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[PATCH] Staging: comedi: drivers: comedi_test: Avoid multiple line dereference

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  [PATCH] Staging: comedi: drivers: comedi_test: Avoid multiple line dereference Cheah Kok Cheong <thrust73@gmail.com> - 2017-02-20 09:40 +0100
    Re: [PATCH] Staging: comedi: drivers: comedi_test: Avoid multiple  line dereference Ian Abbott <abbotti@mev.co.uk> - 2017-02-20 11:10 +0100
      Re: [PATCH] Staging: comedi: drivers: comedi_test: Avoid multiple  line dereference Cheah Kok Cheong <thrust73@gmail.com> - 2017-02-20 17:10 +0100
        Re: [PATCH] Staging: comedi: drivers: comedi_test: Avoid multiple  line dereference Ian Abbott <abbotti@mev.co.uk> - 2017-02-20 18:40 +0100
          Re: [PATCH] Staging: comedi: drivers: comedi_test: Avoid multiple  line dereference Cheah Kok Cheong <thrust73@gmail.com> - 2017-02-21 10:40 +0100
            Re: [PATCH] Staging: comedi: drivers: comedi_test: Avoid multiple  line dereference Ian Abbott <abbotti@mev.co.uk> - 2017-02-21 11:20 +0100
              Re: [PATCH] Staging: comedi: drivers: comedi_test: Avoid multiple  line dereference Valentin Rothberg <valentinrothberg@gmail.com> - 2017-02-21 11:30 +0100
                Re: [PATCH] Staging: comedi: drivers: comedi_test: Avoid multiple  line dereference Cheah Kok Cheong <thrust73@gmail.com> - 2017-02-21 17:40 +0100
                  Re: [PATCH] Staging: comedi: drivers: comedi_test: Avoid multiple  line dereference Joe Perches <joe@perches.com> - 2017-02-21 18:30 +0100
                    Re: [PATCH] Staging: comedi: drivers: comedi_test: Avoid multiple  line dereference Valentin Rothberg <valentinrothberg@gmail.com> - 2017-02-22 09:40 +0100

#1584405 — [PATCH] Staging: comedi: drivers: comedi_test: Avoid multiple line dereference

Fix checkpatch warning "Avoid multiple line dereference"
using a local variable to avoid line wrap.

Signed-off-by: Cheah Kok Cheong <thrust73@gmail.com>
---
 drivers/staging/comedi/drivers/comedi_test.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/drivers/staging/comedi/drivers/comedi_test.c b/drivers/staging/comedi/drivers/comedi_test.c
index 2a063f0..fde83e0 100644
--- a/drivers/staging/comedi/drivers/comedi_test.c
+++ b/drivers/staging/comedi/drivers/comedi_test.c
@@ -480,11 +480,9 @@ static void waveform_ao_timer(unsigned long arg)
 			/* output the last scan */
 			for (i = 0; i < cmd->scan_end_arg; i++) {
 				unsigned int chan = CR_CHAN(cmd->chanlist[i]);
+				unsigned short d = devpriv->ao_loopbacks[chan];
 
-				if (comedi_buf_read_samples(s,
-							    &devpriv->
-							     ao_loopbacks[chan],
-							    1) == 0) {
+				if (!comedi_buf_read_samples(s, &d, 1)) {
 					/* unexpected underrun! (cancelled?) */
 					async->events |= COMEDI_CB_OVERFLOW;
 					goto underrun;
-- 
2.7.4

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#1584463 — Re: [PATCH] Staging: comedi: drivers: comedi_test: Avoid multiple line dereference

On 20/02/17 08:28, Cheah Kok Cheong wrote:
> Fix checkpatch warning "Avoid multiple line dereference"
> using a local variable to avoid line wrap.
>
> Signed-off-by: Cheah Kok Cheong <thrust73@gmail.com>
> ---
>  drivers/staging/comedi/drivers/comedi_test.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/staging/comedi/drivers/comedi_test.c b/drivers/staging/comedi/drivers/comedi_test.c
> index 2a063f0..fde83e0 100644
> --- a/drivers/staging/comedi/drivers/comedi_test.c
> +++ b/drivers/staging/comedi/drivers/comedi_test.c
> @@ -480,11 +480,9 @@ static void waveform_ao_timer(unsigned long arg)
>  			/* output the last scan */
>  			for (i = 0; i < cmd->scan_end_arg; i++) {
>  				unsigned int chan = CR_CHAN(cmd->chanlist[i]);
> +				unsigned short d = devpriv->ao_loopbacks[chan];
>
> -				if (comedi_buf_read_samples(s,
> -							    &devpriv->
> -							     ao_loopbacks[chan],
> -							    1) == 0) {
> +				if (!comedi_buf_read_samples(s, &d, 1)) {
>  					/* unexpected underrun! (cancelled?) */
>  					async->events |= COMEDI_CB_OVERFLOW;
>  					goto underrun;
>

NAK.  This leaves devpriv->ao_loopbacks[chan] unchanged.

