@ static ssize_t ade7754_write_frequency(struct device *dev,
>  	if (!val)
>  		return -EINVAL;
>  
> -	mutex_lock(&indio_dev->mlock);
> +	mutex_lock(&st->buf_lock);
>  
>  	t = 26000 / val;
>  	if (t > 0)
> @@ -451,7 +460,7 @@ static ssize_t ade7754_write_frequency(struct device *dev,
>  	ret = ade7754_spi_write_reg_8(dev, ADE7754_WAVMODE, reg);
>  
>  out:
> -	mutex_unlock(&indio_dev->mlock);
> +	mutex_unlock(&st->buf_lock);
>  
>  	return ret ? ret : len;
>  }
> 

Re: [PATCH] staging: ade7754: Replace mlock with buf_lock and refactor code

[Gargi Sharma]

On Wed, Mar 22, 2017 at 1:15 AM, Jonathan Cameron <jic23@kernel.org> wrote:
> On 20/03/17 07:39, Gargi Sharma wrote:
>> The IIO subsystem is redefining iio_dev->mlock to be used by
>> the IIO core only for protecting device operating mode changes.
>> ie. Changes between INDIO_DIRECT_MODE, INDIO_BUFFER_* modes.
>>
>> In this driver, mlock was being used to protect hardware state
>> changes. Replace it with buf_lock in the devices global data.
>>
>> As buf_lock already protects operations in ade7754_write_frequency,
>> there isn't a need to acquire the lock inside ade7754_spi_write_reg_8
>> when writing to the register.
>>
>> Signed-off-by: Gargi Sharma <gs051095@gmail.com>
> Question inline.
>> ---
>>  drivers/staging/iio/meter/ade7754.c | 13 +++++++++++--
>>  1 file changed, 11 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/staging/iio/meter/ade7754.c b/drivers/staging/iio/m=
eter/ade7754.c
>> index 024463a..eb03469 100644
>> --- a/drivers/staging/iio/meter/ade7754.c
>> +++ b/drivers/staging/iio/meter/ade7754.c
>> @@ -29,6 +29,15 @@ static int ade7754_spi_write_reg_8(struct device *dev=
, u8 reg_address, u8 val)
>>       struct iio_dev *indio_dev =3D dev_to_iio_dev(dev);
>>       struct ade7754_state *st =3D iio_priv(indio_dev);
>>
>> +     if (reg_address =3D=3D ADE7754_WAVMODE) {
>> +             st->tx[0] =3D ADE7754_WRITE_REG(reg_address);
>> +             st->tx[1] =3D val;
>> +
>> +             ret =3D spi_write(st->us, st->tx, 2);
>> +
>> +             return ret;
>> +     }

> This block doesn't fit with the description.  What's going on here?

When the function ade_spi_write_reg_8() is called inside
ade7754_write_frequency(), we are writing to this( ADE7754_WAVMODE)
register. When writing to this register we don=E2=80=99t need to hold the
buf_lock since ade7754_write_frequency() already takes care of that.
This block of code does not use the buf_lock since that is taken care
of by ade7754_write_frequency().

Gargi
>> +
>>       mutex_lock(&st->buf_lock);
>>       st->tx[0] =3D ADE7754_WRITE_REG(reg_address);
>>       st->tx[1] =3D val;
>> @@ -430,7 +439,7 @@ static ssize_t ade7754_write_frequency(struct device=
 *dev,
>>       if (!val)
>>               return -EINVAL;
>>
>> -     mutex_lock(&indio_dev->mlock);
>> +     mutex_lock(&st->buf_lock);
>>
>>       t =3D 26000 / val;
>>       if (t > 0)
>> @@ -451,7 +460,7 @@ static ssize_t ade7754_write_frequency(struct device=
 *dev,
>>       ret =3D ade7754_spi_write_reg_8(dev, ADE7754_WAVMODE, reg);
>>
>>  out:
>> -     mutex_unlock(&indio_dev->mlock);
>> +     mutex_unlock(&st->buf_lock);
>>
>>       return ret ? ret : len;
>>  }
>>
>

Re: [PATCH] staging: ade7754: Replace mlock with buf_lock and refactor code

[Gargi Sharma]

