[PATCH v4 1/2] platform/x86: dell-uart-backlight: extract dell_uart_bl_receive_data() helper

[chitranshmandhaniya@gmail.com]

From: Chitransh Mandhaniya <Chitransh_Mandhaniya@dell.com>

Factor the response-byte accumulation and checksum validation out of
dell_uart_bl_receive() into a standalone dell_uart_bl_receive_data()
helper.

The helper returns the number of bytes consumed from the input buffer.
The caller inspects dell_bl->status for the outcome:

  -EBUSY  frame still incomplete
   0      frame received and checksum valid
  -EIO    checksum mismatch

This is a preparatory refactor for adding stray-byte recovery in the
next patch.

No functional change.

Signed-off-by: Chitransh Mandhaniya <Chitransh_Mandhaniya@dell.com>
---
 .../platform/x86/dell/dell-uart-backlight.c   | 42 ++++++++++++-------
 1 file changed, 27 insertions(+), 15 deletions(-)

diff --git a/drivers/platform/x86/dell/dell-uart-backlight.c b/drivers/platform/x86/dell/dell-uart-backlight.c
index f323a667dc2d..5f01ad108338 100644
--- a/drivers/platform/x86/dell/dell-uart-backlight.c
+++ b/drivers/platform/x86/dell/dell-uart-backlight.c
@@ -205,20 +205,13 @@ static const struct backlight_ops dell_uart_backlight_ops = {
 	.get_brightness = dell_uart_get_brightness_op,
 };
 
-static size_t dell_uart_bl_receive(struct serdev_device *serdev, const u8 *data, size_t len)
+/* Process received UART data; returns number of bytes consumed. */
+static size_t dell_uart_bl_receive_data(struct dell_uart_backlight *dell_bl,
+					const u8 *data, size_t len)
 {
-	struct dell_uart_backlight *dell_bl = serdev_device_get_drvdata(serdev);
 	size_t i;
 	u8 csum;
 
-	dev_dbg(dell_bl->dev, "Recv: %*ph\n", (int)len, data);
-
-	/* Throw away unexpected bytes / remainder of response after an error */
-	if (dell_bl->status != -EBUSY) {
-		dev_warn(dell_bl->dev, "Bytes received out of band, dropping them.\n");
-		return len;
-	}
-
 	i = 0;
 	while (i < len && dell_bl->resp_idx != dell_bl->resp_len) {
 		dell_bl->resp[dell_bl->resp_idx] = data[i++];
@@ -231,7 +224,7 @@ static size_t dell_uart_bl_receive(struct serdev_device *serdev, const u8 *data,
 				dev_err(dell_bl->dev, "Response length %d out if range %d - %d\n",
 					dell_bl->resp_len, MIN_RESP_LEN, dell_bl->resp_max_len);
 				dell_bl->status = -EIO;
-				goto wakeup;
+				return i;
 			}
 			break;
 		case RESP_CMD: /* CMD byte */
@@ -239,7 +232,7 @@ static size_t dell_uart_bl_receive(struct serdev_device *serdev, const u8 *data,
 				dev_err(dell_bl->dev, "Response cmd 0x%02x != pending 0x%02x\n",
 					dell_bl->resp[RESP_CMD], dell_bl->pending_cmd);
 				dell_bl->status = -EIO;
-				goto wakeup;
+				return i;
 			}
 			break;
 		}
@@ -247,7 +240,7 @@ static size_t dell_uart_bl_receive(struct serdev_device *serdev, const u8 *data,
 	}
 
 	if (dell_bl->resp_idx != dell_bl->resp_len)
-		return len; /* Response not complete yet */
+		return i; /* Response not complete, status stays -EBUSY */
 
 	csum = dell_uart_checksum(dell_bl->resp, dell_bl->resp_len - 1);
 	if (dell_bl->resp[dell_bl->resp_len - 1] == csum) {
@@ -257,11 +250,30 @@ static size_t dell_uart_bl_receive(struct serdev_device *serdev, const u8 *data,
 			dell_bl->resp[dell_bl->resp_len - 1], csum);
 		dell_bl->status = -EIO;
 	}
-wakeup:
-	wake_up(&dell_bl->wait_queue);
 	return i;
 }
 
+static size_t dell_uart_bl_receive(struct serdev_device *serdev, const u8 *data, size_t len)
+{
+	struct dell_uart_backlight *dell_bl = serdev_device_get_drvdata(serdev);
+	size_t ret;
+
+	dev_dbg(dell_bl->dev, "Recv: %*ph\n", (int)len, data);
+
+	/* Throw away unexpected bytes / remainder of response after an error */
+	if (dell_bl->status != -EBUSY) {
+		dev_warn(dell_bl->dev, "Bytes received out of band, dropping them.\n");
+		return len;
+	}
+
+	ret = dell_uart_bl_receive_data(dell_bl, data, len);
+	if (dell_bl->status == -EBUSY)
+		return ret; /* Response not complete yet, waiting for more data */
+
+	wake_up(&dell_bl->wait_queue);
+	return ret;
+}
+
 static const struct serdev_device_ops dell_uart_bl_serdev_ops = {
 	.receive_buf = dell_uart_bl_receive,
 	.write_wakeup = serdev_device_write_wakeup,
-- 
2.43.0