[PATCH v2 1/6] spi: tegra210-quad: Return IRQ_HANDLED when timeout already processed transfer

[Breno Leitao <leitao@debian.org>]

When the ISR thread wakes up late and finds that the timeout handler
has already processed the transfer (curr_xfer is NULL), return
IRQ_HANDLED instead of IRQ_NONE.

Use a similar approach to tegra_qspi_handle_timeout() by reading
QSPI_TRANS_STATUS and checking the QSPI_RDY bit to determine if the
hardware actually completed the transfer. If QSPI_RDY is set, the
interrupt was legitimate and triggered by real hardware activity.
The fact that the timeout path handled it first doesn't make it
spurious. Returning IRQ_NONE incorrectly suggests the interrupt
wasn't for this device, which can cause issues with shared interrupt
lines and interrupt accounting.

Fixes: b4e002d8a7ce ("spi: tegra210-quad: Fix timeout handling")
Signed-off-by: Breno Leitao <leitao@debian.org>
---
 drivers/spi/spi-tegra210-quad.c | 19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

diff --git a/drivers/spi/spi-tegra210-quad.c b/drivers/spi/spi-tegra210-quad.c
index cdc3cb7c01f9b..f0408c0b4b981 100644
--- a/drivers/spi/spi-tegra210-quad.c
+++ b/drivers/spi/spi-tegra210-quad.c
@@ -1552,15 +1552,30 @@ static irqreturn_t handle_dma_based_xfer(struct tegra_qspi *tqspi)
 static irqreturn_t tegra_qspi_isr_thread(int irq, void *context_data)
 {
 	struct tegra_qspi *tqspi = context_data;
+	u32 status;
+
+	/*
+	 * Read transfer status to check if interrupt was triggered by transfer
+	 * completion
+	 */
+	status = tegra_qspi_readl(tqspi, QSPI_TRANS_STATUS);
 
 	/*
 	 * Occasionally the IRQ thread takes a long time to wake up (usually
 	 * when the CPU that it's running on is excessively busy) and we have
 	 * already reached the timeout before and cleaned up the timed out
 	 * transfer. Avoid any processing in that case and bail out early.
+	 *
+	 * If no transfer is in progress, check if this was a real interrupt
+	 * that the timeout handler already processed, or a spurious one.
 	 */
-	if (!tqspi->curr_xfer)
-		return IRQ_NONE;
+	if (!tqspi->curr_xfer) {
+		/* Spurious interrupt - transfer not ready */
+		if (!(status & QSPI_RDY))
+			return IRQ_NONE;
+		/* Real interrupt, already handled by timeout path */
+		return IRQ_HANDLED;
+	}
 
 	tqspi->status_reg = tegra_qspi_readl(tqspi, QSPI_FIFO_STATUS);
 

-- 
2.47.3