[PATCH 1/2] spi: hisi-kunpeng: prevent infinite while() loop in hisi_spi_flush_fifo

[Pei Xiao]

The hisi_spi_flush_fifo()'s inner while loop that lacks any timeout
mechanism. Maybe the hardware never becomes empty, the loop will spin
forever, causing the CPU to hang.

Fix this by adding a inner_limit based on loops_per_jiffy. The inner loop
now exits after approximately one jiffy if the FIFO remains non-empty, logs
a ratelimited warning, and breaks out of the outer loop. Additionally, add
a cpu_relax() inside the busy loop to improve power efficiency.

Fixes: c770d8631e18 ("spi: Add HiSilicon SPI Controller Driver for Kunpeng SoCs")
Signed-off-by: Pei Xiao <xiaopei01@xxxxxxxxxx>
---
 drivers/spi/spi-hisi-kunpeng.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/drivers/spi/spi-hisi-kunpeng.c b/drivers/spi/spi-hisi-kunpeng.c
index 216a0a91fc47..c42d2a2cdf1e 100644
--- a/drivers/spi/spi-hisi-kunpeng.c
+++ b/drivers/spi/spi-hisi-kunpeng.c
@@ -196,8 +196,18 @@ static void hisi_spi_flush_fifo(struct hisi_spi *hs)
 	unsigned long limit = loops_per_jiffy << 1;
 
 	do {
-		while (hisi_spi_rx_not_empty(hs))
+		unsigned long inner_limit = loops_per_jiffy;
+
+		while (hisi_spi_rx_not_empty(hs) && --inner_limit) {
 			readl(hs->regs + HISI_SPI_DOUT);
+			cpu_relax();
+		}
+
+		if (!inner_limit) {
+			dev_warn_ratelimited(hs->dev, "RX FIFO flush timeout\n");
+			break;
+		}
+
 	} while (hisi_spi_busy(hs) && limit--);
 }
 
-- 
2.25.1