-- 
-=( Ian Abbott @ MEV Ltd.    E-mail: <abbotti@mev.co.uk> )=-
-=(                          Web: http://www.mev.co.uk/  )=-

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#1584701 — Re: [PATCH] Staging: comedi: drivers: comedi_test: Avoid multiple line dereference

On Mon, Feb 20, 2017 at 10:03:39AM +0000, Ian Abbott wrote:
> On 20/02/17 08:28, Cheah Kok Cheong wrote:
> >Fix checkpatch warning "Avoid multiple line dereference"
> >using a local variable to avoid line wrap.
> >
> >Signed-off-by: Cheah Kok Cheong <thrust73@gmail.com>
> >---
> > drivers/staging/comedi/drivers/comedi_test.c | 6 ++----
> > 1 file changed, 2 insertions(+), 4 deletions(-)
> >
> >diff --git a/drivers/staging/comedi/drivers/comedi_test.c b/drivers/staging/comedi/drivers/comedi_test.c
> >index 2a063f0..fde83e0 100644
> >--- a/drivers/staging/comedi/drivers/comedi_test.c
> >+++ b/drivers/staging/comedi/drivers/comedi_test.c
> >@@ -480,11 +480,9 @@ static void waveform_ao_timer(unsigned long arg)
> > 			/* output the last scan */
> > 			for (i = 0; i < cmd->scan_end_arg; i++) {
> > 				unsigned int chan = CR_CHAN(cmd->chanlist[i]);
> >+				unsigned short d = devpriv->ao_loopbacks[chan];
> >
> >-				if (comedi_buf_read_samples(s,
> >-							    &devpriv->
> >-							     ao_loopbacks[chan],
> >-							    1) == 0) {
> >+				if (!comedi_buf_read_samples(s, &d, 1)) {
> > 					/* unexpected underrun! (cancelled?) */
> > 					async->events |= COMEDI_CB_OVERFLOW;
> > 					goto underrun;
> >
> 
> NAK.  This leaves devpriv->ao_loopbacks[chan] unchanged.
> 

Thanks for pointing this out. In that case will assigning the variable to
devpriv->ao_loopbacks[chan] be acceptable? Please review below snippet.

Otherwise I'll just drop the variable and adjust the lines to avoid
checkpatch warning.

Sorry for the inconvenience caused.

[ Snip ]

			/* output the last scan */
			for (i = 0; i < cmd->scan_end_arg; i++) {
				unsigned int chan = CR_CHAN(cmd->chanlist[i]);
				unsigned short data;

				if (!comedi_buf_read_samples(s, &data, 1)) {
					/* unexpected underrun! (cancelled?) */
					async->events |= COMEDI_CB_OVERFLOW;
					goto underrun;
				}

				devpriv->ao_loopbacks[chan] = data;
			}
			/* advance time of last scan */

[ Snip ]

Thks.
Brgds,
CheahKC

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#1584797 — Re: [PATCH] Staging: comedi: drivers: comedi_test: Avoid multiple line dereference

