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lib: sbi: Apply budget restriction when polling Zkr CSR state transition

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Zkr architecture doesn't define a time limit on state transitions
which results in hanging on unresponsive or event-driven platforms.
To prevent this, we need to limit polling iterations and fall back
in case the budget is over, and stack guard keeps its initial value.
The budget is configurable with CONFIG_ZKR_POLL_BUDGET, defaulting
to 1000 iterations. Successful reads do not consume a try.

Signed-off-by: Evgeny Voevodin <evvoevod@tenstorrent.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
Link: https://lore.kernel.org/r/20260519225014.244672-1-evvoevod@tenstorrent.com
Signed-off-by: Anup Patel <anup@brainfault.org>
This commit is contained in:
Evgeny Voevodin
2026-05-19 22:50:14 +00:00
committed by Anup Patel
parent ecc92e87a9
commit e134d52106
2 changed files with 21 additions and 3 deletions
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lib/sbi/sbi_init.c
+9 -3
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@@ -280,20 +280,26 @@ static void __noreturn init_coldboot(struct sbi_scratch *scratch, u32 hartid)
if (sbi_hart_has_extension(scratch, SBI_HART_EXT_ZKR)) {
unsigned long guard_val = 0;
int chunks = sizeof(unsigned long) / sizeof(uint16_t);
bool res = true;
unsigned int tries = CONFIG_ZKR_POLL_BUDGET;
bool res = false;
while (chunks) {
while (chunks && tries) {
unsigned long seed = csr_swap(CSR_SEED, 0);
unsigned long opst = seed & SEED_OPTS_MASK;
res = false;
if (opst == SEED_OPTS_DEAD) {
res = false;
break;
}
if (opst == SEED_OPTS_ES16) {
guard_val = (guard_val << 16) | (seed & SEED_ENTROPY_MASK);
chunks--;
res = true;
/* Successful read doesn't consume a try */
tries++;
}
tries--;
continue;
}
if (res)