On Wed, Mar 22, 2017 at 1:15 AM, Jonathan Cameron <jic23@kernel.org> wrote:
> On 20/03/17 07:39, Gargi Sharma wrote:
>> The IIO subsystem is redefining iio_dev->mlock to be used by
>> the IIO core only for protecting device operating mode changes.
>> ie. Changes between INDIO_DIRECT_MODE, INDIO_BUFFER_* modes.
>>
>> In this driver, mlock was being used to protect hardware state
>> changes. Replace it with buf_lock in the devices global data.
>>
>> As buf_lock already protects operations in ade7754_write_frequency,
>> there isn't a need to acquire the lock inside ade7754_spi_write_reg_8
>> when writing to the register.
>>
>> Signed-off-by: Gargi Sharma <gs051095@gmail.com>
> Question inline.
>> ---
>>  drivers/staging/iio/meter/ade7754.c | 13 +++++++++++--
>>  1 file changed, 11 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/staging/iio/meter/ade7754.c b/drivers/staging/iio/meter/ade7754.c
>> index 024463a..eb03469 100644
>> --- a/drivers/staging/iio/meter/ade7754.c
>> +++ b/drivers/staging/iio/meter/ade7754.c
>> @@ -29,6 +29,15 @@ static int ade7754_spi_write_reg_8(struct device *dev, u8 reg_address, u8 val)
>>       struct iio_dev *indio_dev = dev_to_iio_dev(dev);
>>       struct ade7754_state *st = iio_priv(indio_dev);
>>
>> +     if (reg_address == ADE7754_WAVMODE) {
>> +             st->tx[0] = ADE7754_WRITE_REG(reg_address);
>> +             st->tx[1] = val;
>> +
>> +             ret = spi_write(st->us, st->tx, 2);
>> +
>> +             return ret;
>> +     }

> This block doesn't fit with the description.  What's going on here?

When the function ade_spi_write_reg_8() is called inside
ade7754_write_frequency(), we are writing to this( ADE7754_WAVMODE)
register. When writing to this register we don’t need to hold the
buf_lock since ade7754_write_frequency() already takes care of that.
This block of code does not use the buf_lock since that is taken care
of by ade7754_write_frequency().

Gargi
>> +
>>       mutex_lock(&st->buf_lock);
>>       st->tx[0] = ADE7754_WRITE_REG(reg_address);
>>       st->tx[1] = val;
>> @@ -430,7 +439,7 @@ static ssize_t ade7754_write_frequency(struct device *dev,
>>       if (!val)
>>               return -EINVAL;
>>
>> -     mutex_lock(&indio_dev->mlock);
>> +     mutex_lock(&st->buf_lock);
>>
>>       t = 26000 / val;
>>       if (t > 0)
>> @@ -451,7 +460,7 @@ static ssize_t ade7754_write_frequency(struct device *dev,
>>       ret = ade7754_spi_write_reg_8(dev, ADE7754_WAVMODE, reg);
>>
>>  out:
>> -     mutex_unlock(&indio_dev->mlock);
>> +     mutex_unlock(&st->buf_lock);
>>
>>       return ret ? ret : len;
>>  }
>>
>

Re: [Outreachy kernel] [PATCH] staging: ade7754: Replace mlock with buf_lock and refactor code

[Alison Schofield]

