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Date:   Mon, 20 Feb 2017 17:36:52 +0000
From:   Ian Abbott <abbotti@....co.uk>
To:     Cheah Kok Cheong <thrust73@...il.com>
Cc:     hsweeten@...ionengravers.com, gregkh@...uxfoundation.org,
        devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org
Subject: 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@...il.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@....co.uk> )=-
-=(                          Web: http://www.mev.co.uk/  )=-

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