pkarashchenko commented on issue #6569:
URL:
https://github.com/apache/incubator-nuttx/issues/6569#issuecomment-1173733406
@xiaoxiang781216 the issue is that currently it is implemented as you
pointed, but it use `lr`/`sc`, but I posted an issue that we can rework it to
use `amoswap`.
Current code:
```
.globl up_testset
.type up_testset, %function
up_testset:
li a1, SP_LOCKED
/* Test if the spinlock is locked or not */
retry:
LR_INST a2, (a0) /* Test if spinlock is locked or not */
beq a2, a1, locked /* Already locked? Go to locked: */
/* Not locked ... attempt to lock it */
SC_INST a2, a1, (a0) /* Attempt to set the locked state (a1) to (a0) */
bnez a2, retry /* a2 will not be zero, if sc.b failed, try again
*/
/* Lock acquired -- return SP_UNLOCKED */
fence /* Required before accessing protected resource */
li a0, SP_UNLOCKED
jr ra
/* Lock not acquired -- return SP_LOCKED */
locked:
li a0, SP_LOCKED
jr ra
.size up_testset, . - up_testset
.end
```
But can be something like
```
.globl up_testset
.type up_testset, %function
up_testset:
li a1, SP_LOCKED
amoswap.w a2, a1, (a0) /* Attempt to acquire spinlock atomically */
beq a2, a1, locked /* Already locked? Go to locked: */
/* Lock acquired -- return SP_UNLOCKED */
fence /* Required before accessing protected resource */
li a0, SP_UNLOCKED
jr ra
/* Lock not acquired -- return SP_LOCKED */
locked:
li a0, SP_LOCKED
jr ra
.size up_testset, . - up_testset
.end
```
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