On 20/02/17 16:02, Cheah Kok Cheong wrote:
> On Mon, Feb 20, 2017 at 10:03:39AM +0000, Ian Abbott wrote:
>> On 20/02/17 08:28, Cheah Kok Cheong wrote:
>>> Fix checkpatch warning "Avoid multiple line dereference"
>>> using a local variable to avoid line wrap.
>>>
>>> Signed-off-by: Cheah Kok Cheong <thrust73@gmail.com>
>>> ---
>>> drivers/staging/comedi/drivers/comedi_test.c | 6 ++----
>>> 1 file changed, 2 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/drivers/staging/comedi/drivers/comedi_test.c b/drivers/staging/comedi/drivers/comedi_test.c
>>> index 2a063f0..fde83e0 100644
>>> --- a/drivers/staging/comedi/drivers/comedi_test.c
>>> +++ b/drivers/staging/comedi/drivers/comedi_test.c
>>> @@ -480,11 +480,9 @@ static void waveform_ao_timer(unsigned long arg)
>>> 			/* output the last scan */
>>> 			for (i = 0; i < cmd->scan_end_arg; i++) {
>>> 				unsigned int chan = CR_CHAN(cmd->chanlist[i]);
>>> +				unsigned short d = devpriv->ao_loopbacks[chan];
>>>
>>> -				if (comedi_buf_read_samples(s,
>>> -							    &devpriv->
>>> -							     ao_loopbacks[chan],
>>> -							    1) == 0) {
>>> +				if (!comedi_buf_read_samples(s, &d, 1)) {
>>> 					/* unexpected underrun! (cancelled?) */
>>> 					async->events |= COMEDI_CB_OVERFLOW;
>>> 					goto underrun;
>>>
>>
>> NAK.  This leaves devpriv->ao_loopbacks[chan] unchanged.
>>
>
> Thanks for pointing this out. In that case will assigning the variable to
> devpriv->ao_loopbacks[chan] be acceptable? Please review below snippet.
>
> Otherwise I'll just drop the variable and adjust the lines to avoid
> checkpatch warning.
>
> Sorry for the inconvenience caused.
>
> [ Snip ]
>
> 			/* output the last scan */
> 			for (i = 0; i < cmd->scan_end_arg; i++) {
> 				unsigned int chan = CR_CHAN(cmd->chanlist[i]);
> 				unsigned short data;
>
> 				if (!comedi_buf_read_samples(s, &data, 1)) {
> 					/* unexpected underrun! (cancelled?) */
> 					async->events |= COMEDI_CB_OVERFLOW;
> 					goto underrun;
> 				}
>
> 				devpriv->ao_loopbacks[chan] = data;
> 			}
> 			/* advance time of last scan */
>
> [ Snip ]

It will work, but you could just use a pointer variable set to 
&devpriv->ao_loopbacks[chan] and pass that to comedi_buf_read_samples().

-- 
-=( Ian Abbott @ MEV Ltd.    E-mail: <abbotti@mev.co.uk> )=-
-=(                          Web: http://www.mev.co.uk/  )=-

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#1585164 — Re: [PATCH] Staging: comedi: drivers: comedi_test: Avoid multiple line dereference

On Mon, Feb 20, 2017 at 05:36:52PM +0000, Ian Abbott wrote:
> On 20/02/17 16:02, Cheah Kok Cheong wrote:
> >On Mon, Feb 20, 2017 at 10:03:39AM +0000, Ian Abbott wrote:
> >>On 20/02/17 08:28, Cheah Kok Cheong wrote:
> >>>Fix checkpatch warning "Avoid multiple line dereference"
> >>>using a local variable to avoid line wrap.
> >>>
> >>>Signed-off-by: Cheah Kok Cheong <thrust73@gmail.com>
> >>>---
> >>>drivers/staging/comedi/drivers/comedi_test.c | 6 ++----
> >>>1 file changed, 2 insertions(+), 4 deletions(-)
> >>>
> >>>diff --git a/drivers/staging/comedi/drivers/comedi_test.c b/drivers/staging/comedi/drivers/comedi_test.c
> >>>index 2a063f0..fde83e0 100644
> >>>--- a/drivers/staging/comedi/drivers/comedi_test.c
> >>>+++ b/drivers/staging/comedi/drivers/comedi_test.c
> >>>@@ -480,11 +480,9 @@ static void waveform_ao_timer(unsigned long arg)
> >>>			/* output the last scan */
> >>>			for (i = 0; i < cmd->scan_end_arg; i++) {
> >>>				unsigned int chan = CR_CHAN(cmd->chanlist[i]);
> >>>+				unsigned short d = devpriv->ao_loopbacks[chan];
> >>>
> >>>-				if (comedi_buf_read_samples(s,
> >>>-							    &devpriv->
> >>>-							     ao_loopbacks[chan],
> >>>-							    1) == 0) {
> >>>+				if (!comedi_buf_read_samples(s, &d, 1)) {
> >>>					/* unexpected underrun! (cancelled?) */
> >>>					async->events |= COMEDI_CB_OVERFLOW;
> >>>					goto underrun;
> >>>
> >>
> >>NAK.  This leaves devpriv->ao_loopbacks[chan] unchanged.
> >>
> >
> >Thanks for pointing this out. In that case will assigning the variable to
> >devpriv->ao_loopbacks[chan] be acceptable? Please review below snippet.
> >
> >Otherwise I'll just drop the variable and adjust the lines to avoid
> >checkpatch warning.
> >
> >Sorry for the inconvenience caused.
> >
> >[ Snip ]
> >
> >			/* output the last scan */
> >			for (i = 0; i < cmd->scan_end_arg; i++) {
> >				unsigned int chan = CR_CHAN(cmd->chanlist[i]);
> >				unsigned short data;
> >
> >				if (!comedi_buf_read_samples(s, &data, 1)) {
> >					/* unexpected underrun! (cancelled?) */
> >					async->events |= COMEDI_CB_OVERFLOW;
> >					goto underrun;
> >				}
> >
> >				devpriv->ao_loopbacks[chan] = data;
> >			}
> >			/* advance time of last scan */
> >
> >[ Snip ]
> 
> It will work, but you could just use a pointer variable set to
> &devpriv->ao_loopbacks[chan] and pass that to comedi_buf_read_samples().
> 

