[libgpiod,v2,3/8] core: provide gpiod_line_config_set_output_values()

diff --git a/include/gpiod.h b/include/gpiod.h
index fea2076..a895dae 100644
--- a/include/gpiod.h
+++ b/include/gpiod.h
@@ -785,6 +785,31 @@  struct gpiod_line_settings *
 gpiod_line_config_get_line_settings(struct gpiod_line_config *config,
 				    unsigned int offset);
 
+/**
+ * @brief Set output values for a number of lines.
+ * @param config Line config object.
+ * @param values Buffer containing the output values.
+ * @param num_values Number of values in the buffer.
+ * @return 0 on success, -1 on error.
+ *
+ * This is a helper that allows users to set multiple (potentially different)
+ * output values at once while using the same line settings object. Instead of
+ * modifying the output value in the settings object and calling
+ * ::gpiod_line_config_add_line_settings multiple times, we can specify the
+ * settings, add them for a set of offsets and then call this function to
+ * set the output values.
+ *
+ * Values set by this function override whatever values were specified in the
+ * regular line settings.
+ *
+ * Each value must be associated with the line identified by the corresponding
+ * entry in the offset array filled by
+ * ::gpiod_line_request_get_requested_offsets.
+ */
+int gpiod_line_config_set_output_values(struct gpiod_line_config *config,
+					const enum gpiod_line_value *values,
+					size_t num_values);
+
 /**
  * @brief Get the number of configured line offsets.
  * @param config Line config object.
diff --git a/lib/line-config.c b/lib/line-config.c
index 877e7ef..fef62de 100644
--- a/lib/line-config.c
+++ b/lib/line-config.c
@@ -25,6 +25,8 @@  struct per_line_config {
 struct gpiod_line_config {
 	struct per_line_config line_configs[LINES_MAX];
 	size_t num_configs;
+	enum gpiod_line_value output_values[LINES_MAX];
+	size_t num_output_values;
 	struct settings_node *sref_list;
 };
 
@@ -136,23 +138,60 @@  GPIOD_API struct gpiod_line_settings *
 gpiod_line_config_get_line_settings(struct gpiod_line_config *config,
 				    unsigned int offset)
 {
+	struct gpiod_line_settings *settings;
 	struct per_line_config *per_line;
 	size_t i;
+	int ret;
 
 	assert(config);
 
 	for (i = 0; i < config->num_configs; i++) {
 		per_line = &config->line_configs[i];
 
-		if (per_line->offset == offset)
-			return gpiod_line_settings_copy(
+		if (per_line->offset == offset) {
+			settings = gpiod_line_settings_copy(
 					per_line->node->settings);
+			if (!settings)
+				return NULL;
+
+			/*
+			 * If a global output value was set for this line - use
+			 * it and override the one stored in settings.
+			 */
+			if (config->num_output_values > i) {
+				ret = gpiod_line_settings_set_output_value(
+						settings,
+						config->output_values[i]);
+				if (ret) {
+					gpiod_line_settings_free(settings);
+					return NULL;
+				}
+			}
+
+			return settings;
+		}
 	}
 
 	errno = ENOENT;
 	return NULL;
 }
 
+GPIOD_API int
+gpiod_line_config_set_output_values(struct gpiod_line_config *config,
+				    const enum gpiod_line_value *values,
+				    size_t num_values)
+{
+	if (num_values > LINES_MAX) {
+		errno = EINVAL;
+		return -1;
+	}
+
+	memcpy(config->output_values, values, num_values * sizeof(*values));
+	config->num_output_values = num_values;
+
+	return 0;
+}
+
 GPIOD_API size_t
 gpiod_line_config_get_num_configured_offsets(struct gpiod_line_config *config)
 {
@@ -206,6 +245,13 @@  static bool has_at_least_one_output_direction(struct gpiod_line_config *config)
 	return false;
 }
 
+static void set_output_value(uint64_t *vals, size_t bit,
+			     enum gpiod_line_value value)
+{
+	gpiod_line_mask_assign_bit(vals, bit,
+				   value == GPIOD_LINE_VALUE_ACTIVE ? 1 : 0);
+}
+
 static void set_kernel_output_values(uint64_t *mask, uint64_t *vals,
 				     struct gpiod_line_config *config)
 {
@@ -227,8 +273,14 @@  static void set_kernel_output_values(uint64_t *mask, uint64_t *vals,
 		gpiod_line_mask_set_bit(mask, i);
 		value = gpiod_line_settings_get_output_value(
 			per_line->node->settings);
-		gpiod_line_mask_assign_bit(
-			vals, i, value == GPIOD_LINE_VALUE_ACTIVE ? 1 : 0);
+		set_output_value(vals, i, value);
+	}
+
+	/* "Global" output values override the ones from per-line settings. */
+	for (i = 0; i < config->num_output_values; i++) {
+		gpiod_line_mask_set_bit(mask, i);
+		value = config->output_values[i];
+		set_output_value(vals, i, value);
 	}
 }
 
diff --git a/tests/gpiod-test-helpers.h b/tests/gpiod-test-helpers.h
index fb3fd7d..760949e 100644
--- a/tests/gpiod-test-helpers.h
+++ b/tests/gpiod-test-helpers.h
@@ -136,6 +136,16 @@  G_DEFINE_AUTOPTR_CLEANUP_FUNC(struct_gpiod_edge_event_buffer,
 		_settings; \
 	})
 
