gpio: stm32: Use atomic set/reset in stm32_gpio_set()
The current implementation of stm32_gpio_set() uses the GPIO output data
register to change the state of individual GPIOs. The generated
assembler needs at least 3 instructions: load / modify / store.
This opens a small race window, for example if a thread and an
interrupt both try to change the state of the same GPIO bank.
Use the GPIO bit set/reset register to perform the atomic change without
locking.
This also has the benefit of a more optimised implementation, which can
be useful for GPIO-intensive work. Compare the new version:
08000c98 <stm32_gpio_set>:
8000c98: f001 010f and.w r1, r1, #15
8000c9c: 2301 movs r3, #1
8000c9e: b902 cbnz r2, 8000ca2 <stm32_gpio_set+0xa>
8000ca0: 3110 adds r1, #16
8000ca2: 408b lsls r3, r1
8000ca4: 6183 str r3, [r0, #24]
8000ca6: 2000 movs r0, #0
8000ca8: 4770 bx lr
and the old one:
08000c98 <stm32_gpio_set>:
8000c98: 2301 movs r3, #1
8000c9a: f001 010f and.w r1, r1, #15
8000c9e: fa03 f101 lsl.w r1, r3, r1
8000ca2: 6943 ldr r3, [r0, #20]
8000ca4: b10a cbz r2, 8000caa <stm32_gpio_set+0x12>
8000ca6: 4319 orrs r1, r3
8000ca8: e001 b.n 8000cae <stm32_gpio_set+0x16>
8000caa: ea23 0101 bic.w r1, r3, r1
8000cae: 6141 str r1, [r0, #20]
8000cb0: 2000 movs r0, #0
8000cb2: 4770 bx lr
Change-Id: Ie5800d1c345016028d1b9a099f5d74cac35f592a
Signed-off-by: Florian Vaussard <florian.vaussard@heig-vd.ch>
1 file changed
