First implementation of Media Control
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361
g29_media_usb/g29_media_usb.c
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361
g29_media_usb/g29_media_usb.c
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// SPDX-License-Identifier: GPL-2.0
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/*
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* Logitech G29 -> Media Keys (USB interface driver)
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*
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* Proof-of-concept Linux kernel module for low-level programming course.
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*
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* This driver:
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* - Binds to a Logitech G29 USB interface (VID/PID match)
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* - Receives 12-byte input reports via an interrupt-IN URB
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* - Parses the report into a normalized state (Stage A)
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* - Translates selected signals into media key events (Stage B)
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*
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* Stage A is designed to remain stable across different mapping policies.
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* Stage B is designed to be replaced/extended by swapping mapping tables
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* or adding per-signal handler functions.
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*/
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#include <linux/kernel.h>
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#include <linux/module.h>
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#include <linux/slab.h>
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#include <linux/usb.h>
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#include <linux/usb/input.h>
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#include <linux/input.h>
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#include <asm/unaligned.h>
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MODULE_AUTHOR("LLP group 32");
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MODULE_DESCRIPTION("Logitech G29 -> Media keys (USB driver)");
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MODULE_LICENSE("GPL");
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#define USB_VENDOR_ID_LOGITECH 0x046d
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#define USB_DEVICE_ID_LOGITECH_G29 0xc24f
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#define USB_DEVICE_ID_LOGITECH_G29_ALT 0xc260
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#define G29_REPORT_LEN 12
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/*
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* Button masks
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*/
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#define G29_BTN_PLUS 0x00800000u
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#define G29_BTN_MINUS 0x01000000u
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#define G29_BTN_RED_CW 0x02000000u
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#define G29_BTN_RED_CCW 0x04000000u
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#define G29_BTN_RETURN 0x08000000u
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#define G29_BTN_R1 0x00000100u
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#define G29_BTN_L1 0x00000200u
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enum g29_mode {
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G29_MODE_MEDIA = 0,
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};
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static int mode = G29_MODE_MEDIA;
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module_param(mode, int, 0444);
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MODULE_PARM_DESC(mode, "Mapping mode (0=MEDIA)");
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struct g29_state {
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u32 buttons;
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u16 rot;
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u8 gas;
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u8 brk;
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u8 clt;
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u8 grx;
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u8 gry;
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u8 grz;
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};
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/*
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* Mapping table entry
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*/
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struct g29_keymap_edge {
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u32 mask;
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unsigned short keycode;
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};
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static const struct g29_keymap_edge g29_media_edge_map[] = {
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/* Red rotary = volume */
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{ G29_BTN_RED_CW, KEY_VOLUMEUP },
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{ G29_BTN_RED_CCW, KEY_VOLUMEDOWN },
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/* Return = play/pause */
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{ G29_BTN_RETURN, KEY_PLAYPAUSE },
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/* Plus/Minus = next/prev */
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{ G29_BTN_R1, KEY_NEXTSONG },
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{ G29_BTN_L1, KEY_PREVIOUSSONG },
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};
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struct g29_dev {
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char name[128];
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char phys[64];
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struct usb_device *udev;
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struct input_dev *input;
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struct urb *urb;
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u8 *buf;
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dma_addr_t buf_dma;
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struct g29_state last;
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};
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/* Parsing */
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static bool g29_parse_report(struct g29_state *out, const u8 *data, int len)
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{
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if (len < G29_REPORT_LEN)
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return false;
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/* bytes 0..3 buttons bitfield */
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out->buttons = get_unaligned_le32(&data[0]);
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/* bytes 4..5 rotation */
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out->rot = get_unaligned_le16(&data[4]);
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out->gas = data[6];
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out->brk = data[7];
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out->clt = data[8];
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out->grx = data[9];
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out->gry = data[10];
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out->grz = data[11];
