path: root/drivers/hid/hid-uclogic-params.c

// SPDX-License-Identifier: GPL-2.0+
/*
 *  HID driver for UC-Logic devices not fully compliant with HID standard
 *  - tablet initialization and parameter retrieval
 *
 *  Copyright (c) 2018 Nikolai Kondrashov
 */

/*
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by the Free
 * Software Foundation; either version 2 of the License, or (at your option)
 * any later version.
 */

#include "hid-uclogic-params.h"
#include "hid-uclogic-rdesc.h"
#include "usbhid/usbhid.h"
#include "hid-ids.h"
#include <linux/ctype.h>
#include <asm/unaligned.h>

/**
 * Convert a pen in-range reporting type to a string.
 *
 * @inrange:	The in-range reporting type to convert.
 *
 * Returns:
 *	The string representing the type, or NULL if the type is unknown.
 */
const char *uclogic_params_pen_inrange_to_str(
			enum uclogic_params_pen_inrange inrange)
{
	switch (inrange) {
	case UCLOGIC_PARAMS_PEN_INRANGE_NORMAL:
		return "normal";
	case UCLOGIC_PARAMS_PEN_INRANGE_INVERTED:
		return "inverted";
	case UCLOGIC_PARAMS_PEN_INRANGE_NONE:
		return "none";
	default:
		return NULL;
	}
}

/**
 * uclogic_params_get_str_desc - retrieve a string descriptor from a HID
 * device interface, putting it into a kmalloc-allocated buffer as is, without
 * character encoding conversion.
 *
 * @pbuf:	Location for the kmalloc-allocated buffer pointer containing
 *		the retrieved descriptor. Not modified in case of error.
 *		Can be NULL to have retrieved descriptor discarded.
 * @hdev:	The HID device of the tablet interface to retrieve the string
 *		descriptor from. Cannot be NULL.
 * @idx:	Index of the string descriptor to request from the device.
 * @len:	Length of the buffer to allocate and the data to retrieve.
 *
 * Returns:
 *	number of bytes retrieved (<= len),
 *	-EPIPE, if the descriptor was not found, or
 *	another negative errno code in case of other error.
 */
static int uclogic_params_get_str_desc(__u8 **pbuf, struct hid_device *hdev,
					__u8 idx, size_t len)
{
	int rc;
	struct usb_device *udev;
	__u8 *buf = NULL;

	/* Check arguments */
	if (hdev == NULL) {
		rc = -EINVAL;
		goto cleanup;
	}

	udev = hid_to_usb_dev(hdev);

	buf = kmalloc(len, GFP_KERNEL);
	if (buf == NULL) {
		rc = -ENOMEM;
		goto cleanup;
	}

	rc = usb_control_msg(udev, usb_rcvctrlpipe(udev, 0),
				USB_REQ_GET_DESCRIPTOR, USB_DIR_IN,
				(USB_DT_STRING << 8) + idx,
				0x0409, buf, len,
				USB_CTRL_GET_TIMEOUT);
	if (rc == -EPIPE) {
		hid_dbg(hdev, "string descriptor #%hhu not found\n", idx);
		goto cleanup;
	} else if (rc < 0) {
		hid_err(hdev,
			"failed retrieving string descriptor #%hhu: %d\n",
			idx, rc);
		goto cleanup;
	}

	if (pbuf != NULL) {
		*pbuf = buf;
		buf = NULL;
	}

cleanup:
	kfree(buf);
	return rc;
}

/**
 * uclogic_params_pen_cleanup - free resources used by struct
 * uclogic_params_pen (tablet interface's pen input parameters).
 * Can be called repeatedly.
 *
 * @pen:	Pen input parameters to cleanup. Cannot be NULL.
 */
static void uclogic_params_pen_cleanup(struct uclogic_params_pen *pen)
{
	kfree(pen->desc_ptr);
	memset(pen, 0, sizeof(*pen));
}

/**
 * uclogic_params_pen_init_v1() - initialize tablet interface pen
 * input and retrieve its parameters from the device, using v1 protocol.
 *
 * @pen:	Pointer to the pen parameters to initialize (to be
 *		cleaned up with uclogic_params_pen_cleanup()). Not modified in
 *		case of error, or if parameters are not found. Cannot be NULL.
 * @pfound:	Location for a flag which is set to true if the parameters
 *		were found, and to false if not (e.g. device was
 *		incompatible). Not modified in case of error. Cannot be NULL.
 * @hdev:	The HID device of the tablet interface to initialize and get
 *		parameters from. Cannot be NULL.
 *
 * Returns:
 *	Zero, if successful. A negative errno code on error.
 */
static int uclogic_params_pen_init_v1(struct uclogic_params_pen *pen,
				      bool *pfound,
				      struct hid_device *hdev)
{
	int rc;
	bool found = false;
	/* Buffer for (part of) the string descriptor */
	__u8 *buf = NULL;
	/* Minimum descriptor length required, maximum seen so far is 18 */
	const int len = 12;
	s32 resolution;
	/* Pen report descriptor template parameters */
	s32 desc_params[UCLOGIC_RDESC_PEN_PH_ID_NUM];
	__u8 *desc_ptr = NULL;

	/* Check arguments */
	if (pen == NULL || pfound == NULL || hdev == NULL) {
		rc = -EINVAL;
		goto cleanup;
	}

	/*
	 * Read string descriptor containing pen input parameters.
	 * The specific string descriptor and data were discovered by sniffing
	 * the Windows driver traffic.
	 * NOTE: This enables fully-functional tablet mode.
	 */
	rc = uclogic_params_get_str_desc(&buf, hdev, 100, len);
	if (rc == -EPIPE) {
		hid_dbg(hdev,
			"string descriptor with pen parameters not found, assuming not compatible\n");
		goto finish;
	} else if (rc < 0) {
		hid_err(hdev, "failed retrieving pen parameters: %d\n", rc);
		goto cleanup;
	} else if (rc != len) {
		hid_dbg(hdev,
			"string descriptor with pen parameters has invalid length (got %d, expected %d), assuming not compatible\n",
			rc, len);
		goto finish;
	}

	/*
	 * Fill report descriptor parameters from the string descriptor
	 */
	desc_params[UCLOGIC_RDESC_PEN_PH_ID_X_LM] =
		get_unaligned_le16(buf + 2);
	desc_params[UCLOGIC_RDESC_PEN_PH_ID_Y_LM] =
		get_unaligned_le16(buf + 4);
	desc_params[UCLOGIC_RDESC_PEN_PH_ID_PRESSURE_LM] =
		get_unaligned_le16(buf + 8);
	resolution =