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Date:   Tue, 21 Feb 2017 17:33:33 +0800
From:   Cheah Kok Cheong <thrust73@...il.com>
To:     Ian Abbott <abbotti@....co.uk>
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 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@...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().
> 

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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