spi: hisi-kunpeng: prevent infinite while() loop in hisi_spi_flush_fifo

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@kylinos.cn>
Link: https://patch.msgid.link/d834ce28172886bfaeb9c8ca00cfd9bf1c65d5a1.1773889292.git.xiaopei01@kylinos.cn
Signed-off-by: Mark Brown <broonie@kernel.org>

diff --git a/drivers/spi/spi-hisi-kunpeng.c b/drivers/spi/spi-hisi-kunpeng.c
index 216a0a91fc47db9e1fbeb59559369a43768b54d3..c42d2a2cdf1e469570772a4ee4b939e08c556493 100644 (file)
--- 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--);
 }