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lib: sbi: Simplify wait_for_coldboot() implementation

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On QEMU virt machine with large number of HARTs, some of the HARTs
randomly fail to come out of wait_for_coldboot() due to one of the
following race-conditions:

1) Failing HARTs are not able to acquire the coldboot_lock and
   update the coldboot_hartmask in wait_for_coldboot() before
   the coldboot HART acquires the coldboot_lock and sends IPI
   in wake_coldboot_harts() hence the failing HARTs never
   receive IPI from the coldboot HART.

2) Failing HARTs acquire the coldbood_lock and update the
   coldboot_hartmask before coldboot HART does sbi_scratch_init()
   so the sbi_hartmask_set_hartid() does not update the
   coldboot_hartmask on the failing HARTs hence they never
   receive IPI from the coldboot HART.

To address this, use a simple busy-loop in wait_for_coldboot() for
polling on coldboot_done flag.

Signed-off-by: Anup Patel <apatel@ventanamicro.com>
This commit is contained in:
Anup Patel
2024-03-15 19:55:23 +05:30
committed by Anup Patel
parent f5375bc15e
commit beb0cd177f
2 changed files with 8 additions and 68 deletions
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6
include/sbi/riscv_barrier.h
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@@ -40,7 +40,11 @@
#define smp_wmb() RISCV_FENCE(w,w)
/* CPU relax for busy loop */
#define cpu_relax() asm volatile ("" : : : "memory")
#define cpu_relax() \
do { \
unsigned long __t; \
__asm__ __volatile__ ("div %0, %0, zero" : "=r" (__t)); \
} while (0)
/* clang-format on */