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return true;
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}
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/* Mapping policy */
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static void g29_pulse_key(struct input_dev *input, unsigned short keycode)
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{
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/* A pulse is a press+release within one report frame. */
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input_report_key(input, keycode, 1);
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input_report_key(input, keycode, 0);
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}
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static void g29_apply_media_mode(struct g29_dev *g29,
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const struct g29_state *prev,
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const struct g29_state *cur)
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{
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u32 pressed = cur->buttons & ~prev->buttons;
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size_t i;
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for (i = 0; i < ARRAY_SIZE(g29_media_edge_map); i++) {
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const struct g29_keymap_edge *e = &g29_media_edge_map[i];
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if (pressed & e->mask)
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g29_pulse_key(g29->input, e->keycode);
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}
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input_sync(g29->input);
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}
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static void g29_process_report(struct g29_dev *g29, const u8 *data, int len)
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{
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struct g29_state cur;
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if (!g29_parse_report(&cur, data, len))
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return;
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switch (mode) {
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case G29_MODE_MEDIA:
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default:
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g29_apply_media_mode(g29, &g29->last, &cur);
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break;
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}
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g29->last = cur;
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}
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/* URB plumbing */
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static void g29_urb_complete(struct urb *urb)
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{
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struct g29_dev *g29 = urb->context;
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int ret;
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switch (urb->status) {
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case 0:
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break; /* success */
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case -ECONNRESET:
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case -ENOENT:
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case -ESHUTDOWN:
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return; /* cancelled/disconnected */
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default:
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goto resubmit; /* transient error */
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}
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g29_process_report(g29, g29->buf, urb->actual_length);
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resubmit:
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ret = usb_submit_urb(urb, GFP_ATOMIC);
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if (ret)
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dev_err(&g29->udev->dev, "usb_submit_urb failed: %d\n", ret);
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}
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static int g29_input_open(struct input_dev *input)
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{
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struct g29_dev *g29 = input_get_drvdata(input);
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g29->urb->dev = g29->udev;
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if (usb_submit_urb(g29->urb, GFP_KERNEL))
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return -EIO;
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return 0;
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}
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static void g29_input_close(struct input_dev *input)
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{
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struct g29_dev *g29 = input_get_drvdata(input);
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usb_kill_urb(g29->urb);
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}
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/* USB driver binding */
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static int g29_probe(struct usb_interface *intf, const struct usb_device_id *id)
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{
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struct usb_device *udev = interface_to_usbdev(intf);
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struct usb_host_interface *alts = intf->cur_altsetting;
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struct usb_endpoint_descriptor *ep = NULL;
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struct g29_dev *g29;
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struct input_dev *input;
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int i, pipe, maxp, error;
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/* Find an interrupt IN endpoint capable of carrying the 12-byte report. */
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for (i = 0; i < alts->desc.bNumEndpoints; i++) {
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struct usb_endpoint_descriptor *cand = &alts->endpoint[i].desc;
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if (!usb_endpoint_is_int_in(cand))
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continue;
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pipe = usb_rcvintpipe(udev, cand->bEndpointAddress);
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maxp = usb_maxpacket(udev, pipe);
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if (maxp >= G29_REPORT_LEN) {
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ep = cand;
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break;
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}
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}
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if (!ep)
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return -ENODEV;
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g29 = kzalloc(sizeof(*g29), GFP_KERNEL);
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if (!g29)
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return -ENOMEM;
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input = input_allocate_device();
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if (!input) {
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error = -ENOMEM;
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goto err_free_g29;
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}
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g29->udev = udev;
