/* SPDX-License-Identifier: GPL-2.0 */ #ifndef __842_H__ #define __842_H__ /* The 842 compressed format is made up of multiple blocks, each of * which have the format: * * <template>[arg1][arg2][arg3][arg4] * * where there are between 0 and 4 template args, depending on the specific * template operation. For normal operations, each arg is either a specific * number of data bytes to add to the output buffer, or an index pointing * to a previously-written number of data bytes to copy to the output buffer. * * The template code is a 5-bit value. This code indicates what to do with * the following data. Template codes from 0 to 0x19 should use the template * table, the static "decomp_ops" table used in decompress. For each template * (table row), there are between 1 and 4 actions; each action corresponds to * an arg following the template code bits. Each action is either a "data" * type action, or a "index" type action, and each action results in 2, 4, or 8 * bytes being written to the output buffer. Each template (i.e. all actions * in the table row) will add up to 8 bytes being written to the output buffer. * Any row with less than 4 actions is padded with noop actions, indicated by * N0 (for which there is no corresponding arg in the compressed data buffer). * * "Data" actions, indicated in the table by D2, D4, and D8, mean that the * corresponding arg is 2, 4, or 8 bytes, respectively, in the compressed data * buffer should be copied directly to the output buffer. * * "Index" actions, indicated in the table by I2, I4, and I8, mean the * corresponding arg is an index parameter that points to, respectively, a 2, * 4, or 8 byte value already in the output buffer, that should be copied to * the end of the output buffer. Essentially, the index points to a position * in a ring buffer that contains the last N bytes of output buffer data. * The number of bits for each index's arg are: 8 bits for I2, 9 bits for I4, * and 8 bits for I8. Since each index points to a 2, 4, or 8 byte section, * this means that I2 can reference 512 bytes ((2^8 bits = 256) * 2 bytes), I4 * can reference 2048 bytes ((2^9 = 512) * 4 bytes), and I8 can reference 2048 * bytes ((2^8 = 256) * 8 bytes). Think of it as a kind-of ring buffer for * each of I2, I4, and I8 that are updated for each byte written to the output * buffer. In this implementation, the output buffer is directly used for each * index; there is no additional memory required. Note that the index is into * a ring buffer, not a sliding window; for example, if there have been 260 * bytes written to the output buffer, an I2 index of 0 would index to byte 256 * in the output buffer, while an I2 index of 16 would index to byte 16 in the * output buffer. * * There are also 3 special template codes; 0x1b for "repeat", 0x1c for * "zeros", and 0x1e for "end". The "repeat" operation is followed by a 6 bit * arg N indicating how many times to repeat. The last 8 bytes written to the * output buffer are written again to the output buffer, N + 1 times. The * "zeros" operation, which has no arg bits, writes 8 zeros to the output * buffer. The "end" operation, which also has no arg bits, signals the end * of the compressed data. There may be some number of padding (don't care, * but usually 0) bits after the "end" operation bits, to fill the buffer * length to a specific byte multiple (usually a multiple of 8, 16, or 32 * bytes). * * This software implementation also uses one of the undefined template values, * 0x1d as a special "short data" template code, to represent less than 8 bytes * of uncompressed data. It is followed by a 3 bit arg N indicating how many * data bytes will follow, and then N bytes of data, which should be copied to * the output buffer. This allows the software 842 compressor to accept input * buffers that are not an exact multiple of 8 bytes long. However, those * compressed buffers containing this sw-only template will be rejected by * the 842 hardware decompressor, and must be decompressed with this software * library. The 842 software compression module includes a parameter to * disable using this sw-only "short data" template, and instead simply * reject any input buffer that is not a multiple of 8 bytes long. * * After all actions for each operation code are processed, another template * code is in the next 5 bits. The decompression ends once the "end" template * code is detected. */ #include <linux/module.h> #include <linux/kernel.h> #include <linux/bitops.h> #include <linux/crc32.h> #include <asm/unaligned.h> #include <linux/sw842.h> /* special templates */ #define OP_REPEAT … #define OP_ZEROS … #define OP_END … /* sw only template - this is not in the hw design; it's used only by this * software compressor and decompressor, to allow input buffers that aren't * a multiple of 8. */ #define OP_SHORT_DATA … /* additional bits of each op param */ #define OP_BITS … #define REPEAT_BITS … #define SHORT_DATA_BITS … #define I2_BITS … #define I4_BITS … #define I8_BITS … #define CRC_BITS … #define REPEAT_BITS_MAX … #define SHORT_DATA_BITS_MAX … /* Arbitrary values used to indicate action */ #define OP_ACTION … #define OP_ACTION_INDEX … #define OP_ACTION_DATA … #define OP_ACTION_NOOP … #define OP_AMOUNT … #define OP_AMOUNT_0 … #define OP_AMOUNT_2 … #define OP_AMOUNT_4 … #define OP_AMOUNT_8 … #define D2 … #define D4 … #define D8 … #define I2 … #define I4 … #define I8 … #define N0 … /* the max of the regular templates - not including the special templates */ #define OPS_MAX … #endif
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