[PATCH 5.4.y] spi: cadence-quadspi: Flush posted register writes before INDAC access

[Sasha Levin <sashal@kernel.org>]

From: Pratyush Yadav <pratyush@kernel.org>

[ Upstream commit 29e0b471ccbd674d20d4bbddea1a51e7105212c5 ]

cqspi_indirect_read_execute() and cqspi_indirect_write_execute() first
set the enable bit on APB region and then start reading/writing to the
AHB region. On TI K3 SoCs these regions lie on different endpoints. This
means that the order of the two operations is not guaranteed, and they
might be reordered at the interconnect level.

It is possible for the AHB write to be executed before the APB write to
enable the indirect controller, causing the transaction to be invalid
and the write erroring out. Read back the APB region write before
accessing the AHB region to make sure the write got flushed and the race
condition is eliminated.

Fixes: 140623410536 ("mtd: spi-nor: Add driver for Cadence Quad SPI Flash Controller")
CC: stable@vger.kernel.org
Reviewed-by: Pratyush Yadav <pratyush@kernel.org>
Signed-off-by: Pratyush Yadav <pratyush@kernel.org>
Signed-off-by: Santhosh Kumar K <s-k6@ti.com>
Message-ID: <20250905185958.3575037-2-s-k6@ti.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
[ applied changes to drivers/mtd/spi-nor/cadence-quadspi.c instead of drivers/spi/spi-cadence-quadspi.c ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/mtd/spi-nor/cadence-quadspi.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/mtd/spi-nor/cadence-quadspi.c b/drivers/mtd/spi-nor/cadence-quadspi.c
index 7bdc558d85601..2d6f008adb073 100644
--- a/drivers/mtd/spi-nor/cadence-quadspi.c
+++ b/drivers/mtd/spi-nor/cadence-quadspi.c
@@ -523,6 +523,7 @@ static int cqspi_indirect_read_execute(struct spi_nor *nor, u8 *rxbuf,
 	reinit_completion(&cqspi->transfer_complete);
 	writel(CQSPI_REG_INDIRECTRD_START_MASK,
 	       reg_base + CQSPI_REG_INDIRECTRD);
+	readl(reg_base + CQSPI_REG_INDIRECTRD); /* Flush posted write. */
 
 	while (remaining > 0) {
 		if (!wait_for_completion_timeout(&cqspi->transfer_complete,
@@ -633,6 +634,8 @@ static int cqspi_indirect_write_execute(struct spi_nor *nor, loff_t to_addr,
 	reinit_completion(&cqspi->transfer_complete);
 	writel(CQSPI_REG_INDIRECTWR_START_MASK,
 	       reg_base + CQSPI_REG_INDIRECTWR);
+	readl(reg_base + CQSPI_REG_INDIRECTWR); /* Flush posted write. */
+
 	/*
 	 * As per 66AK2G02 TRM SPRUHY8F section 11.15.5.3 Indirect Access
 	 * Controller programming sequence, couple of cycles of
-- 
2.51.0