[PATCH v2] staging: gpib: simplify and fix get_data_lines

[Osama Abdelkader <osama.abdelkader@gmail.com>]

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.
  * 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.

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@gmail.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
+	};
+
+	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;
+	}
+
+	return ~val;
 }
 
 static void set_data_lines_input(void)
-- 
2.43.0