linux-kernel - Re: [PATCH v2] staging: gpib: simplify and fix get_data

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Message-ID: <aK8SGpevZsGM5CCF@egonzo>
Date: Wed, 27 Aug 2025 16:11:38 +0200
From: Dave Penkler <dpenkler@...il.com>
To: Dan Carpenter <dan.carpenter@...aro.org>
Cc: Osama Abdelkader <osama.abdelkader@...il.com>,
	gregkh@...uxfoundation.org, matchstick@...erthere.org,
	arnd@...db.de, linux-kernel@...r.kernel.org,
	linux-staging@...ts.linux.dev, marcello.carla@....com
Subject: Re: [PATCH v2] staging: gpib: simplify and fix get_data_lines

On Wed, Aug 27, 2025 at 03:16:28PM +0300, Dan Carpenter wrote:
> On Wed, Aug 27, 2025 at 01:38:57PM +0200, Osama Abdelkader wrote:
> > The function `get_data_lines()` in gpib_bitbang.c currently reads 8
> > GPIO descriptors individually and combines them into a byte.
> > This has two issues:
> > 
> >   * `gpiod_get_value()` returns an `int` which may be negative on
> >     error. Assigning it directly into a `u8` may propagate unexpected
> >     values. Masking ensures only the LSB is used.
> 
> This part isn't really true any more.
> 
> >   * The code is repetitive and harder to extend.
> > 
> > Fix this by introducing a local array of GPIO descriptors and looping
> > over them, while masking the return value to its least significant bit.
> 
> There really isn't any need to mask now that we're checking for
> negatives.
> 
> > 
> > This reduces duplication, makes the code more maintainable, and avoids
> > possible data corruption from negative `gpiod_get_value()` returns.
> > 
> > Signed-off-by: Osama Abdelkader <osama.abdelkader@...il.com>
> > ---
> > v2:
> > Just print the gpio pin error and leave the bit as zero
> > ---
> >  drivers/staging/gpib/gpio/gpib_bitbang.c | 28 ++++++++++++++----------
> >  1 file changed, 17 insertions(+), 11 deletions(-)
> > 
> > diff --git a/drivers/staging/gpib/gpio/gpib_bitbang.c b/drivers/staging/gpib/gpio/gpib_bitbang.c
> > index 17884810fd69..f4ca59c007dd 100644
> > --- a/drivers/staging/gpib/gpio/gpib_bitbang.c
> > +++ b/drivers/staging/gpib/gpio/gpib_bitbang.c
> > @@ -1403,17 +1403,23 @@ static void set_data_lines(u8 byte)
> >  
> >  static u8 get_data_lines(void)
> >  {
> > -	u8 ret;
> > -
> > -	ret = gpiod_get_value(D01);
> > -	ret |= gpiod_get_value(D02) << 1;
> > -	ret |= gpiod_get_value(D03) << 2;
> > -	ret |= gpiod_get_value(D04) << 3;
> > -	ret |= gpiod_get_value(D05) << 4;
> > -	ret |= gpiod_get_value(D06) << 5;
> > -	ret |= gpiod_get_value(D07) << 6;
> > -	ret |= gpiod_get_value(D08) << 7;
> > -	return ~ret;
> > +	struct gpio_desc *lines[8] = {
> > +		D01, D02, D03, D04, D05, D06, D07, D08
> > +	};
> > +
> 
> Delete this blank line.
> 
> > +	u8 val = 0;
> > +	int ret, i;
> > +
> > +	for (i = 0; i < 8; i++) {
> > +		ret = gpiod_get_value(lines[i]);
> > +		if (ret < 0) {
> > +			pr_err("get GPIO pin %d error: %d\n", i, ret);
> > +			continue;
> > +		}
> > +		val |= (ret & 1) << i;
> 
> Delete the mask.
> 
> (I wavered on whether I should comment on the nit picky things I've
> said in this email, but in the end it was the out of date commit
> message which pushed me over the edge.  I would have ignored the
> other things otherwise).
> 
> regards,
> dan carpenter
> 
> 
This patch seems unnecessary.
The code will never be extended.
In the unlikely case of errors it will produce a huge streams of console spam.
It negatively impacts performance:  114209 bytes/sec vs 118274 bytes/sec.
regards,
-Dave