iio: __iio_update_buffers: Verify configuration before starting to apply it

Currently __iio_update_buffers() verifies whether the new configuration
will work in the middle of the update sequence. This means if the new
configuration is invalid we need to rollback the changes already made. This
patch moves the validation of the new configuration at the beginning of
__iio_update_buffers() and will not start to make any changes if the new
configuration is invalid.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/iio/industrialio-buffer.c

@@ -602,20 +602,104 @@ static void iio_free_scan_mask(struct iio_dev *indio_dev,
 		kfree(mask);
 }
 
+struct iio_device_config {
+	unsigned int mode;
+	const unsigned long *scan_mask;
+	unsigned int scan_bytes;
+	bool scan_timestamp;
+};
+
+static int iio_verify_update(struct iio_dev *indio_dev,
+	struct iio_buffer *insert_buffer, struct iio_buffer *remove_buffer,
+	struct iio_device_config *config)
+{
+	unsigned long *compound_mask;
+	const unsigned long *scan_mask;
+	struct iio_buffer *buffer;
+	bool scan_timestamp;
+
+	memset(config, 0, sizeof(*config));
+
+	/*
+	 * If there is just one buffer and we are removing it there is nothing
+	 * to verify.
+	 */
+	if (remove_buffer && !insert_buffer &&
+		list_is_singular(&indio_dev->buffer_list))
+			return 0;
+
+	/* Definitely possible for devices to support both of these. */
+	if ((indio_dev->modes & INDIO_BUFFER_TRIGGERED) && indio_dev->trig) {
+		config->mode = INDIO_BUFFER_TRIGGERED;
+	} else if (indio_dev->modes & INDIO_BUFFER_HARDWARE) {
+		config->mode = INDIO_BUFFER_HARDWARE;
+	} else if (indio_dev->modes & INDIO_BUFFER_SOFTWARE) {
+		config->mode = INDIO_BUFFER_SOFTWARE;
+	} else {
+		/* Can only occur on first buffer */
+		if (indio_dev->modes & INDIO_BUFFER_TRIGGERED)
+			dev_dbg(&indio_dev->dev, "Buffer not started: no trigger\n");
+		return -EINVAL;
+	}
+
+	/* What scan mask do we actually have? */
+	compound_mask = kcalloc(BITS_TO_LONGS(indio_dev->masklength),
+				sizeof(long), GFP_KERNEL);
+	if (compound_mask == NULL)
+		return -ENOMEM;
+
+	scan_timestamp = false;
+
+	list_for_each_entry(buffer, &indio_dev->buffer_list, buffer_list) {
+		if (buffer == remove_buffer)
+			continue;
+		bitmap_or(compound_mask, compound_mask, buffer->scan_mask,
+			  indio_dev->masklength);
+		scan_timestamp |= buffer->scan_timestamp;
+	}
+
+	if (insert_buffer) {
+		bitmap_or(compound_mask, compound_mask,
+			  insert_buffer->scan_mask, indio_dev->masklength);
+		scan_timestamp |= insert_buffer->scan_timestamp;
+	}
+
+	if (indio_dev->available_scan_masks) {
+		scan_mask = iio_scan_mask_match(indio_dev->available_scan_masks,
+				    indio_dev->masklength,
+				    compound_mask);
+		kfree(compound_mask);
+		if (scan_mask == NULL)
+			return -EINVAL;
+	} else {
+	    scan_mask = compound_mask;
+	}
+
+	config->scan_bytes = iio_compute_scan_bytes(indio_dev,
+				    scan_mask, scan_timestamp);
+	config->scan_mask = scan_mask;
+	config->scan_timestamp = scan_timestamp;
+
+	return 0;
+}
+
 static int __iio_update_buffers(struct iio_dev *indio_dev,
 		       struct iio_buffer *insert_buffer,
 		       struct iio_buffer *remove_buffer)
 {
 	int ret;
-	int success = 0;
-	struct iio_buffer *buffer;
-	unsigned long *compound_mask;
 	const unsigned long *old_mask;
+	struct iio_device_config new_config;
+
+	ret = iio_verify_update(indio_dev, insert_buffer, remove_buffer,
+		&new_config);
+	if (ret)
+		return ret;
 
 	if (insert_buffer) {
 		ret = iio_buffer_request_update(indio_dev, insert_buffer);
 		if (ret)
-			return ret;
+			goto err_free_config;
 	}
 