Thanks for the suggestion. I tried below snippet 1 with the shortest pointer
name but 80 characters is exceeded. The declaration and initialisation
will have to be splitted. Will this be acceptable or am I doing it wrong
again?

Sorry for the trouble.

Snippet 1:
[ Snip ]

			/* output the last scan */
			for (i = 0; i < cmd->scan_end_arg; i++) {
				unsigned int chan = CR_CHAN(cmd->chanlist[i]);
				unsigned short *p = &devpriv->ao_loopbacks[chan];

				if (!comedi_buf_read_samples(s, p, 1)) {
					/* unexpected underrun! (cancelled?) */
					async->events |= COMEDI_CB_OVERFLOW;
					goto underrun;
				}
			}
			/* advance time of last scan */

[ Snip ]

Snippet 2:
[ Snip ]

			/* output the last scan */
			for (i = 0; i < cmd->scan_end_arg; i++) {
				unsigned int chan = CR_CHAN(cmd->chanlist[i]);
				unsigned short *pd;

				pd = &devpriv->ao_loopbacks[chan];

				if (!comedi_buf_read_samples(s, pd, 1)) {
					/* unexpected underrun! (cancelled?) */
					async->events |= COMEDI_CB_OVERFLOW;
					goto underrun;
				}
			}

[ Snip ]

Thks.
Brgds,
CheahKC

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#1585186 — Re: [PATCH] Staging: comedi: drivers: comedi_test: Avoid multiple line dereference

