HID: uclogic: Refactor UGEE v2 string descriptor parsing

The UGEE v2 tablets expose a string descriptor with their capabilities.

Move the code used to parse the descriptors and generate a parameter
list from it to its own function and add KUnit tests to validate the
parser.

Tested-by: Jouke Witteveen <j.witteveen@gmail.com>
Signed-off-by: José Expósito <jose.exposito89@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

1 files changed, 66 insertions, 20 deletions

diff --git a/drivers/hid/hid-uclogic-params.c b/drivers/hid/hid-uclogic-params.c
index c11fa239e6a2..07c5a21112ce 100644
--- a/drivers/hid/hid-uclogic-params.c
+++ b/drivers/hid/hid-uclogic-params.c
@@ -1057,6 +1057,62 @@ cleanup:
 }
 
 /**
+ * uclogic_params_parse_ugee_v2_desc - parse the string descriptor containing
+ * pen and frame parameters returned by UGEE v2 devices.
+ *
+ * @str_desc:		String descriptor, cannot be NULL.
+ * @str_desc_size:	Size of the string descriptor.
+ * @desc_params:	Output description params list.
+ * @desc_params_size:	Size of the output description params list.
+ *
+ * Returns:
+ *	Zero, if successful. A negative errno code on error.
+ */
+static int uclogic_params_parse_ugee_v2_desc(const __u8 *str_desc,
+					     size_t str_desc_size,
+					     s32 *desc_params,
+					     size_t desc_params_size)
+{
+	s32 pen_x_lm, pen_y_lm;
+	s32 pen_x_pm, pen_y_pm;
+	s32 pen_pressure_lm;
+	s32 frame_num_buttons;
+	s32 resolution;
+
+	/* Minimum descriptor length required, maximum seen so far is 14 */
+	const int min_str_desc_size = 12;
+
+	if (!str_desc || str_desc_size < min_str_desc_size)
+		return -EINVAL;
+
+	if (desc_params_size != UCLOGIC_RDESC_PH_ID_NUM)
+		return -EINVAL;
+
+	pen_x_lm = get_unaligned_le16(str_desc + 2);
+	pen_y_lm = get_unaligned_le16(str_desc + 4);
+	frame_num_buttons = str_desc[6];
+	pen_pressure_lm = get_unaligned_le16(str_desc + 8);
+
+	resolution = get_unaligned_le16(str_desc + 10);
+	if (resolution == 0) {
+		pen_x_pm = 0;
+		pen_y_pm = 0;
+	} else {
+		pen_x_pm = pen_x_lm * 1000 / resolution;
+		pen_y_pm = pen_y_lm * 1000 / resolution;
+	}
+
+	desc_params[UCLOGIC_RDESC_PEN_PH_ID_X_LM] = pen_x_lm;
+	desc_params[UCLOGIC_RDESC_PEN_PH_ID_X_PM] = pen_x_pm;
+	desc_params[UCLOGIC_RDESC_PEN_PH_ID_Y_LM] = pen_y_lm;
+	desc_params[UCLOGIC_RDESC_PEN_PH_ID_Y_PM] = pen_y_pm;
+	desc_params[UCLOGIC_RDESC_PEN_PH_ID_PRESSURE_LM] = pen_pressure_lm;
+	desc_params[UCLOGIC_RDESC_FRAME_PH_ID_UM] = frame_num_buttons;
+
+	return 0;
+}
+
+/**
  * uclogic_params_ugee_v2_init() - initialize a UGEE graphics tablets by
  * discovering their parameters.
  *
@@ -1086,7 +1142,6 @@ static int uclogic_params_ugee_v2_init(struct uclogic_params *params,
 	__u8 *rdesc_pen = NULL;
 	__u8 *rdesc_frame = NULL;
 	s32 desc_params[UCLOGIC_RDESC_PH_ID_NUM];
-	s32 resolution;
 	__u8 magic_arr[] = {
 		0x02, 0xb0, 0x04, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00
 	};
@@ -1128,25 +1183,12 @@ static int uclogic_params_ugee_v2_init(struct uclogic_params *params,
 		goto output;
 	}
 
-	desc_params[UCLOGIC_RDESC_PEN_PH_ID_X_LM] =
-		get_unaligned_le16(str_desc + 2);
-	desc_params[UCLOGIC_RDESC_PEN_PH_ID_Y_LM] =
-		get_unaligned_le16(str_desc + 4);
-	desc_params[UCLOGIC_RDESC_FRAME_PH_ID_UM] = str_desc[6];
-	desc_params[UCLOGIC_RDESC_PEN_PH_ID_PRESSURE_LM] =
-		get_unaligned_le16(str_desc + 8);
-	resolution = get_unaligned_le16(str_desc + 10);
-	if (resolution == 0) {
-		desc_params[UCLOGIC_RDESC_PEN_PH_ID_X_PM] = 0;
-		desc_params[UCLOGIC_RDESC_PEN_PH_ID_Y_PM] = 0;
-	} else {
-		desc_params[UCLOGIC_RDESC_PEN_PH_ID_X_PM] =
-			desc_params[UCLOGIC_RDESC_PEN_PH_ID_X_LM] * 1000 /
-			resolution;
-		desc_params[UCLOGIC_RDESC_PEN_PH_ID_Y_PM] =
-			desc_params[UCLOGIC_RDESC_PEN_PH_ID_Y_LM] * 1000 /
-			resolution;
-	}
+	rc = uclogic_params_parse_ugee_v2_desc(str_desc, str_desc_len,
+					       desc_params,
+					       ARRAY_SIZE(desc_params));
+	if (rc)
+		goto cleanup;
+
 	kfree(str_desc);
 	str_desc = NULL;
 
@@ -1517,3 +1559,7 @@ cleanup:
 	uclogic_params_cleanup(&p);
 	return rc;
 }
+
+#ifdef CONFIG_HID_KUNIT_TEST
+#include "hid-uclogic-params-test.c"
+#endif