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

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Message-ID: <aK68qXqStIwBrejF@stanley.mountain>
Date: Wed, 27 Aug 2025 11:07:05 +0300
From: Dan Carpenter <dan.carpenter@...aro.org>
To: Osama Abdelkader <osama.abdelkader@...il.com>
Cc: gregkh@...uxfoundation.org, dpenkler@...il.com,
	matchstick@...erthere.org, arnd@...db.de,
	linux-kernel@...r.kernel.org, linux-staging@...ts.linux.dev
Subject: Re: [PATCH] staging: gpib: simplify and fix get_data_lines

On Wed, Aug 27, 2025 at 10:15:33AM +0300, Dan Carpenter wrote:
> On Wed, Aug 27, 2025 at 12:05:02AM +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.
> 
> Using the last bit in an error code is not really "error handling"...
> 
> What you could do instead would be something like:
> 
> 	int ret;
> 
> 	for (i = 0; i < 8; i++) {
> 		ret |= (gpiod_get_value(lines[i]) & 1) << i;
> 		if (ret < 0) {
> 			pr_err("something failed\n");
> 			return -EINVAL;

I meant to write "return 0;".  It's type u8.

Also that doesn't work.  The masks and shift mess it up.

	u8 val = 0;
	int ret;

	for (i = 0; i < 8; i++) {
		ret = gpiod_get_value(lines[i]);
		if (ret < 0) {
			pr_err("something failed\n");
			continue;
		}
		val |= ret << i;
	}

	return ~val;

regards,
dan carpenter