diff options
Diffstat (limited to 'arch/arm64/include/asm/assembler.h')
| -rw-r--r-- | arch/arm64/include/asm/assembler.h | 73 |
1 files changed, 73 insertions, 0 deletions
diff --git a/arch/arm64/include/asm/assembler.h b/arch/arm64/include/asm/assembler.h index fe2ff3efe1f0..0bcc98dbba56 100644 --- a/arch/arm64/include/asm/assembler.h +++ b/arch/arm64/include/asm/assembler.h @@ -628,4 +628,77 @@ USER(\label, ic ivau, \tmp2) // invalidate I line PoU .endif .endm +/* + * Check whether to yield to another runnable task from kernel mode NEON code + * (which runs with preemption disabled). + * + * if_will_cond_yield_neon + * // pre-yield patchup code + * do_cond_yield_neon + * // post-yield patchup code + * endif_yield_neon <label> + * + * where <label> is optional, and marks the point where execution will resume + * after a yield has been performed. If omitted, execution resumes right after + * the endif_yield_neon invocation. Note that the entire sequence, including + * the provided patchup code, will be omitted from the image if CONFIG_PREEMPT + * is not defined. + * + * As a convenience, in the case where no patchup code is required, the above + * sequence may be abbreviated to + * + * cond_yield_neon <label> + * + * Note that the patchup code does not support assembler directives that change + * the output section, any use of such directives is undefined. + * + * The yield itself consists of the following: + * - Check whether the preempt count is exactly 1, in which case disabling + * preemption once will make the task preemptible. If this is not the case, + * yielding is pointless. + * - Check whether TIF_NEED_RESCHED is set, and if so, disable and re-enable + * kernel mode NEON (which will trigger a reschedule), and branch to the + * yield fixup code. + * + * This macro sequence may clobber all CPU state that is not guaranteed by the + * AAPCS to be preserved across an ordinary function call. + */ + + .macro cond_yield_neon, lbl + if_will_cond_yield_neon + do_cond_yield_neon + endif_yield_neon \lbl + .endm + + .macro if_will_cond_yield_neon +#ifdef CONFIG_PREEMPT + get_thread_info x0 + ldr w1, [x0, #TSK_TI_PREEMPT] + ldr x0, [x0, #TSK_TI_FLAGS] + cmp w1, #PREEMPT_DISABLE_OFFSET + csel x0, x0, xzr, eq + tbnz x0, #TIF_NEED_RESCHED, .Lyield_\@ // needs rescheduling? + /* fall through to endif_yield_neon */ + .subsection 1 +.Lyield_\@ : +#else + .section ".discard.cond_yield_neon", "ax" +#endif + .endm + + .macro do_cond_yield_neon + bl kernel_neon_end + bl kernel_neon_begin + .endm + + .macro endif_yield_neon, lbl + .ifnb \lbl + b \lbl + .else + b .Lyield_out_\@ + .endif + .previous +.Lyield_out_\@ : + .endm + #endif /* __ASM_ASSEMBLER_H */ |