[PATCH v2 1/2] spi: cadence-quadspi: Prevent lost complete() call during indirect read

[Mateusz Litwin via B4 Relay <devnull+mateusz.litwin.nokia.com@kernel.org>]

From: Mateusz Litwin <mateusz.litwin@nokia.com>

A race condition exists between the read loop and IRQ `complete()` call.
An interrupt could call the complete() between the inner loop and
reinit_completion(), potentially losing the completion event and causing
an unnecessary timeout. Moving reinit_completion() before the loop
prevents this. A premature signal will only result in a spurious wakeup
and another wait cycle, which is preferable to waiting for a timeout.

Signed-off-by: Mateusz Litwin <mateusz.litwin@nokia.com>
---
 drivers/spi/spi-cadence-quadspi.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/drivers/spi/spi-cadence-quadspi.c b/drivers/spi/spi-cadence-quadspi.c
index a390b1815fde..02d1ff53e61d 100644
--- a/drivers/spi/spi-cadence-quadspi.c
+++ b/drivers/spi/spi-cadence-quadspi.c
@@ -769,6 +769,7 @@ static int cqspi_indirect_read_execute(struct cqspi_flash_pdata *f_pdata,
 	readl(reg_base + CQSPI_REG_INDIRECTRD); /* Flush posted write. */
 
 	while (remaining > 0) {
+		ret = 0;
 		if (use_irq &&
 		    !wait_for_completion_timeout(&cqspi->transfer_complete,
 						 msecs_to_jiffies(CQSPI_READ_TIMEOUT_MS)))
@@ -781,6 +782,14 @@ static int cqspi_indirect_read_execute(struct cqspi_flash_pdata *f_pdata,
 		if (cqspi->slow_sram)
 			writel(0x0, reg_base + CQSPI_REG_IRQMASK);
 
+		/*
+		 * Prevent lost interrupt and race condition by reinitializing early.
+		 * A spurious wakeup and another wait cycle can occur here,
+		 * which is preferable to waiting until timeout if interrupt is lost.
+		 */
+		if (use_irq)
+			reinit_completion(&cqspi->transfer_complete);
+
 		bytes_to_read = cqspi_get_rd_sram_level(cqspi);
 
 		if (ret && bytes_to_read == 0) {
@@ -813,7 +822,6 @@ static int cqspi_indirect_read_execute(struct cqspi_flash_pdata *f_pdata,
 		}
 
 		if (use_irq && remaining > 0) {
-			reinit_completion(&cqspi->transfer_complete);
 			if (cqspi->slow_sram)
 				writel(CQSPI_REG_IRQ_WATERMARK, reg_base + CQSPI_REG_IRQMASK);
 		}

-- 
2.43.0