cmd: gpio: Add gpio read subcommand

As explained in commit 4af2a33 ("cmd: gpio: Make `gpio input`
return pin value again") the `gpio input` is used in scripts to obtain
the value of a pin, despite the fact that CMD_RET_FAILURE is
indistinguishable from a valid pin value.
To be able to detect failures and properly use the value of a GPIO in
scripts we introduce the `gpio read` command that sets the variable
`name` to the value of the pin. Return code of the `gpio read` command
can be used to check for CMD_RET_SUCCESS or CMD_RET_FAILURE.
CONFIG_CMD_GPIO_READ is used to enable the `gpio read` command.

Signed-off-by: Diego Rondini <diego.rondini@kynetics.com>

cmd/Kconfig

@@ -996,6 +996,13 @@ config CMD_GPIO
 	help
 	  GPIO support.
 
+config CMD_GPIO_READ
+	bool "gpio read - save GPIO value to variable"
+	depends on CMD_GPIO
+	help
+	  Enables the 'gpio read' command that saves the value
+	  of a GPIO pin to a variable.
+
 config CMD_PWM
 	bool "pwm"
 	depends on DM_PWM

cmd/gpio.c

@@ -12,6 +12,9 @@
 #include <dm.h>
 #include <log.h>
 #include <malloc.h>
+#ifdef CONFIG_CMD_GPIO_READ
+#include <env.h>
+#endif
 #include <asm/gpio.h>
 #include <linux/err.h>
 
@@ -25,6 +28,9 @@ enum gpio_cmd {
 	GPIOC_SET,
 	GPIOC_CLEAR,
 	GPIOC_TOGGLE,
+#ifdef CONFIG_CMD_GPIO_READ
+	GPIOC_READ,
+#endif
 };
 
 #if defined(CONFIG_DM_GPIO) && !defined(gpio_status)
@@ -125,6 +131,9 @@ static int do_gpio(struct cmd_tbl *cmdtp, int flag, int argc,
 	enum gpio_cmd sub_cmd;
 	int value;
 	const char *str_cmd, *str_gpio = NULL;
+#ifdef CONFIG_CMD_GPIO_READ
+	const char *str_var = NULL;
+#endif
 	int ret;
 #ifdef CONFIG_DM_GPIO
 	bool all = false;
@@ -137,11 +146,20 @@ static int do_gpio(struct cmd_tbl *cmdtp, int flag, int argc,
 	argc -= 2;
 	argv += 2;
 #ifdef CONFIG_DM_GPIO
-	if (argc > 0 && !strcmp(*argv, "-a")) {
+	if (argc > 0 && !strncmp(str_cmd, "status", 2) && !strcmp(*argv, "-a")) {
 		all = true;
 		argc--;
 		argv++;
 	}
+#endif
+#ifdef CONFIG_CMD_GPIO_READ
+	if (argc > 0 && !strncmp(str_cmd, "read", 2)) {
+		if (argc < 2)
+			goto show_usage;
+		str_var = *argv;
+		argc--;
+		argv++;
+	}
 #endif
 	if (argc > 0)
 		str_gpio = *argv;
@@ -174,6 +192,11 @@ static int do_gpio(struct cmd_tbl *cmdtp, int flag, int argc,
 	case 't':
 		sub_cmd = GPIOC_TOGGLE;
 		break;
+#ifdef CONFIG_CMD_GPIO_READ
+	case 'r':
+		sub_cmd = GPIOC_READ;
+		break;
+#endif
 	default:
 		goto show_usage;
 	}
@@ -205,7 +228,11 @@ static int do_gpio(struct cmd_tbl *cmdtp, int flag, int argc,
 	}
 
 	/* finally, let's do it: set direction and exec command */
-	if (sub_cmd == GPIOC_INPUT) {
+	if (sub_cmd == GPIOC_INPUT
+#ifdef CONFIG_CMD_GPIO_READ
+			|| sub_cmd == GPIOC_READ
+#endif
+			) {
 		gpio_direction_input(gpio);
 		value = gpio_get_value(gpio);
 	} else {
@@ -233,9 +260,17 @@ static int do_gpio(struct cmd_tbl *cmdtp, int flag, int argc,
 		goto err;
 	} else {
 		printf("%d\n", value);
+#ifdef CONFIG_CMD_GPIO_READ
+		if (sub_cmd == GPIOC_READ)
+			env_set_ulong(str_var, (ulong)value);
+#endif
 	}
 
-	if (sub_cmd != GPIOC_INPUT && !IS_ERR_VALUE(value)) {
+	if (sub_cmd != GPIOC_INPUT && !IS_ERR_VALUE(value)
+#ifdef CONFIG_CMD_GPIO_READ
+			&& sub_cmd != GPIOC_READ
+#endif
+			) {
 		int nval = gpio_get_value(gpio);
 
 		if (IS_ERR_VALUE(nval)) {
@@ -267,4 +302,8 @@ U_BOOT_CMD(gpio, 4, 0, do_gpio,
 	   "query and control gpio pins",
 	   "<input|set|clear|toggle> <pin>\n"
 	   "    - input/set/clear/toggle the specified pin\n"
+#ifdef CONFIG_CMD_GPIO_READ
+	   "gpio read <name> <pin>\n"
+	   "    - set environment variable 'name' to the specified pin\n"
+#endif
 	   "gpio status [-a] [<bank> | <pin>]  - show [all/claimed] GPIOs");

configs/sandbox_defconfig

@@ -60,6 +60,7 @@ CONFIG_CMD_UNZIP=y
 CONFIG_CMD_BIND=y
 CONFIG_CMD_DEMO=y
 CONFIG_CMD_GPIO=y
+CONFIG_CMD_GPIO_READ=y
 CONFIG_CMD_PWM=y
 CONFIG_CMD_GPT=y
 CONFIG_CMD_GPT_RENAME=y

test/py/tests/test_gpio.py

@@ -46,6 +46,20 @@ def test_gpio_exit_statuses(u_boot_console):
     response = u_boot_console.run_command('gpio input 200; echo rc:$?')
     assert(expected_response in response)
 
+@pytest.mark.boardspec('sandbox')
+@pytest.mark.buildconfigspec('cmd_gpio')
+def test_gpio_read(u_boot_console):
+    """Test that gpio read correctly sets the variable to the value of a gpio pin."""
+
+    response = u_boot_console.run_command('gpio read var 0; echo val:$var,rc:$?')
+    expected_response = 'val:0,rc:0'
+    assert(expected_response in response)
+    response = u_boot_console.run_command('gpio toggle 0; gpio read var 0; echo val:$var,rc:$?')
+    expected_response = 'val:1,rc:0'
+    assert(expected_response in response)
+    response = u_boot_console.run_command('setenv var; gpio read var nonexistent-gpio; echo val:$var,rc:$?')
+    expected_response = 'val:,rc:1'
+    assert(expected_response in response)
 
 """
 Generic Tests for 'gpio' command on sandbox and real hardware.