+#define gpiod_test_line_config_set_output_values_or_fail(_line_cfg, _values, \
+							 _num_values) \
+	do { \
+		gint _ret = gpiod_line_config_set_output_values(_line_cfg, \
+								_values, \
+								_num_values); \
+		g_assert_cmpint(_ret, ==, 0); \
+		gpiod_test_return_if_failed(); \
+	} while (0)
+
 #define gpiod_test_create_request_config_or_fail() \
 	({ \
 		struct gpiod_request_config *_config = \
diff --git a/tests/tests-line-config.c b/tests/tests-line-config.c
index a1a587d..78c4d6b 100644
--- a/tests/tests-line-config.c
+++ b/tests/tests-line-config.c
@@ -280,3 +280,70 @@  GPIOD_TEST_CASE(get_more_offsets_than_configured)
 	g_assert_cmpuint(retrieved[2], ==, 2);
 	g_assert_cmpuint(retrieved[3], ==, 3);
 }
+
+GPIOD_TEST_CASE(set_global_output_values)
+{
+	static const guint offsets[] = { 0, 1, 2, 3 };
+	static const enum gpiod_line_value values[] = {
+		GPIOD_LINE_VALUE_ACTIVE,
+		GPIOD_LINE_VALUE_INACTIVE,
+		GPIOD_LINE_VALUE_ACTIVE,
+		GPIOD_LINE_VALUE_INACTIVE,
+	};
+
+	g_autoptr(GPIOSimChip) sim = g_gpiosim_chip_new("num-lines", 4, NULL);
+	g_autoptr(struct_gpiod_line_settings) settings = NULL;
+	g_autoptr(struct_gpiod_line_config) config = NULL;
+	g_autoptr(struct_gpiod_line_request) request = NULL;
+	g_autoptr(struct_gpiod_chip) chip = NULL;
+
+	chip = gpiod_test_open_chip_or_fail(g_gpiosim_chip_get_dev_path(sim));
+	settings = gpiod_test_create_line_settings_or_fail();
+	config = gpiod_test_create_line_config_or_fail();
+
+	gpiod_line_settings_set_direction(settings,
+					  GPIOD_LINE_DIRECTION_OUTPUT);
+	gpiod_test_line_config_add_line_settings_or_fail(config, offsets, 4,
+							 settings);
+	gpiod_test_line_config_set_output_values_or_fail(config, values, 4);
+
+	request = gpiod_test_request_lines_or_fail(chip, NULL, config);
+
+	g_assert_cmpint(g_gpiosim_chip_get_value(sim, 0), ==,
+			GPIOD_LINE_VALUE_ACTIVE);
+	g_assert_cmpint(g_gpiosim_chip_get_value(sim, 1), ==,
+			GPIOD_LINE_VALUE_INACTIVE);
+	g_assert_cmpint(g_gpiosim_chip_get_value(sim, 2), ==,
+			GPIOD_LINE_VALUE_ACTIVE);
+	g_assert_cmpint(g_gpiosim_chip_get_value(sim, 3), ==,
+			GPIOD_LINE_VALUE_INACTIVE);
+}
+
+GPIOD_TEST_CASE(read_back_global_output_values)
+{
+	static const guint offsets[] = { 0, 1, 2, 3 };
+	static const enum gpiod_line_value values[] = {
+		GPIOD_LINE_VALUE_ACTIVE,
+		GPIOD_LINE_VALUE_INACTIVE,
+		GPIOD_LINE_VALUE_ACTIVE,
+		GPIOD_LINE_VALUE_INACTIVE,
+	};
+
+	g_autoptr(struct_gpiod_line_settings) settings = NULL;
+	g_autoptr(struct_gpiod_line_settings) retrieved = NULL;
+	g_autoptr(struct_gpiod_line_config) config = NULL;
+
+	settings = gpiod_test_create_line_settings_or_fail();
+	config = gpiod_test_create_line_config_or_fail();
+
+	gpiod_line_settings_set_direction(settings,
+					  GPIOD_LINE_DIRECTION_OUTPUT);
+	gpiod_line_settings_set_output_value(settings, GPIOD_LINE_VALUE_ACTIVE);
+	gpiod_test_line_config_add_line_settings_or_fail(config, offsets, 4,
+							 settings);
+	gpiod_test_line_config_set_output_values_or_fail(config, values, 4);
+
+	retrieved = gpiod_test_line_config_get_line_settings_or_fail(config, 1);
+	g_assert_cmpint(gpiod_line_settings_get_output_value(retrieved), ==,
+			GPIOD_LINE_VALUE_INACTIVE);
+}