On Tue, Mar 21, 2017 at 11:48:27PM +0530, Gargi Sharma wrote:
> On Tue, Mar 21, 2017 at 11:42 PM, Alison Schofield <amsfield22@gmail.com> wrote:
> > On Tue, Mar 21, 2017 at 11:18:23PM +0530, Gargi Sharma wrote:
> >> On Tue, Mar 21, 2017 at 10:54 PM, Alison Schofield <amsfield22@gmail.com> wrote:
> >> > On Mon, Mar 20, 2017 at 01:09:21PM +0530, Gargi Sharma wrote:
> >> >> The IIO subsystem is redefining iio_dev->mlock to be used by
> >> >> the IIO core only for protecting device operating mode changes.
> >> >> ie. Changes between INDIO_DIRECT_MODE, INDIO_BUFFER_* modes.
> >> >>
> >> >> In this driver, mlock was being used to protect hardware state
> >> >> changes. Replace it with buf_lock in the devices global data.
> >> >>
> >> >> As buf_lock already protects operations in ade7754_write_frequency,
> >> >> there isn't a need to acquire the lock inside ade7754_spi_write_reg_8
> >> >> when writing to the register.
> >> >
> >> > Hi Gargi,
> >> >
> >> > Looks like something went wrong in your patch below.  It doesn't do what
> >> > you say it'll do...Instead of removing the lock from _write_reg_8()
> >> > it inserts a bunch of code.  Anyway, it seems that w_rite_reg_8() is used
> >> > in multiple places, so removing that lock doesn't appear to be an
> >> > option.
> >> >
> >> > See below...
> >> >
> >> > alisons
> >> >
> >> >>
> >> >> Signed-off-by: Gargi Sharma <gs051095@gmail.com>
> >> >> ---
> >> >>  drivers/staging/iio/meter/ade7754.c | 13 +++++++++++--
> >> >>  1 file changed, 11 insertions(+), 2 deletions(-)
> >> >>
> >> >> diff --git a/drivers/staging/iio/meter/ade7754.c b/drivers/staging/iio/meter/ade7754.c
> >> >> index 024463a..eb03469 100644
> >> >> --- a/drivers/staging/iio/meter/ade7754.c
> >> >> +++ b/drivers/staging/iio/meter/ade7754.c
> >> >> @@ -29,6 +29,15 @@ static int ade7754_spi_write_reg_8(struct device *dev, u8 reg_address, u8 val)
> >> >>       struct iio_dev *indio_dev = dev_to_iio_dev(dev);
> >> >>       struct ade7754_state *st = iio_priv(indio_dev);
> >> >>
> >> >> +     if (reg_address == ADE7754_WAVMODE) {
> >> >> +             st->tx[0] = ADE7754_WRITE_REG(reg_address);
> >> >> +             st->tx[1] = val;
> >> >> +
> >> >> +             ret = spi_write(st->us, st->tx, 2);
> >> >> +
> >> >> +             return ret;
> >> >> +     }
> >> >> +
> >> > What's this?
> >>
> >> When the function ade_spi_write_reg_8() is called inside
> >> ade7754_write_frequency(), we are writing to this( ADE7754_WAVMODE)
> >> register. When writing to this register we don't need to hold the
> >> buf_lock since ade7754_write_frequency() already takes care of that.
> >
> > Oh! I see it now. You created a special 'no lock needed' case
> > inside of --write_reg_8 for  writing frequency.   That works,
> > but it's...ummm...sneaky ;)  Let's see if there's another way.
> >
> > Look back at Lars suggestion on a similar patch.  Maybe that
> > will apply here.
> > http://marc.info/?l=linux-kernel&m=148940648615743&w=2
> >
> 
> I did look at the patch you suggested for inspiration :) What I could
> not understand was the part where Lars wrote about "doing a
> read-modify-write cycle in a protected section." I can write a
> separate function for --write_reg_8 that does not take the lock, but
> do not know how to do a "read-modify-write cycle in a protected
> section" :(
> 
> Gargi

Hi Gargi,
The mlock wasn't really protecting the read followed by write.
You'll introduce a new func that does that.  It'll use the
existing transaction lock so that an spi_write can't sneak
in between your spi_read and write.  

This is going to be the same change in all the meter drivers.
3 are exactly the same,  a 4th is very close.  

alisons









> > alisons
> >
> >
> >>
> >> >
> >> >>       mutex_lock(&st->buf_lock);
> >> >>       st->tx[0] = ADE7754_WRITE_REG(reg_address);
> >> >>       st->tx[1] = val;
> >> >> @@ -430,7 +439,7 @@ static ssize_t ade7754_write_frequency(struct device *dev,
> >> >>       if (!val)
> >> >>               return -EINVAL;
> >> >>
> >> >> -     mutex_lock(&indio_dev->mlock);
> >> >> +     mutex_lock(&st->buf_lock);
> >> >>
> >> >>       t = 26000 / val;
> >> >>       if (t > 0)
> >> >> @@ -451,7 +460,7 @@ static ssize_t ade7754_write_frequency(struct device *dev,
> >> >>       ret = ade7754_spi_write_reg_8(dev, ADE7754_WAVMODE, reg);
> >> >>
> >> >>  out:
> >> >> -     mutex_unlock(&indio_dev->mlock);
> >> >> +     mutex_unlock(&st->buf_lock);
> >> >>
> >> >>       return ret ? ret : len;
> >> >>  }
> >>
> >> The buf_lock inside ade7754_write_frequency() takes into account that
> >> when using the function ade7754_spi_write_reg_8, lock is already held
> >> and locking is no longer required inside the ade7754_spi_write_reg_8()
> >> function.
> >>
> >> Let me know if this sounds okay, I can perhaps edit the commit log to
> >> make this clearer.
> >>
> >> Thanks,
> >> Gargi
> >>
> >> >> --
> >> >> 2.7.4
> >> >>
> >> >> --
> >> >> You received this message because you are subscribed to the Google Groups "outreachy-kernel" group.
> >> >> To unsubscribe from this group and stop receiving emails from it, send an email to outreachy-kernel+unsubscribe@googlegroups.com.
> >> >> To post to this group, send email to outreachy-kernel@googlegroups.com.
> >> >> To view this discussion on the web visit https://groups.google.com/d/msgid/outreachy-kernel/1489995561-6988-1-git-send-email-gs051095%40gmail.com.
> >> >> For more options, visit https://groups.google.com/d/optout.
> >> >
> >> > --
> >> > You received this message because you are subscribed to the Google Groups "outreachy-kernel" group.
> >> > To unsubscribe from this group and stop receiving emails from it, send an email to outreachy-kernel+unsubscribe@googlegroups.com.
> >> > To post to this group, send email to outreachy-kernel@googlegroups.com.
> >> > To view this discussion on the web visit https://groups.google.com/d/msgid/outreachy-kernel/20170321172438.GC2793%40d830.WORKGROUP.
> >> > For more options, visit https://groups.google.com/d/optout.
> >
> > --
> > You received this message because you are subscribed to the Google Groups "outreachy-kernel" group.
> > To unsubscribe from this group and stop receiving emails from it, send an email to outreachy-kernel+unsubscribe@googlegroups.com.
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> > To view this discussion on the web visit https://groups.google.com/d/msgid/outreachy-kernel/20170321181207.GA10699%40d830.WORKGROUP.
> > For more options, visit https://groups.google.com/d/optout.

