[PATCH] irqchip/stm32mp-exti: fix the unit of the hwspinlock timeout

[PATCH] irqchip/stm32mp-exti: fix the unit of the hwspinlock timeout

[Ju Nan]

HWSPNLCK_TIMEOUT is passed to hwspin_lock_timeout_in_atomic(), whose
timeout argument is in milliseconds, not microseconds:

  atomic_delay += HWSPINLOCK_RETRY_DELAY_US;
  if (atomic_delay > to * 1000)
          return -ETIMEDOUT;

So stm32mp_exti_set_type() asks for a 1 second timeout where the comment
next to the macro says it wants 1 millisecond. The semaphore is polled
with udelay() from a section that holds chip_data->rlock, a
raw_spinlock_t, so preemption stays disabled for the whole wait on every
configuration, PREEMPT_RT included.

The hwspinlock core documents this explicitly:

  If the mode is HWLOCK_IN_ATOMIC (called from an atomic context) the
  timeout is handled with busy-waiting delays, hence shall not exceed
  few msecs.

Pass the value the comment always described. The core retries every
HWSPINLOCK_RETRY_DELAY_US (100 us), so the semaphore is still polled ten
times before giving up, which is far longer than any plausible hold time
on the coprocessor side. A timeout is reported with pr_err() and fails
the trigger type configuration, so shortening it degrades gracefully.

Signed-off-by: Ju Nan <junan76@163.com>
---
 drivers/irqchip/irq-stm32mp-exti.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/irqchip/irq-stm32mp-exti.c b/drivers/irqchip/irq-stm32mp-exti.c
index a24f4f1a4..f5f0109bf 100644
--- a/drivers/irqchip/irq-stm32mp-exti.c
+++ b/drivers/irqchip/irq-stm32mp-exti.c
@@ -23,7 +23,7 @@
 
 #define IRQS_PER_BANK			32
 
-#define HWSPNLCK_TIMEOUT		1000 /* usec */
+#define HWSPNLCK_TIMEOUT		1 /* msec */
 
 #define EXTI_EnCIDCFGR(n)		(0x180 + (n) * 4)
 #define EXTI_HWCFGR1			0x3f0
-- 
2.55.0