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8 * Isolate your NEON code in a separate compilation unit, and compile it with
10 * Put kernel_neon_begin() and kernel_neon_end() calls around the calls into your
12 * Don't sleep in your NEON code, and be aware that it will be executed with
18 It is possible to use NEON instructions (and in some cases, VFP instructions) in
20 register file is not preserved and restored at every context switch or taken
27 Lazy preserve and restore
29 The NEON/VFP register file is managed using lazy preserve (on UP systems) and
30 lazy restore (on both SMP and UP systems). This means that the register file is
31 kept 'live', and is only preserved and restored when multiple tasks are
35 instruction is issued, allowing the kernel to step in and perform the restore if
39 it is required to do an 'eager' preserve of the NEON/VFP register file, and
50 For reasons of performance and simplicity, it was decided that there shall be no
54 following rules and restrictions apply in the kernel:
60 kernel_neon_end() and kernel_neon_begin() in places in your code where none of
65 VFP and support code
70 exception. The kernel responds by inspecting the VFP control registers and the
71 current instruction and arguments, and emulates the instruction in software.
75 fail and generate an OOPS.
80 The compiler is not aware of the special significance of kernel_neon_begin() and
83 instructions of its own at -O3 level if -mfpu=neon is selected, and even if the
87 Therefore, the recommended and only supported way of using NEON/VFP in the
89 * isolate the NEON code in a separate compilation unit and compile it with
96 both NEON and VFP instructions will only ever appear in designated compilation
109 parallelism, and generates NEON code from ordinary C source code. This is fully