navio_adc: open fd once and reuse it

Signed-off-by: Nicolae Rosia <nicolae.rosia@gmail.com>

src/drivers/navio_adc/navio_adc.cpp

@@ -93,6 +93,7 @@ private:
 	int read_channel(struct adc_msg_s *adc_msg, int channel);
 
 	pthread_mutex_t _samples_lock;
+	int _fd[ADC_MAX_CHAN];
 	adc_msg_s _samples[ADC_MAX_CHAN];
 };
 
@@ -100,11 +101,21 @@ NavioADC::NavioADC()
 	: DriverFramework::VirtDevObj("navio_adc", ADC0_DEVICE_PATH, ADC_BASE_DEV_PATH, 1e6 / 100)
 {
 	pthread_mutex_init(&_samples_lock, NULL);
+
+	for (int i = 0; i < ADC_MAX_CHAN; i++) {
+		_fd[i] = -1;
+	}
 }
 
 NavioADC::~NavioADC()
 {
 	pthread_mutex_destroy(&_samples_lock);
+
+	for (int i = 0; i < ADC_MAX_CHAN; i++) {
+		if (_fd[i] != -1) {
+			close(_fd[i]);
+		}
+	}
 }
 
 void NavioADC::_measure()
@@ -112,9 +123,20 @@ void NavioADC::_measure()
 	adc_msg_s tmp_samples[ADC_MAX_CHAN];
 
 	for (int i = 0; i < ADC_MAX_CHAN; ++i) {
-		int ret = read_channel(&tmp_samples[i], i);
+		int ret;
+
+		/* Currently we only use these channels */
+		if (i != NAVIO_ADC_BATTERY_VOLTAGE_CHANNEL &&
+		    i != NAVIO_ADC_BATTERY_CURRENT_CHANNEL) {
+			tmp_samples[i].am_channel = i;
+			tmp_samples[i].am_data = 0;
 
-		if (ret != 0) {
+			continue;
+		}
+
+		ret = read_channel(&tmp_samples[i], i);
+
+		if (ret < 0) {
 			PX4_ERR("read_channel(%d): %d", i, ret);
 			tmp_samples[i].am_channel = i;
 			tmp_samples[i].am_data = 0;
@@ -140,7 +162,32 @@ int NavioADC::init()
 		return ret;
 	}
 
+	for (int i = 0; i < ADC_MAX_CHAN; i++) {
+		char channel_path[sizeof(ADC_SYSFS_PATH)];
+		strncpy(channel_path, ADC_SYSFS_PATH, sizeof(ADC_SYSFS_PATH));
+		channel_path[sizeof(ADC_SYSFS_PATH) - 2] += i;
+
+		_fd[i] = ::open(channel_path, O_RDONLY);
+
+		if (_fd[i] == -1) {
+			int err = errno;
+			ret = -1;
+			PX4_ERR("init: open: %s (%d)", strerror(err), err);
+			goto cleanup;
+		}
+	}
+
 	return PX4_OK;
+
+cleanup:
+
+	for (int i = 0; i < ADC_MAX_CHAN; i++) {
+		if (_fd[i] != -1) {
+			close(_fd[i]);
+		}
+	}
+
+	return ret;
 }
 
 int NavioADC::devIOCTL(unsigned long request, unsigned long arg)
@@ -172,36 +219,31 @@ ssize_t NavioADC::devRead(void *buf, size_t count)
 int NavioADC::read_channel(struct adc_msg_s *adc_msg, int channel)
 {
 	char buffer[11]; /* 32bit max INT has maximum 10 chars */
-	char channel_path[sizeof(ADC_SYSFS_PATH)];
-	int fd;
 	int ret;
 
-	if (channel < 0 || channel > 5) {
+	if (channel < 0 || channel >= ADC_MAX_CHAN) {
 		return -EINVAL;
 	}
 
-	strncpy(channel_path, ADC_SYSFS_PATH, sizeof(ADC_SYSFS_PATH));
-	channel_path[sizeof(ADC_SYSFS_PATH) - 2] += channel;
-
-	fd = ::open(channel_path, O_RDONLY);
+	ret = lseek(_fd[channel], 0, SEEK_SET);
 
-	if (fd == -1) {
+	if (ret == -1) {
 		ret = errno;
-		PX4_ERR("read_channel: open: %s (%d)", strerror(ret), ret);
-		return ret;
+		PX4_ERR("read_channel %d: lseek: %s (%d)", channel, strerror(ret), ret);
+		return  ret;
 	}
 
-	ret = ::read(fd, buffer, sizeof(buffer) - 1);
+	ret = ::read(_fd[channel], buffer, sizeof(buffer) - 1);
 
 	if (ret == -1) {
 		ret = errno;
-		PX4_ERR("read_channel: read: %s (%d)", strerror(ret), ret);
-		goto cleanup;
+		PX4_ERR("read_channel %d: read: %s (%d)", channel, strerror(ret), ret);
+		return  ret;
 
 	} else if (ret == 0) {
-		PX4_ERR("read_channel: read empty");
+		PX4_ERR("read_channel %d: read empty", channel);
 		ret = -EINVAL;
-		goto cleanup;
+		return ret;
 	}
 
 	buffer[ret] = 0;
@@ -210,9 +252,6 @@ int NavioADC::read_channel(struct adc_msg_s *adc_msg, int channel)
 	adc_msg->am_data = strtol(buffer, NULL, 10);
 	ret = 0;
 
-cleanup:
-	::close(fd);
-
 	return ret;
 }