[PATCH v4 2/8] HID: uclogic: Refactor UGEE v2 string descriptor parsing

[José Expósito]

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@xxxxxxxxx>
Signed-off-by: José Expósito <jose.exposito89@xxxxxxxxx>
---
 drivers/hid/Makefile                  |   1 +
 drivers/hid/hid-uclogic-params-test.c | 159 ++++++++++++++++++++++++++
 drivers/hid/hid-uclogic-params.c      |  86 ++++++++++----
 3 files changed, 226 insertions(+), 20 deletions(-)
 create mode 100644 drivers/hid/hid-uclogic-params-test.c

diff --git a/drivers/hid/Makefile b/drivers/hid/Makefile
index 82d8fd97d96c..fe69dece2a46 100644
--- a/drivers/hid/Makefile
+++ b/drivers/hid/Makefile
@@ -145,6 +145,7 @@ obj-$(CONFIG_HID_SENSOR_HUB)	+= hid-sensor-hub.o
 obj-$(CONFIG_HID_SENSOR_CUSTOM_SENSOR)	+= hid-sensor-custom.o
 
 hid-uclogic-test-objs		:= hid-uclogic-rdesc.o \
+				   hid-uclogic-params.o \
 				   hid-uclogic-rdesc-test.o
 obj-$(CONFIG_HID_KUNIT_TEST)	+= hid-uclogic-test.o
 
