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Subject[PATCH v2 15/17] arm64: Add test_and_clear_flag and set_flag atomic assembler primitives
Date
As we're about to need to atomically manipulate some thread
flags from entry.S, let's introduce two atomic primitives
(test_and_clear_flag and set_flag) for that purpose.

We provide two implementations: one using the traditional
LL/SC instructions, and one using the ARMv8.1 atomics.

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
---
arch/arm64/include/asm/assembler.h | 37 +++++++++++++++++++++++++++++++++++++
1 file changed, 37 insertions(+)

diff --git a/arch/arm64/include/asm/assembler.h b/arch/arm64/include/asm/assembler.h
index 0bcc98dbba56..d3612ad8035e 100644
--- a/arch/arm64/include/asm/assembler.h
+++ b/arch/arm64/include/asm/assembler.h
@@ -26,6 +26,7 @@
#include <asm/asm-offsets.h>
#include <asm/cpufeature.h>
#include <asm/debug-monitors.h>
+#include <asm/lse.h>
#include <asm/page.h>
#include <asm/pgtable-hwdef.h>
#include <asm/ptrace.h>
@@ -701,4 +702,40 @@ USER(\label, ic ivau, \tmp2) // invalidate I line PoU
.Lyield_out_\@ :
.endm

+/*
+ * test_and_clear_flag:
+ *
+ * res: register containing the result (0 or 1 << bitnum)
+ * addr: address of the word to be manipulated
+ * bitnum: number of the bit in that word
+ * wtmp: temporary register, must be a 32bit reg
+ */
+ .macro test_and_clear_flag, res, addr, bitnum, wtmp
+alt_lse " prfm pstl1strm, [\addr]", "nop"
+alt_lse "8:ldxr \res, [\addr]", "ldr \res, [\addr]"
+ tbz \res, #\bitnum, 9f
+alt_lse " bic \res, \res, #(1 << \bitnum)", "mov \res, #(1 << \bitnum)"
+alt_lse " stlxr \wtmp, \res, [\addr]", "ldclral \res, \res, [\addr]"
+alt_lse " cbnz \wtmp, 8b", "nop"
+alt_lse " dmb ish", "nop"
+alt_lse " orr \res, \res, #(1 << \bitnum)", "nop"
+9:
+ .endm
+
+/*
+ * set_flag:
+ *
+ * addr: address of the word to be manipulated
+ * bitnum: number of the bit in that word
+ * tmp: temporary register
+ * wtmp: temporary register, must be a 32bit reg
+ */
+ .macro set_flag, addr, bitnum, tmp, wtmp
+alt_lse " prfm pstl1strm, [\addr]", "mov \tmp, #(1 << \bitnum)"
+alt_lse "8:ldxr \tmp, [\addr]", "stset \tmp, [\addr]"
+alt_lse " orr \tmp, \tmp, #(1 << \bitnum)", "nop"
+alt_lse " stxr \wtmp, \tmp, [\addr]", "nop"
+alt_lse " cbnz \wtmp, 8b", "nop"
+ .endm
+
#endif /* __ASM_ASSEMBLER_H */
--
2.14.2
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