HID: mcp2221: Fix GPIO output handling

The mcp2221 driver GPIO output handling has has several issues.

* A wrong value is used for the GPIO direction.

* Wrong offsets are calculated for some GPIO set value/set direction
  operations, when offset is larger than 0.

This has been fixed by introducing proper manifest constants for the
direction encoding, and using 'offsetof' when calculating GPIO
register offsets.

The updated driver has been tested with the Sparx5 pcb134/pcb135
board, which has the mcp2221 device with several (output) GPIO's.

Fixes: 328de1c ("HID: mcp2221: add GPIO functionality support")
Reviewed-by: Rishi Gupta <gupt21@gmail.com>
Signed-off-by: Lars Povlsen <lars.povlsen@microchip.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

drivers/hid/hid-mcp2221.c

@@ -49,6 +49,36 @@ enum {
 	MCP2221_ALT_F_NOT_GPIOD = 0xEF,
 };
 
+/* MCP GPIO direction encoding */
+enum {
+	MCP2221_DIR_OUT = 0x00,
+	MCP2221_DIR_IN = 0x01,
+};
+
+#define MCP_NGPIO	4
+
+/* MCP GPIO set command layout */
+struct mcp_set_gpio {
+	u8 cmd;
+	u8 dummy;
+	struct {
+		u8 change_value;
+		u8 value;
+		u8 change_direction;
+		u8 direction;
+	} gpio[MCP_NGPIO];
+} __packed;
+
+/* MCP GPIO get command layout */
+struct mcp_get_gpio {
+	u8 cmd;
+	u8 dummy;
+	struct {
+		u8 direction;
+		u8 value;
+	} gpio[MCP_NGPIO];
+} __packed;
+
 /*
  * There is no way to distinguish responses. Therefore next command
  * is sent only after response to previous has been received. Mutex
@@ -542,7 +572,7 @@ static int mcp_gpio_get(struct gpio_chip *gc,
 
 	mcp->txbuf[0] = MCP2221_GPIO_GET;
 
-	mcp->gp_idx = (offset + 1) * 2;
+	mcp->gp_idx = offsetof(struct mcp_get_gpio, gpio[offset].value);
 
 	mutex_lock(&mcp->lock);
 	ret = mcp_send_data_req_status(mcp, mcp->txbuf, 1);
@@ -559,7 +589,7 @@ static void mcp_gpio_set(struct gpio_chip *gc,
 	memset(mcp->txbuf, 0, 18);
 	mcp->txbuf[0] = MCP2221_GPIO_SET;
 
-	mcp->gp_idx = ((offset + 1) * 4) - 1;
+	mcp->gp_idx = offsetof(struct mcp_set_gpio, gpio[offset].value);
 
 	mcp->txbuf[mcp->gp_idx - 1] = 1;
 	mcp->txbuf[mcp->gp_idx] = !!value;
@@ -575,7 +605,7 @@ static int mcp_gpio_dir_set(struct mcp2221 *mcp,
 	memset(mcp->txbuf, 0, 18);
 	mcp->txbuf[0] = MCP2221_GPIO_SET;
 
-	mcp->gp_idx = (offset + 1) * 5;
+	mcp->gp_idx = offsetof(struct mcp_set_gpio, gpio[offset].direction);
 
 	mcp->txbuf[mcp->gp_idx - 1] = 1;
 	mcp->txbuf[mcp->gp_idx] = val;
@@ -590,7 +620,7 @@ static int mcp_gpio_direction_input(struct gpio_chip *gc,
 	struct mcp2221 *mcp = gpiochip_get_data(gc);
 
 	mutex_lock(&mcp->lock);
-	ret = mcp_gpio_dir_set(mcp, offset, 0);
+	ret = mcp_gpio_dir_set(mcp, offset, MCP2221_DIR_IN);
 	mutex_unlock(&mcp->lock);
 
 	return ret;
@@ -603,7 +633,7 @@ static int mcp_gpio_direction_output(struct gpio_chip *gc,
 	struct mcp2221 *mcp = gpiochip_get_data(gc);
 
 	mutex_lock(&mcp->lock);
-	ret = mcp_gpio_dir_set(mcp, offset, 1);
+	ret = mcp_gpio_dir_set(mcp, offset, MCP2221_DIR_OUT);
 	mutex_unlock(&mcp->lock);
 
 	/* Can't configure as output, bailout early */
@@ -623,7 +653,7 @@ static int mcp_gpio_get_direction(struct gpio_chip *gc,
 
 	mcp->txbuf[0] = MCP2221_GPIO_GET;
 
-	mcp->gp_idx = (offset + 1) * 2;
+	mcp->gp_idx = offsetof(struct mcp_get_gpio, gpio[offset].direction);
 
 	mutex_lock(&mcp->lock);
 	ret = mcp_send_data_req_status(mcp, mcp->txbuf, 1);
@@ -632,7 +662,7 @@ static int mcp_gpio_get_direction(struct gpio_chip *gc,
 	if (ret)
 		return ret;
 
-	if (mcp->gpio_dir)
+	if (mcp->gpio_dir == MCP2221_DIR_IN)
 		return GPIO_LINE_DIRECTION_IN;
 
 	return GPIO_LINE_DIRECTION_OUT;
@@ -758,7 +788,7 @@ static int mcp2221_raw_event(struct hid_device *hdev,
 				mcp->status = -ENOENT;
 			} else {
 				mcp->status = !!data[mcp->gp_idx];
-				mcp->gpio_dir = !!data[mcp->gp_idx + 1];
+				mcp->gpio_dir = data[mcp->gp_idx + 1];
 			}
 			break;
 		default:
@@ -860,7 +890,7 @@ static int mcp2221_probe(struct hid_device *hdev,
 	mcp->gc->get_direction = mcp_gpio_get_direction;
 	mcp->gc->set = mcp_gpio_set;
 	mcp->gc->get = mcp_gpio_get;
-	mcp->gc->ngpio = 4;
+	mcp->gc->ngpio = MCP_NGPIO;
 	mcp->gc->base = -1;
 	mcp->gc->can_sleep = 1;
 	mcp->gc->parent = &hdev->dev;