path: root/drivers/gpu/drm/drm_panic_qr.rs

// SPDX-License-Identifier: MIT

//! This is a simple QR encoder for DRM panic.
//!
//! It is called from a panic handler, so it should't allocate memory and
//! does all the work on the stack or on the provided buffers. For
//! simplification, it only supports low error correction, and applies the
//! first mask (checkerboard). It will draw the smallest QRcode that can
//! contain the string passed as parameter. To get the most compact
//! QR code, the start of the URL is encoded as binary, and the
//! compressed kmsg is encoded as numeric.
//!
//! The binary data must be a valid URL parameter, so the easiest way is
//! to use base64 encoding. But this wastes 25% of data space, so the
//! whole stack trace won't fit in the QR code. So instead it encodes
//! every 13bits of input into 4 decimal digits, and then uses the
//! efficient numeric encoding, that encode 3 decimal digits into
//! 10bits. This makes 39bits of compressed data into 12 decimal digits,
//! into 40bits in the QR code, so wasting only 2.5%. And the numbers are
//! valid URL parameter, so the website can do the reverse, to get the
//! binary data.
//!
//! Inspired by these 3 projects, all under MIT license:
//!
//! * <https://github.com/kennytm/qrcode-rust>
//! * <https://github.com/erwanvivien/fast_qr>
//! * <https://github.com/bjguillot/qr>

use core::cmp;
use kernel::str::CStr;

#[derive(Debug, Clone, Copy, PartialEq, Eq, Ord, PartialOrd)]
struct Version(usize);

// Generator polynomials for ECC, only those that are needed for low quality.
const P7: [u8; 7] = [87, 229, 146, 149, 238, 102, 21];
const P10: [u8; 10] = [251, 67, 46, 61, 118, 70, 64, 94, 32, 45];
const P15: [u8; 15] = [
    8, 183, 61, 91, 202, 37, 51, 58, 58, 237, 140, 124, 5, 99, 105,
];
const P18: [u8; 18] = [
    215, 234, 158, 94, 184, 97, 118, 170, 79, 187, 152, 148, 252, 179, 5, 98, 96, 153,
];
const P20: [u8; 20] = [
    17, 60, 79, 50, 61, 163, 26, 187, 202, 180, 221, 225, 83, 239, 156, 164, 212, 212, 188, 190,
];
const P22: [u8; 22] = [
    210, 171, 247, 242, 93, 230, 14, 109, 221, 53, 200, 74, 8, 172, 98, 80, 219, 134, 160, 105,
    165, 231,
];
const P24: [u8; 24] = [
    229, 121, 135, 48, 211, 117, 251, 126, 159, 180, 169, 152, 192, 226, 228, 218, 111, 0, 117,
    232, 87, 96, 227, 21,
];
const P26: [u8; 26] = [
    173, 125, 158, 2, 103, 182, 118, 17, 145, 201, 111, 28, 165, 53, 161, 21, 245, 142, 13, 102,
    48, 227, 153, 145, 218, 70,
];
const P28: [u8; 28] = [
    168, 223, 200, 104, 224, 234, 108, 180, 110, 190, 195, 147, 205, 27, 232, 201, 21, 43, 245, 87,
    42, 195, 212, 119, 242, 37, 9, 123,
];
const P30: [u8; 30] = [
    41, 173, 145, 152, 216, 31, 179, 182, 50, 48, 110, 86, 239, 96, 222, 125, 42, 173, 226, 193,
    224, 130, 156, 37, 251, 216, 238, 40, 192, 180,
];

/// QR Code parameters for Low quality ECC:
/// - Error Correction polynomial.
/// - Number of blocks in group 1.
/// - Number of blocks in group 2.
/// - Block size in group 1.
///
/// (Block size in group 2 is one more than group 1).
struct VersionParameter(&'static [u8], u8