On 21/02/2017 09:33, Cheah Kok Cheong wrote:
> On Mon, Feb 20, 2017 at 05:36:52PM +0000, Ian Abbott wrote:
>> On 20/02/17 16:02, Cheah Kok Cheong wrote:
>>> On Mon, Feb 20, 2017 at 10:03:39AM +0000, Ian Abbott wrote:
>>>> On 20/02/17 08:28, Cheah Kok Cheong wrote:
>>>>> Fix checkpatch warning "Avoid multiple line dereference"
>>>>> using a local variable to avoid line wrap.
>>>>>
>>>>> Signed-off-by: Cheah Kok Cheong <thrust73@gmail.com>
>>>>> ---
>>>>> drivers/staging/comedi/drivers/comedi_test.c | 6 ++----
>>>>> 1 file changed, 2 insertions(+), 4 deletions(-)
>>>>>
>>>>> diff --git a/drivers/staging/comedi/drivers/comedi_test.c b/drivers/staging/comedi/drivers/comedi_test.c
>>>>> index 2a063f0..fde83e0 100644
>>>>> --- a/drivers/staging/comedi/drivers/comedi_test.c
>>>>> +++ b/drivers/staging/comedi/drivers/comedi_test.c
>>>>> @@ -480,11 +480,9 @@ static void waveform_ao_timer(unsigned long arg)
>>>>> 			/* output the last scan */
>>>>> 			for (i = 0; i < cmd->scan_end_arg; i++) {
>>>>> 				unsigned int chan = CR_CHAN(cmd->chanlist[i]);
>>>>> +				unsigned short d = devpriv->ao_loopbacks[chan];
>>>>>
>>>>> -				if (comedi_buf_read_samples(s,
>>>>> -							    &devpriv->
>>>>> -							     ao_loopbacks[chan],
>>>>> -							    1) == 0) {
>>>>> +				if (!comedi_buf_read_samples(s, &d, 1)) {
>>>>> 					/* unexpected underrun! (cancelled?) */
>>>>> 					async->events |= COMEDI_CB_OVERFLOW;
>>>>> 					goto underrun;
>>>>>
>>>>
>>>> NAK.  This leaves devpriv->ao_loopbacks[chan] unchanged.
>>>>
>>>
>>> Thanks for pointing this out. In that case will assigning the variable to
>>> devpriv->ao_loopbacks[chan] be acceptable? Please review below snippet.
>>>
>>> Otherwise I'll just drop the variable and adjust the lines to avoid
>>> checkpatch warning.
>>>
>>> Sorry for the inconvenience caused.
>>>
>>> [ Snip ]
>>>
>>> 			/* output the last scan */
>>> 			for (i = 0; i < cmd->scan_end_arg; i++) {
>>> 				unsigned int chan = CR_CHAN(cmd->chanlist[i]);
>>> 				unsigned short data;
>>>
>>> 				if (!comedi_buf_read_samples(s, &data, 1)) {
>>> 					/* unexpected underrun! (cancelled?) */
>>> 					async->events |= COMEDI_CB_OVERFLOW;
>>> 					goto underrun;
>>> 				}
>>>
>>> 				devpriv->ao_loopbacks[chan] = data;
>>> 			}
>>> 			/* advance time of last scan */
>>>
>>> [ Snip ]
>>
>> It will work, but you could just use a pointer variable set to
>> &devpriv->ao_loopbacks[chan] and pass that to comedi_buf_read_samples().
>>
>
> Thanks for the suggestion. I tried below snippet 1 with the shortest pointer
> name but 80 characters is exceeded. The declaration and initialisation
> will have to be splitted. Will this be acceptable or am I doing it wrong
> again?
>
> Sorry for the trouble.
>
> Snippet 1:
> [ Snip ]
>
> 			/* output the last scan */
> 			for (i = 0; i < cmd->scan_end_arg; i++) {
> 				unsigned int chan = CR_CHAN(cmd->chanlist[i]);
> 				unsigned short *p = &devpriv->ao_loopbacks[chan];
>
> 				if (!comedi_buf_read_samples(s, p, 1)) {
> 					/* unexpected underrun! (cancelled?) */
> 					async->events |= COMEDI_CB_OVERFLOW;
> 					goto underrun;
> 				}
> 			}
> 			/* advance time of last scan */
>
> [ Snip ]
>
> Snippet 2:
> [ Snip ]
>
> 			/* output the last scan */
> 			for (i = 0; i < cmd->scan_end_arg; i++) {
> 				unsigned int chan = CR_CHAN(cmd->chanlist[i]);
> 				unsigned short *pd;
>
> 				pd = &devpriv->ao_loopbacks[chan];
>
> 				if (!comedi_buf_read_samples(s, pd, 1)) {
> 					/* unexpected underrun! (cancelled?) */
> 					async->events |= COMEDI_CB_OVERFLOW;
> 					goto underrun;
> 				}
> 			}
>
> [ Snip ]

Snippet 2 looks fine.  Alternatives are to modify Snippet 1 to split the 
initialization of the pointer variable after the '=', or to shorten the 
the name of the 'chan' variable.

-- 
-=( Ian Abbott @ MEV Ltd.    E-mail: <abbotti@mev.co.uk> )=-
-=(                          Web: http://www.mev.co.uk/  )=-

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#1585194 — Re: [PATCH] Staging: comedi: drivers: comedi_test: Avoid multiple line dereference