diff --git a/drivers/hid/hid-uclogic-params-test.c b/drivers/hid/hid-uclogic-params-test.c
new file mode 100644
index 000000000000..9f043f2ab387
--- /dev/null
+++ b/drivers/hid/hid-uclogic-params-test.c
@@ -0,0 +1,159 @@
+// SPDX-License-Identifier: GPL-2.0+
+
+/*
+ *  HID driver for UC-Logic devices not fully compliant with HID standard
+ *
+ *  Copyright (c) 2022 José Expósito <jose.exposito89@xxxxxxxxx>
+ */
+
+#include <kunit/test.h>
+#include "./hid-uclogic-rdesc.h"
+
+#define MAX_STR_DESC_SIZE 14
+
+struct uclogic_parse_ugee_v2_desc_case {
+	const char *name;
+	int res;
+	const __u8 str_desc[MAX_STR_DESC_SIZE];
+	size_t str_desc_size;
+	const s32 desc_params[UCLOGIC_RDESC_PH_ID_NUM];
+};
+
+static struct uclogic_parse_ugee_v2_desc_case uclogic_parse_ugee_v2_desc_cases[] = {
+	{
+		.name = "invalid_str_desc",
+		.res = -EINVAL,
+		.str_desc = {},
+		.str_desc_size = 0,
+		.desc_params = {},
+	},
+	{
+		.name = "resolution_with_value_0",
+		.res = 0,
+		.str_desc = {
+			0x0E, 0x03,
+			0x70, 0xB2,
+			0x10, 0x77,
+			0x08,
+			0x00,
+			0xFF, 0x1F,
+			0x00, 0x00,
+		},
+		.str_desc_size = 12,
+		.desc_params = {
+			[UCLOGIC_RDESC_PEN_PH_ID_X_LM] = 0xB270,
+			[UCLOGIC_RDESC_PEN_PH_ID_X_PM] = 0,
+			[UCLOGIC_RDESC_PEN_PH_ID_Y_LM] = 0x7710,
+			[UCLOGIC_RDESC_PEN_PH_ID_Y_PM] = 0,
+			[UCLOGIC_RDESC_PEN_PH_ID_PRESSURE_LM] = 0x1FFF,
+			[UCLOGIC_RDESC_FRAME_PH_ID_UM] = 0x08,
+		},
+	},
+	/* XP-PEN Deco L str_desc: Frame with 8 buttons */
+	{
+		.name = "frame_type_buttons",
+		.res = 0,
+		.str_desc = {
+			0x0E, 0x03,
+			0x70, 0xB2,
+			0x10, 0x77,
+			0x08,
+			0x00,
+			0xFF, 0x1F,
+			0xD8, 0x13,
+		},
+		.str_desc_size = 12,
+		.desc_params = {
+			[UCLOGIC_RDESC_PEN_PH_ID_X_LM] = 0xB270,
+			[UCLOGIC_RDESC_PEN_PH_ID_X_PM] = 0x2320,
+			[UCLOGIC_RDESC_PEN_PH_ID_Y_LM] = 0x7710,
+			[UCLOGIC_RDESC_PEN_PH_ID_Y_PM] = 0x1770,
+			[UCLOGIC_RDESC_PEN_PH_ID_PRESSURE_LM] = 0x1FFF,
+			[UCLOGIC_RDESC_FRAME_PH_ID_UM] = 0x08,
+		},
+	},
+	/* PARBLO A610 PRO str_desc: Frame with 9 buttons and dial */
+	{
+		.name = "frame_type_dial",
+		.res = 0,
+		.str_desc = {
+			0x0E, 0x03,
+			0x96, 0xC7,
+			0xF9, 0x7C,
+			0x09,
+			0x01,
+			0xFF, 0x1F,
+			0xD8, 0x13,
+		},
+		.str_desc_size = 12,
+		.desc_params = {
+			[UCLOGIC_RDESC_PEN_PH_ID_X_LM] = 0xC796,
+			[UCLOGIC_RDESC_PEN_PH_ID_X_PM] = 0x2749,
+			[UCLOGIC_RDESC_PEN_PH_ID_Y_LM] = 0x7CF9,
+			[UCLOGIC_RDESC_PEN_PH_ID_Y_PM] = 0x1899,
+			[UCLOGIC_RDESC_PEN_PH_ID_PRESSURE_LM] = 0x1FFF,
+			[UCLOGIC_RDESC_FRAME_PH_ID_UM] = 0x09,
+		},
+	},
+};
+
+static void uclogic_parse_ugee_v2_desc_case_desc(struct uclogic_parse_ugee_v2_desc_case *t,
+						 char *desc)
+{
+	strscpy(desc, t->name, KUNIT_PARAM_DESC_SIZE);
+}
+
+KUNIT_ARRAY_PARAM(uclogic_parse_ugee_v2_desc, uclogic_parse_ugee_v2_desc_cases,
+		  uclogic_parse_ugee_v2_desc_case_desc);
+
+static void uclogic_parse_ugee_v2_desc_test(struct kunit *test)
+{
+	int res;
+	s32 desc_params[UCLOGIC_RDESC_PH_ID_NUM];
+	const struct uclogic_parse_ugee_v2_desc_case *params = test->param_value;
+
+	res = uclogic_params_parse_ugee_v2_desc(params->str_desc,
+						params->str_desc_size,
+						desc_params,
+						ARRAY_SIZE(desc_params));
+	KUNIT_ASSERT_EQ(test, res, params->res);
+
+	if (res)
+		return;
+
+	KUNIT_EXPECT_EQ(test,
+			params->desc_params[UCLOGIC_RDESC_PEN_PH_ID_X_LM],
+			desc_params[UCLOGIC_RDESC_PEN_PH_ID_X_LM]);
+	KUNIT_EXPECT_EQ(test,
+			params->desc_params[UCLOGIC_RDESC_PEN_PH_ID_X_PM],
+			desc_params[UCLOGIC_RDESC_PEN_PH_ID_X_PM]);
+	KUNIT_EXPECT_EQ(test,
+			params->desc_params[UCLOGIC_RDESC_PEN_PH_ID_Y_LM],
+			desc_params[UCLOGIC_RDESC_PEN_PH_ID_Y_LM]);
+	KUNIT_EXPECT_EQ(test,
+			params->desc_params[UCLOGIC_RDESC_PEN_PH_ID_Y_PM],
+			desc_params[UCLOGIC_RDESC_PEN_PH_ID_Y_PM]);
+	KUNIT_EXPECT_EQ(test,
+			params->desc_params[UCLOGIC_RDESC_PEN_PH_ID_PRESSURE_LM],
+			desc_params[UCLOGIC_RDESC_PEN_PH_ID_PRESSURE_LM]);
+	KUNIT_EXPECT_EQ(test,
+			params->desc_params[UCLOGIC_RDESC_FRAME_PH_ID_UM],
+			desc_params[UCLOGIC_RDESC_FRAME_PH_ID_UM]);
+}
+
+static struct kunit_case hid_uclogic_params_test_cases[] = {
+	KUNIT_CASE_PARAM(uclogic_parse_ugee_v2_desc_test,
+			 uclogic_parse_ugee_v2_desc_gen_params),
+	{}
+};
+
+static struct kunit_suite hid_uclogic_params_test_suite = {
+	.name = "hid_uclogic_params_test",
+	.test_cases = hid_uclogic_params_test_cases,
+};
+
+kunit_test_suite(hid_uclogic_params_test_suite);
+
+MODULE_DESCRIPTION("KUnit tests for the UC-Logic driver");
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("José Expósito <jose.exposito89@xxxxxxxxx>");
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
@@ -1056,6 +1056,62 @@ static int uclogic_probe_interface(struct hid_device *hdev, u8 *magic_arr,
 	return rc;
 }
 
+/**
+ * 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 @@ int uclogic_params_init(struct uclogic_params *params,
 	uclogic_params_cleanup(&p);
 	return rc;
 }
+
+#ifdef CONFIG_HID_KUNIT_TEST
+#include "hid-uclogic-params-test.c"
+#endif
-- 
2.25.1