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Wed, 27 Aug 2025 01:07:11 -0700 (PDT) Date: Wed, 27 Aug 2025 11:07:05 +0300 From: Dan Carpenter To: Osama Abdelkader Cc: gregkh@linuxfoundation.org, dpenkler@gmail.com, matchstick@neverthere.org, arnd@arndb.de, linux-kernel@vger.kernel.org, linux-staging@lists.linux.dev Subject: Re: [PATCH] staging: gpib: simplify and fix get_data_lines Message-ID: References: <20250826220502.210485-1-osama.abdelkader@gmail.com> Precedence: bulk X-Mailing-List: linux-staging@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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