On Feb 21 '17 10:12, Ian Abbott wrote:
> On 21/02/2017 09:33, Cheah Kok Cheong wrote:
> > On Mon, Feb 20, 2017 at 05:36:52PM +0000, Ian Abbott wrote:
> > > On 20/02/17 16:02, Cheah Kok Cheong wrote:
> > > > On Mon, Feb 20, 2017 at 10:03:39AM +0000, Ian Abbott wrote:
> > > > > On 20/02/17 08:28, Cheah Kok Cheong wrote:
> > > > > > Fix checkpatch warning "Avoid multiple line dereference"
> > > > > > using a local variable to avoid line wrap.
> > > > > > 
> > > > > > Signed-off-by: Cheah Kok Cheong <thrust73@gmail.com>
> > > > > > ---
> > > > > > drivers/staging/comedi/drivers/comedi_test.c | 6 ++----
> > > > > > 1 file changed, 2 insertions(+), 4 deletions(-)
> > > > > > 
> > > > > > diff --git a/drivers/staging/comedi/drivers/comedi_test.c b/drivers/staging/comedi/drivers/comedi_test.c
> > > > > > index 2a063f0..fde83e0 100644
> > > > > > --- a/drivers/staging/comedi/drivers/comedi_test.c
> > > > > > +++ b/drivers/staging/comedi/drivers/comedi_test.c
> > > > > > @@ -480,11 +480,9 @@ static void waveform_ao_timer(unsigned long arg)
> > > > > > 			/* output the last scan */
> > > > > > 			for (i = 0; i < cmd->scan_end_arg; i++) {
> > > > > > 				unsigned int chan = CR_CHAN(cmd->chanlist[i]);
> > > > > > +				unsigned short d = devpriv->ao_loopbacks[chan];
> > > > > > 
> > > > > > -				if (comedi_buf_read_samples(s,
> > > > > > -							    &devpriv->
> > > > > > -							     ao_loopbacks[chan],
> > > > > > -							    1) == 0) {
> > > > > > +				if (!comedi_buf_read_samples(s, &d, 1)) {
> > > > > > 					/* unexpected underrun! (cancelled?) */
> > > > > > 					async->events |= COMEDI_CB_OVERFLOW;
> > > > > > 					goto underrun;
> > > > > > 
> > > > > 
> > > > > NAK.  This leaves devpriv->ao_loopbacks[chan] unchanged.
> > > > > 
> > > > 
> > > > Thanks for pointing this out. In that case will assigning the variable to
> > > > devpriv->ao_loopbacks[chan] be acceptable? Please review below snippet.
> > > > 
> > > > Otherwise I'll just drop the variable and adjust the lines to avoid
> > > > checkpatch warning.
> > > > 
> > > > Sorry for the inconvenience caused.
> > > > 
> > > > [ Snip ]
> > > > 
> > > > 			/* output the last scan */
> > > > 			for (i = 0; i < cmd->scan_end_arg; i++) {
> > > > 				unsigned int chan = CR_CHAN(cmd->chanlist[i]);
> > > > 				unsigned short data;
> > > > 
> > > > 				if (!comedi_buf_read_samples(s, &data, 1)) {
> > > > 					/* unexpected underrun! (cancelled?) */
> > > > 					async->events |= COMEDI_CB_OVERFLOW;
> > > > 					goto underrun;
> > > > 				}
> > > > 
> > > > 				devpriv->ao_loopbacks[chan] = data;
> > > > 			}
> > > > 			/* advance time of last scan */
> > > > 
> > > > [ Snip ]
> > > 
> > > It will work, but you could just use a pointer variable set to
> > > &devpriv->ao_loopbacks[chan] and pass that to comedi_buf_read_samples().
> > > 
> > 
> > Thanks for the suggestion. I tried below snippet 1 with the shortest pointer
> > name but 80 characters is exceeded. The declaration and initialisation
> > will have to be splitted. Will this be acceptable or am I doing it wrong
> > again?
> > 
> > Sorry for the trouble.
> > 
> > Snippet 1:
> > [ Snip ]
> > 
> > 			/* output the last scan */
> > 			for (i = 0; i < cmd->scan_end_arg; i++) {
> > 				unsigned int chan = CR_CHAN(cmd->chanlist[i]);
> > 				unsigned short *p = &devpriv->ao_loopbacks[chan];
> > 
> > 				if (!comedi_buf_read_samples(s, p, 1)) {
> > 					/* unexpected underrun! (cancelled?) */
> > 					async->events |= COMEDI_CB_OVERFLOW;
> > 					goto underrun;
> > 				}
> > 			}
> > 			/* advance time of last scan */
> > 
> > [ Snip ]
> > 
> > Snippet 2:
> > [ Snip ]
> > 
> > 			/* output the last scan */
> > 			for (i = 0; i < cmd->scan_end_arg; i++) {
> > 				unsigned int chan = CR_CHAN(cmd->chanlist[i]);
> > 				unsigned short *pd;
> > 
> > 				pd = &devpriv->ao_loopbacks[chan];
> > 
> > 				if (!comedi_buf_read_samples(s, pd, 1)) {
> > 					/* unexpected underrun! (cancelled?) */
> > 					async->events |= COMEDI_CB_OVERFLOW;
> > 					goto underrun;
> > 				}
> > 			}
> > 
> > [ Snip ]
> 
> Snippet 2 looks fine.  Alternatives are to modify Snippet 1 to split the
> initialization of the pointer variable after the '=', or to shorten the the
> name of the 'chan' variable.