Re: [PATCH] staging: ade7754: Replace mlock with buf_lock and refactor code

[Jonathan Cameron]

On 21/03/17 19:52, Gargi Sharma wrote:
> On Wed, Mar 22, 2017 at 1:15 AM, Jonathan Cameron <jic23@kernel.org> wrote:
>> On 20/03/17 07:39, Gargi Sharma wrote:
>>> The IIO subsystem is redefining iio_dev->mlock to be used by
>>> the IIO core only for protecting device operating mode changes.
>>> ie. Changes between INDIO_DIRECT_MODE, INDIO_BUFFER_* modes.
>>>
>>> In this driver, mlock was being used to protect hardware state
>>> changes. Replace it with buf_lock in the devices global data.
>>>
>>> As buf_lock already protects operations in ade7754_write_frequency,
>>> there isn't a need to acquire the lock inside ade7754_spi_write_reg_8
>>> when writing to the register.
>>>
>>> Signed-off-by: Gargi Sharma <gs051095@gmail.com>
>> Question inline.
>>> ---
>>>  drivers/staging/iio/meter/ade7754.c | 13 +++++++++++--
>>>  1 file changed, 11 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/staging/iio/meter/ade7754.c b/drivers/staging/iio/meter/ade7754.c
>>> index 024463a..eb03469 100644
>>> --- a/drivers/staging/iio/meter/ade7754.c
>>> +++ b/drivers/staging/iio/meter/ade7754.c
>>> @@ -29,6 +29,15 @@ static int ade7754_spi_write_reg_8(struct device *dev, u8 reg_address, u8 val)
>>>       struct iio_dev *indio_dev = dev_to_iio_dev(dev);
>>>       struct ade7754_state *st = iio_priv(indio_dev);
>>>
>>> +     if (reg_address == ADE7754_WAVMODE) {
>>> +             st->tx[0] = ADE7754_WRITE_REG(reg_address);
>>> +             st->tx[1] = val;
>>> +
>>> +             ret = spi_write(st->us, st->tx, 2);
>>> +
>>> +             return ret;
>>> +     }
> 
>> This block doesn't fit with the description.  What's going on here?
> 
> When the function ade_spi_write_reg_8() is called inside
> ade7754_write_frequency(), we are writing to this( ADE7754_WAVMODE)
> register. When writing to this register we don’t need to hold the
> buf_lock since ade7754_write_frequency() already takes care of that.
> This block of code does not use the buf_lock since that is taken care
> of by ade7754_write_frequency().
This strikes me as a very fragile way of coding this.

Also, unless I'm missing something, the lock taken there is still mlock...
> 
> Gargi
>>> +
>>>       mutex_lock(&st->buf_lock);
>>>       st->tx[0] = ADE7754_WRITE_REG(reg_address);
>>>       st->tx[1] = val;
>>> @@ -430,7 +439,7 @@ static ssize_t ade7754_write_frequency(struct device *dev,
>>>       if (!val)
>>>               return -EINVAL;
>>>
>>> -     mutex_lock(&indio_dev->mlock);
>>> +     mutex_lock(&st->buf_lock);
>>>
>>>       t = 26000 / val;
>>>       if (t > 0)
>>> @@ -451,7 +460,7 @@ static ssize_t ade7754_write_frequency(struct device *dev,
>>>       ret = ade7754_spi_write_reg_8(dev, ADE7754_WAVMODE, reg);
>>>
>>>  out:
>>> -     mutex_unlock(&indio_dev->mlock);
>>> +     mutex_unlock(&st->buf_lock);
>>>
>>>       return ret ? ret : len;
>>>  }
>>>
>>
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