Add additional error logging in NPU driver

To make it easier to distinguish where an error occurred in the NPU
driver, additional logging has been added to the error cases.

Change-Id: I9d744e7adf3ba3098d456d1f3c2859aa0ce66de4
Signed-off-by: Mikael Olsson <mikael.olsson@arm.com>
diff --git a/kernel/common/ethosu_buffer.c b/kernel/common/ethosu_buffer.c
index cf41b8d..519e270 100644
--- a/kernel/common/ethosu_buffer.c
+++ b/kernel/common/ethosu_buffer.c
@@ -139,12 +139,18 @@
 	struct ethosu_buffer *buf;
 	int ret = -ENOMEM;
 
-	if (!size)
+	if (!size) {
+		dev_err(dev, "Buffer create. Invalid zero size");
+
 		return -EINVAL;
+	}
 
 	buf = devm_kzalloc(dev, sizeof(*buf), GFP_KERNEL);
-	if (!buf)
+	if (!buf) {
+		dev_err(dev, "Buffer create. Failed to allocate struct");
+
 		return -ENOMEM;
+	}
 
 	buf->dev = dev;
 	kref_init(&buf->kref);
@@ -152,13 +158,20 @@
 	buf->dma_mem = ethosu_dma_mem_alloc(dev, size);
 	if (IS_ERR(buf->dma_mem)) {
 		ret = PTR_ERR(buf->dma_mem);
+		dev_err(dev,
+			"Buffer create. Failed to allocate DMA memory. ret=%d",
+			ret);
 		goto free_buf;
 	}
 
 	ret = anon_inode_getfd("ethosu-buffer", &ethosu_buffer_fops, buf,
 			       O_RDWR | O_CLOEXEC);
-	if (ret < 0)
+	if (ret < 0) {
+		dev_err(dev,
+			"Buffer create. Failed to get file descriptor. ret=%d",
+			ret);
 		goto free_dma;
+	}
 
 	buf->file = fget(ret);
 	buf->file->f_mode |= FMODE_LSEEK;