Documentation/core-api/packing.rst

6 -----------------
10 One can memory-map a pointer to a carefully crafted struct over the hardware
23 were performed byte-by-byte. Also the code can easily get cluttered, and the
24 high-level idea might get lost among the many bit shifts required.
25 Many drivers take the bit-shifting approach and then attempt to reduce the
30 ------------
34   - Packing a CPU-usable number into a memory buffer (with hardware
36   - Unpacking a memory buffer (which has hardware constraints/quirks)
37     into a CPU-usable number.
57   31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10  9  8  7  6  5  4  3  2  1  0
60 That is, the MSByte (7) of the CPU-usable u64 sits at memory offset 0, and the
73   24 25 26 27 28 29 30 31 16 17 18 19 20 21 22 23  8  9 10 11 12 13 14 15  0  1  2  3  4  5  6  7
86   7  6  5  4  3  2  1  0  15 14 13 12 11 10  9  8 23 22 21 20 19 18 17 16 31 30 29 28 27 26 25 24
90 byte from each 4-byte word is placed at its mirrored position compared to
100   0  1  2  3  4  5  6  7  8   9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
108   31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10  9  8  7  6  5  4  3  2  1  0
114 4 bytes correspond to the least significant 4-byte word, next 4 bytes to
115 the more significant 4-byte word.
123   24 25 26 27 28 29 30 31 16 17 18 19 20 21 22 23  8  9 10 11 12 13 14 15  0  1  2  3  4  5  6  7
134   7  6  5  4  3  2  1  0  15 14 13 12 11 10  9  8 23 22 21 20 19 18 17 16 31 30 29 28 27 26 25 24
145   0  1  2  3  4  5  6  7  8   9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
155 ------------
160 xxx_packing() that calls it using the proper QUIRK_* one-hot bits set.
162 The packing() function returns an int-encoded error code, which protects the