Another option could be using the typedefs from include/linux/types.h,
e.g. ushort.  However, this might require changing other declarations as
well to keep consistency.

> -- 
> -=( Ian Abbott @ MEV Ltd.    E-mail: <abbotti@mev.co.uk> )=-
> -=(                          Web: http://www.mev.co.uk/  )=-

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#1585516 — Re: [PATCH] Staging: comedi: drivers: comedi_test: Avoid multiple line dereference

On Tue, Feb 21, 2017 at 11:20:08AM +0100, Valentin Rothberg wrote:
> On Feb 21 '17 10:12, Ian Abbott wrote:
> > On 21/02/2017 09:33, Cheah Kok Cheong wrote:
> > > On Mon, Feb 20, 2017 at 05:36:52PM +0000, Ian Abbott wrote:
> > > > On 20/02/17 16:02, Cheah Kok Cheong wrote:
> > > > > On Mon, Feb 20, 2017 at 10:03:39AM +0000, Ian Abbott wrote:
> > > > > > On 20/02/17 08:28, Cheah Kok Cheong wrote:
> > > > > > > Fix checkpatch warning "Avoid multiple line dereference"
> > > > > > > using a local variable to avoid line wrap.
> > > > > > > 
> > > > > > > Signed-off-by: Cheah Kok Cheong <thrust73@gmail.com>
> > > > > > > ---
> > > > > > > drivers/staging/comedi/drivers/comedi_test.c | 6 ++----
> > > > > > > 1 file changed, 2 insertions(+), 4 deletions(-)
> > > > > > > 
> > > > > > > diff --git a/drivers/staging/comedi/drivers/comedi_test.c b/drivers/staging/comedi/drivers/comedi_test.c
> > > > > > > index 2a063f0..fde83e0 100644
> > > > > > > --- a/drivers/staging/comedi/drivers/comedi_test.c
> > > > > > > +++ b/drivers/staging/comedi/drivers/comedi_test.c
> > > > > > > @@ -480,11 +480,9 @@ static void waveform_ao_timer(unsigned long arg)
> > > > > > > 			/* output the last scan */
> > > > > > > 			for (i = 0; i < cmd->scan_end_arg; i++) {
> > > > > > > 				unsigned int chan = CR_CHAN(cmd->chanlist[i]);
> > > > > > > +				unsigned short d = devpriv->ao_loopbacks[chan];
> > > > > > > 
> > > > > > > -				if (comedi_buf_read_samples(s,
> > > > > > > -							    &devpriv->
> > > > > > > -							     ao_loopbacks[chan],
> > > > > > > -							    1) == 0) {
> > > > > > > +				if (!comedi_buf_read_samples(s, &d, 1)) {
> > > > > > > 					/* unexpected underrun! (cancelled?) */
> > > > > > > 					async->events |= COMEDI_CB_OVERFLOW;
> > > > > > > 					goto underrun;
> > > > > > > 
> > > > > > 
> > > > > > NAK.  This leaves devpriv->ao_loopbacks[chan] unchanged.
> > > > > > 
> > > > > 
> > > > > Thanks for pointing this out. In that case will assigning the variable to
> > > > > devpriv->ao_loopbacks[chan] be acceptable? Please review below snippet.
> > > > > 
> > > > > Otherwise I'll just drop the variable and adjust the lines to avoid
> > > > > checkpatch warning.
> > > > > 
> > > > > Sorry for the inconvenience caused.
> > > > > 
> > > > > [ Snip ]
> > > > > 
> > > > > 			/* output the last scan */
> > > > > 			for (i = 0; i < cmd->scan_end_arg; i++) {
> > > > > 				unsigned int chan = CR_CHAN(cmd->chanlist[i]);
> > > > > 				unsigned short data;
> > > > > 
> > > > > 				if (!comedi_buf_read_samples(s, &data, 1)) {
> > > > > 					/* unexpected underrun! (cancelled?) */
> > > > > 					async->events |= COMEDI_CB_OVERFLOW;
> > > > > 					goto underrun;
> > > > > 				}
> > > > > 
> > > > > 				devpriv->ao_loopbacks[chan] = data;
> > > > > 			}
> > > > > 			/* advance time of last scan */
> > > > > 
> > > > > [ Snip ]
> > > > 
> > > > It will work, but you could just use a pointer variable set to
> > > > &devpriv->ao_loopbacks[chan] and pass that to comedi_buf_read_samples().
> > > > 
> > > 
> > > Thanks for the suggestion. I tried below snippet 1 with the shortest pointer
> > > name but 80 characters is exceeded. The declaration and initialisation
> > > will have to be splitted. Will this be acceptable or am I doing it wrong
> > > again?
> > > 
> > > Sorry for the trouble.
> > > 
> > > Snippet 1:
> > > [ Snip ]
> > > 
> > > 			/* output the last scan */
> > > 			for (i = 0; i < cmd->scan_end_arg; i++) {
> > > 				unsigned int chan = CR_CHAN(cmd->chanlist[i]);
> > > 				unsigned short *p = &devpriv->ao_loopbacks[chan];
> > > 
> > > 				if (!comedi_buf_read_samples(s, p, 1)) {
> > > 					/* unexpected underrun! (cancelled?) */
> > > 					async->events |= COMEDI_CB_OVERFLOW;
> > > 					goto underrun;
> > > 				}
> > > 			}
> > > 			/* advance time of last scan */
> > > 
> > > [ Snip ]
> > > 
> > > Snippet 2:
> > > [ Snip ]
> > > 
> > > 			/* output the last scan */
> > > 			for (i = 0; i < cmd->scan_end_arg; i++) {
> > > 				unsigned int chan = CR_CHAN(cmd->chanlist[i]);
> > > 				unsigned short *pd;
> > > 
> > > 				pd = &devpriv->ao_loopbacks[chan];
> > > 
> > > 				if (!comedi_buf_read_samples(s, pd, 1)) {
> > > 					/* unexpected underrun! (cancelled?) */
> > > 					async->events |= COMEDI_CB_OVERFLOW;
> > > 					goto underrun;
> > > 				}
> > > 			}
> > > 
> > > [ Snip ]
> > 
> > Snippet 2 looks fine.  Alternatives are to modify Snippet 1 to split the
> > initialization of the pointer variable after the '=', or to shorten the the
> > name of the 'chan' variable.