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g29->input = input;
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memset(&g29->last, 0, sizeof(g29->last));
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/* Allocate a fixed-size report buffer (12 bytes). */
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g29->buf = usb_alloc_coherent(udev, G29_REPORT_LEN, GFP_KERNEL, &g29->buf_dma);
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if (!g29->buf) {
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error = -ENOMEM;
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goto err_free_input;
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}
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g29->urb = usb_alloc_urb(0, GFP_KERNEL);
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if (!g29->urb) {
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error = -ENOMEM;
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goto err_free_buf;
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}
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/* Build a friendly input device name. */
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if (udev->manufacturer)
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strscpy(g29->name, udev->manufacturer, sizeof(g29->name));
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if (udev->product) {
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if (udev->manufacturer)
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strlcat(g29->name, " ", sizeof(g29->name));
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strlcat(g29->name, udev->product, sizeof(g29->name));
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}
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if (!strlen(g29->name))
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snprintf(g29->name, sizeof(g29->name),
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"Logitech G29 Media %04x:%04x",
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le16_to_cpu(udev->descriptor.idVendor),
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le16_to_cpu(udev->descriptor.idProduct));
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usb_make_path(udev, g29->phys, sizeof(g29->phys));
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strlcat(g29->phys, "/input0", sizeof(g29->phys));
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input->name = g29->name;
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input->phys = g29->phys;
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usb_to_input_id(udev, &input->id);
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input->dev.parent = &intf->dev;
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__set_bit(EV_KEY, input->evbit);
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/* Advertise only the keys we emit in media mode. */
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input_set_capability(input, EV_KEY, KEY_VOLUMEUP);
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input_set_capability(input, EV_KEY, KEY_VOLUMEDOWN);
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input_set_capability(input, EV_KEY, KEY_PLAYPAUSE);
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input_set_capability(input, EV_KEY, KEY_NEXTSONG);
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input_set_capability(input, EV_KEY, KEY_PREVIOUSSONG);
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input_set_drvdata(input, g29);
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input->open = g29_input_open;
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input->close = g29_input_close;
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pipe = usb_rcvintpipe(udev, ep->bEndpointAddress);
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usb_fill_int_urb(g29->urb, udev, pipe,
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g29->buf, G29_REPORT_LEN,
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g29_urb_complete, g29, ep->bInterval);
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g29->urb->transfer_dma = g29->buf_dma;
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g29->urb->transfer_flags |= URB_NO_TRANSFER_DMA_MAP;
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error = input_register_device(input);
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if (error)
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goto err_free_urb;
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usb_set_intfdata(intf, g29);
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dev_info(&intf->dev,
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"G29 media driver bound (ep=%02x interval=%u)\n",
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ep->bEndpointAddress, ep->bInterval);
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return 0;
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err_free_urb:
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usb_free_urb(g29->urb);
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err_free_buf:
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usb_free_coherent(udev, G29_REPORT_LEN, g29->buf, g29->buf_dma);
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err_free_input:
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input_free_device(input);
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err_free_g29:
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kfree(g29);
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return error;
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}
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static void g29_disconnect(struct usb_interface *intf)
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{
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struct g29_dev *g29 = usb_get_intfdata(intf);
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usb_set_intfdata(intf, NULL);
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if (!g29)
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return;
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usb_kill_urb(g29->urb);
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input_unregister_device(g29->input);
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usb_free_urb(g29->urb);
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usb_free_coherent(interface_to_usbdev(intf), G29_REPORT_LEN,
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g29->buf, g29->buf_dma);
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kfree(g29);
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dev_info(&intf->dev, "G29 media driver disconnected\n");
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}
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static const struct usb_device_id g29_id_table[] = {
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{ USB_DEVICE(USB_VENDOR_ID_LOGITECH, USB_DEVICE_ID_LOGITECH_G29) },
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{ USB_DEVICE(USB_VENDOR_ID_LOGITECH, USB_DEVICE_ID_LOGITECH_G29_ALT) },
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{ }
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};
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MODULE_DEVICE_TABLE(usb, g29_id_table);
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static struct usb_driver g29_driver = {
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.name = "g29_media_usb",
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.probe = g29_probe,
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.disconnect = g29_disconnect,
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.id_table = g29_id_table,
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};
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module_usb_driver(g29_driver);
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