From 3d495b084c760bc1439ee32201e80391e2641f82 Mon Sep 17 00:00:00 2001
From: Kaspar Giger <kaspar.giger@chemspeed.com>
Date: Sat, 6 Sep 2025 23:07:35 +0200
Subject: [PATCH] sysfs: retain support even on older kernels

The ioctl-gpio driver was declared a prerequisite of the sysfs-gpio driver. But since on older Linux kernels (earlier than 5.10) the GPIO v2 interface is not yet available. Therefore, the ioctl-gpio driver is not available for such systems. To still support the sysfs access for those make the ioctl-gpio driver independent of the sysfs-gpio driver.

Note: the ioctl-gpio driver is still attempted to load.
---
 gpioioctl/gpio.go  | 11 ++++++++---
 sysfs/gpio.go      |  4 ++--
 sysfs/gpio_test.go |  2 +-
 3 files changed, 11 insertions(+), 6 deletions(-)

diff --git a/gpioioctl/gpio.go b/gpioioctl/gpio.go
index c4bbcaad..bd2119a6 100644
--- a/gpioioctl/gpio.go
+++ b/gpioioctl/gpio.go
@@ -415,7 +415,12 @@ func newGPIOChip(path string) (*GPIOChip, error) {
 		line_info.offset = uint32(line)
 		err := ioctl_gpio_v2_line_info(chip.fd, &line_info)
 		if err != nil {
-			log.Println("newGPIOChip get line info", err)
+			// older kernels don't support the GPIO v2 API. In this case the above syscall returns an EINVAL
+			// error. That's ok, in this case just don't continue accessing this GPIO chip with this interface
+			// any further.
+			if err.Error() == "invalid argument" {
+				return nil, nil
+			}
 			return nil, fmt.Errorf("reading line info: %w", err)
 		}
 		line := newGPIOLine(uint32(line), string(line_info.name[:]), string(line_info.consumer[:]), chip.fd)
@@ -616,9 +621,9 @@ func (d *driverGPIO) Init() (bool, error) {
 	var chip *GPIOChip
 	for _, item := range items {
 		chip, err = newGPIOChip(item)
-		if err == nil {
+		if chip != nil && err == nil {
 			chips = append(chips, chip)
-		} else {
+		} else if err != nil {
 			log.Println("gpioioctl.driverGPIO.Init() Error", err)
 		}
 	}
diff --git a/sysfs/gpio.go b/sysfs/gpio.go
index a776ca89..f33341a1 100644
--- a/sysfs/gpio.go
+++ b/sysfs/gpio.go
@@ -431,11 +431,11 @@ func (d *driverGPIO) String() string {
 }
 
 func (d *driverGPIO) Prerequisites() []string {
-	return []string{"ioctl-gpio"}
+	return nil
 }
 
 func (d *driverGPIO) After() []string {
-	return nil
+	return []string{"ioctl-gpio"}
 }
 
 // Init initializes GPIO sysfs handling code.
diff --git a/sysfs/gpio_test.go b/sysfs/gpio_test.go
index 32e1538d..e8204a05 100644
--- a/sysfs/gpio_test.go
+++ b/sysfs/gpio_test.go
@@ -204,7 +204,7 @@ func TestPin_readInt(t *testing.T) {
 }
 
 func TestGPIODriver(t *testing.T) {
-	if len((&driverGPIO{}).Prerequisites()) != 1 {
+	if len((&driverGPIO{}).Prerequisites()) != 0 {
 		t.Fatal("unexpected GPIO prerequisites")
 	}
 }