I'm tempted to shorten the 'chan' variable but this will break consistency
since it's also use in static int waveform_ai_insn_read() and
static int waveform_ao_insn_write(). I'll send Snippet 2 as V2.

> 
> Another option could be using the typedefs from include/linux/types.h,
> e.g. ushort.  However, this might require changing other declarations as
> well to keep consistency.

Thanks for the idea. I counted seven instances of 'unsigned short'
in this file so it's not viable for our situation.

Thks.
Brgds,
CheahKC

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#1585555 — Re: [PATCH] Staging: comedi: drivers: comedi_test: Avoid multiple line dereference

On Wed, 2017-02-22 at 00:31 +0800, Cheah Kok Cheong wrote:
> > Another option could be using the typedefs from include/linux/types.h,
> > e.g. ushort.  However, this might require changing other declarations as
> > well to keep consistency.
> 
> Thanks for the idea. I counted seven instances of 'unsigned short'
> in this file so it's not viable for our situation.

I believe using ushort is relatively undesirable as
"unsigned short" is preferred ~10:1 in the kernel

$ git grep -w ushort | wc -l
1381
$ git grep -E "\bunsigned\s+short\b" | wc -l
11288

$ git grep --name-only -w "ushort" | wc -l
129
$ git grep --name-only -E "\bunsigned\s+short\b" | wc -l
2497

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#1585988 — Re: [PATCH] Staging: comedi: drivers: comedi_test: Avoid multiple line dereference

On Feb 21 '17 09:22, Joe Perches wrote:
> On Wed, 2017-02-22 at 00:31 +0800, Cheah Kok Cheong wrote:
> > > Another option could be using the typedefs from include/linux/types.h,
> > > e.g. ushort.  However, this might require changing other declarations as
> > > well to keep consistency.
> > 
> > Thanks for the idea. I counted seven instances of 'unsigned short'
> > in this file so it's not viable for our situation.
> 
> I believe using ushort is relatively undesirable as
> "unsigned short" is preferred ~10:1 in the kernel

Wow, that is suprising to me considering the 80 character limit.  Thanks
for pointing this out!

Regards,
 Valentin

> $ git grep -w ushort | wc -l
> 1381
> $ git grep -E "\bunsigned\s+short\b" | wc -l
> 11288
> 
> $ git grep --name-only -w "ushort" | wc -l
> 129
> $ git grep --name-only -E "\bunsigned\s+short\b" | wc -l
> 2497
> 

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