| Message ID | 20240402014706.3969151-2-harisokn@amazon.com |
|---|---|
| State | Superseded |
| Headers | show |
| Series | [1/3] arm64: Add TIF_POLLING_NRFLAG | expand |
From: Haris Okanovic > Sent: 02 April 2024 02:47 > > Perform an exclusive load, which atomically loads a word and arms the > execusive monitor to enable wfe() polling of an address. > > Adding this macro in preparation for an arm64 cpuidle driver which > supports a wfe() based polling state. > > https://developer.arm.com/documentation/dht0008/a/arm-synchronization-primitives/exclusive- > accesses/exclusive-monitors > > Signed-off-by: Haris Okanovic <harisokn@amazon.com> > --- > arch/arm64/include/asm/readex.h | 46 +++++++++++++++++++++++++++++++++ > 1 file changed, 46 insertions(+) > create mode 100644 arch/arm64/include/asm/readex.h > > diff --git a/arch/arm64/include/asm/readex.h b/arch/arm64/include/asm/readex.h > new file mode 100644 > index 000000000000..51963c3107e1 > --- /dev/null > +++ b/arch/arm64/include/asm/readex.h > @@ -0,0 +1,46 @@ > +/* SPDX-License-Identifier: GPL-2.0 */ > +/* > + * Based on arch/arm64/include/asm/rwonce.h > + * > + * Copyright (C) 2020 Google LLC. > + * Copyright (C) 2024 Amazon.com, Inc. or its affiliates. > + */ > + > +#ifndef __ASM_READEX_H > +#define __ASM_READEX_H > + > +#define __LOAD_EX(sfx, regs...) "ldaxr" #sfx "\t" #regs > + > +#define __READ_ONCE_EX(x) \ > +({ \ > + typeof(&(x)) __x = &(x); \ > + int atomic = 1; \ > + union { __unqual_scalar_typeof(*__x) __val; char __c[1]; } __u; \ > + switch (sizeof(x)) { \ > + case 1: \ > + asm volatile(__LOAD_EX(b, %w0, %1) \ > + : "=r" (*(__u8 *)__u.__c) \ > + : "Q" (*__x) : "memory"); \ > + break; \ > + case 2: \ > + asm volatile(__LOAD_EX(h, %w0, %1) \ > + : "=r" (*(__u16 *)__u.__c) \ > + : "Q" (*__x) : "memory"); \ > + break; \ > + case 4: \ > + asm volatile(__LOAD_EX(, %w0, %1) \ > + : "=r" (*(__u32 *)__u.__c) \ > + : "Q" (*__x) : "memory"); \ > + break; \ > + case 8: \ > + asm volatile(__LOAD_EX(, %0, %1) \ > + : "=r" (*(__u64 *)__u.__c) \ > + : "Q" (*__x) : "memory"); \ > + break; \ > + default: \ > + atomic = 0; \ > + } \ > + atomic ? (typeof(*__x))__u.__val : (*(volatile typeof(__x))__x);\ I'm pretty sure that doesn't work the way you expect. The ?: operator promotes 'unsigned char' to 'int'. So you can fall foul of signedness tests (eg in min()). It also isn't going to work for non-scalers. Replacing the ?: with __builtin_choose_expr() may help. (This is probably a bug in the code you copied.) David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
diff --git a/arch/arm64/include/asm/readex.h b/arch/arm64/include/asm/readex.h new file mode 100644 index 000000000000..51963c3107e1 --- /dev/null +++ b/arch/arm64/include/asm/readex.h @@ -0,0 +1,46 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +/* + * Based on arch/arm64/include/asm/rwonce.h + * + * Copyright (C) 2020 Google LLC. + * Copyright (C) 2024 Amazon.com, Inc. or its affiliates. + */ + +#ifndef __ASM_READEX_H +#define __ASM_READEX_H + +#define __LOAD_EX(sfx, regs...) "ldaxr" #sfx "\t" #regs + +#define __READ_ONCE_EX(x) \ +({ \ + typeof(&(x)) __x = &(x); \ + int atomic = 1; \ + union { __unqual_scalar_typeof(*__x) __val; char __c[1]; } __u; \ + switch (sizeof(x)) { \ + case 1: \ + asm volatile(__LOAD_EX(b, %w0, %1) \ + : "=r" (*(__u8 *)__u.__c) \ + : "Q" (*__x) : "memory"); \ + break; \ + case 2: \ + asm volatile(__LOAD_EX(h, %w0, %1) \ + : "=r" (*(__u16 *)__u.__c) \ + : "Q" (*__x) : "memory"); \ + break; \ + case 4: \ + asm volatile(__LOAD_EX(, %w0, %1) \ + : "=r" (*(__u32 *)__u.__c) \ + : "Q" (*__x) : "memory"); \ + break; \ + case 8: \ + asm volatile(__LOAD_EX(, %0, %1) \ + : "=r" (*(__u64 *)__u.__c) \ + : "Q" (*__x) : "memory"); \ + break; \ + default: \ + atomic = 0; \ + } \ + atomic ? (typeof(*__x))__u.__val : (*(volatile typeof(__x))__x);\ +}) + +#endif
Perform an exclusive load, which atomically loads a word and arms the execusive monitor to enable wfe() polling of an address. Adding this macro in preparation for an arm64 cpuidle driver which supports a wfe() based polling state. https://developer.arm.com/documentation/dht0008/a/arm-synchronization-primitives/exclusive-accesses/exclusive-monitors Signed-off-by: Haris Okanovic <harisokn@amazon.com> --- arch/arm64/include/asm/readex.h | 46 +++++++++++++++++++++++++++++++++ 1 file changed, 46 insertions(+) create mode 100644 arch/arm64/include/asm/readex.h