 	/* Wind down existing buffers - iff there are any */
@@ -623,13 +707,13 @@ static int __iio_update_buffers(struct iio_dev *indio_dev,
 		if (indio_dev->setup_ops->predisable) {
 			ret = indio_dev->setup_ops->predisable(indio_dev);
 			if (ret)
-				return ret;
+				goto err_free_config;
 		}
 		indio_dev->currentmode = INDIO_DIRECT_MODE;
 		if (indio_dev->setup_ops->postdisable) {
 			ret = indio_dev->setup_ops->postdisable(indio_dev);
 			if (ret)
-				return ret;
+				goto err_free_config;
 		}
 	}
 	/* Keep a copy of current setup to allow roll back */
@@ -649,44 +733,9 @@ static int __iio_update_buffers(struct iio_dev *indio_dev,
 		return 0;
 	}
 
-	/* What scan mask do we actually have? */
-	compound_mask = kcalloc(BITS_TO_LONGS(indio_dev->masklength),
-				sizeof(long), GFP_KERNEL);
-	if (compound_mask == NULL) {
-		iio_free_scan_mask(indio_dev, old_mask);
-		return -ENOMEM;
-	}
-	indio_dev->scan_timestamp = 0;
-
-	list_for_each_entry(buffer, &indio_dev->buffer_list, buffer_list) {
-		bitmap_or(compound_mask, compound_mask, buffer->scan_mask,
-			  indio_dev->masklength);
-		indio_dev->scan_timestamp |= buffer->scan_timestamp;
-	}
-	if (indio_dev->available_scan_masks) {
-		indio_dev->active_scan_mask =
-			iio_scan_mask_match(indio_dev->available_scan_masks,
-					    indio_dev->masklength,
-					    compound_mask);
-		kfree(compound_mask);
-		if (indio_dev->active_scan_mask == NULL) {
-			/*
-			 * Roll back.
-			 * Note can only occur when adding a buffer.
-			 */
-			iio_buffer_deactivate(insert_buffer);
-			if (old_mask) {
-				indio_dev->active_scan_mask = old_mask;
-				success = -EINVAL;
-			}
-			else {
-				ret = -EINVAL;
-				return ret;
-			}
-		}
-	} else {
-		indio_dev->active_scan_mask = compound_mask;
-	}
+	indio_dev->active_scan_mask = new_config.scan_mask;
+	indio_dev->scan_timestamp = new_config.scan_timestamp;
+	indio_dev->scan_bytes = new_config.scan_bytes;
 
 	iio_update_demux(indio_dev);
 
@@ -699,10 +748,7 @@ static int __iio_update_buffers(struct iio_dev *indio_dev,
 			goto error_remove_inserted;
 		}
 	}
-	indio_dev->scan_bytes =
-		iio_compute_scan_bytes(indio_dev,
-				       indio_dev->active_scan_mask,
-				       indio_dev->scan_timestamp);
+
 	if (indio_dev->info->update_scan_mode) {
 		ret = indio_dev->info
 			->update_scan_mode(indio_dev,
@@ -714,20 +760,8 @@ static int __iio_update_buffers(struct iio_dev *indio_dev,
 			goto error_run_postdisable;
 		}
 	}
-	/* Definitely possible for devices to support both of these. */
-	if ((indio_dev->modes & INDIO_BUFFER_TRIGGERED) && indio_dev->trig) {
-		indio_dev->currentmode = INDIO_BUFFER_TRIGGERED;
-	} else if (indio_dev->modes & INDIO_BUFFER_HARDWARE) {
-		indio_dev->currentmode = INDIO_BUFFER_HARDWARE;
-	} else if (indio_dev->modes & INDIO_BUFFER_SOFTWARE) {
-		indio_dev->currentmode = INDIO_BUFFER_SOFTWARE;
-	} else { /* Should never be reached */
-		/* Can only occur on first buffer */
-		if (indio_dev->modes & INDIO_BUFFER_TRIGGERED)
-			dev_dbg(&indio_dev->dev, "Buffer not started: no trigger\n");
-		ret = -EINVAL;
-		goto error_run_postdisable;
-	}
+
+	indio_dev->currentmode = new_config.mode;
 
 	if (indio_dev->setup_ops->postenable) {
 		ret = indio_dev->setup_ops->postenable(indio_dev);
@@ -743,7 +777,7 @@ static int __iio_update_buffers(struct iio_dev *indio_dev,
 
 	iio_free_scan_mask(indio_dev, old_mask);
 
-	return success;
+	return 0;
 
 error_disable_all_buffers:
 	indio_dev->currentmode = INDIO_DIRECT_MODE;
@@ -756,6 +790,10 @@ error_remove_inserted:
 	iio_free_scan_mask(indio_dev, indio_dev->active_scan_mask);
 	indio_dev->active_scan_mask = old_mask;
 	return ret;
+
+err_free_config:
+	iio_free_scan_mask(indio_dev, new_config.scan_mask);
+	return ret;
 }
 
 int iio_update_buffers(struct iio_dev *indio_dev,