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

[PATCH] 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.

Also add a ratelimited warning when the outer limit expires, to aid in
debugging hardware stalls.

Fixes: c770d8631e18 ("spi: Add HiSilicon SPI Controller Driver for Kunpeng SoCs")
Signed-off-by: Pei Xiao <xiaopei01@kylinos.cn>
---
 drivers/spi/spi-hisi-kunpeng.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/drivers/spi/spi-hisi-kunpeng.c b/drivers/spi/spi-hisi-kunpeng.c
index 216a0a91fc47..b3359ac3a366 100644
--- a/drivers/spi/spi-hisi-kunpeng.c
+++ b/drivers/spi/spi-hisi-kunpeng.c
@@ -196,9 +196,22 @@ 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--);
+
+	if (!limit)
+		dev_warn_ratelimited(hs->dev, "SPI busy timeout\n");
 }
 
 /* Disable the controller and all interrupts */
-- 
2.25.1

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

[Mark Brown]

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On Wed, Mar 18, 2026 at 04:02:43PM +0800, Pei Xiao wrote:

> Also add a ratelimited warning when the outer limit expires, to aid in
> debugging hardware stalls.

That's a bit of a separate change, should really have been a separate
patch...

>  	} while (hisi_spi_busy(hs) && limit--);
> +
> +	if (!limit)
> +		dev_warn_ratelimited(hs->dev, "SPI busy timeout\n");
>  }

The limit check is a postdecrement so we read the value, compare it to
0, subtract 1 and then break out of the loop - that means that when we
come out of the loop the value of limit is non-zero again and the
warning won't trigger.

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

[Pei Xiao]

在 2026/3/18 21:17, Mark Brown 写道:
> On Wed, Mar 18, 2026 at 04:02:43PM +0800, Pei Xiao wrote:
>
>> Also add a ratelimited warning when the outer limit expires, to aid in
>> debugging hardware stalls.
> That's a bit of a separate change, should really have been a separate
> patch...
ok.
>>  	} while (hisi_spi_busy(hs) && limit--);
>> +
>> +	if (!limit)
>> +		dev_warn_ratelimited(hs->dev, "SPI busy timeout\n");
>>  }
> The limit check is a postdecrement so we read the value, compare it to
> 0, subtract 1 and then break out of the loop - that means that when we
> come out of the loop the value of limit is non-zero again and the
> warning won't trigger.

yes, my fault! I will use   '--limit'.

Thanks for your review and response!

Pei.

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

[Dan Carpenter]

Hi Pei,

kernel test robot noticed the following build warnings:

https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Pei-Xiao/spi-hisi-kunpeng-prevent-infinite-while-loop-in-hisi_spi_flush_fifo/20260318-211321
base:   https://git.kernel.org/pub/scm/linux/kernel/git/broonie/spi.git for-next
patch link:    https://lore.kernel.org/r/d50f1f46b2ee2bba05de9e2d4199353b545194e3.1773820898.git.xiaopei01%40kylinos.cn
patch subject: [PATCH] spi: hisi-kunpeng: prevent infinite while() loop in hisi_spi_flush_fifo
config: s390-randconfig-r072-20260319 (https://download.01.org/0day-ci/archive/20260319/202603192159.S0PIjhlg-lkp@intel.com/config)
compiler: clang version 23.0.0git (https://github.com/llvm/llvm-project 4abb927bacf37f18f6359a41639a6d1b3bffffb5)
smatch: v0.5.0-9004-gb810ac53

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
| Closes: https://lore.kernel.org/r/202603192159.S0PIjhlg-lkp@intel.com/

smatch warnings:
drivers/spi/spi-hisi-kunpeng.c:206 hisi_spi_flush_fifo() warn: should this be 'inner_limit == -1'

vim +206 drivers/spi/spi-hisi-kunpeng.c

c770d8631e1810 Jay Fang 2021-03-27  193  
c770d8631e1810 Jay Fang 2021-03-27  194  static void hisi_spi_flush_fifo(struct hisi_spi *hs)
c770d8631e1810 Jay Fang 2021-03-27  195  {
c770d8631e1810 Jay Fang 2021-03-27  196  	unsigned long limit = loops_per_jiffy << 1;
c770d8631e1810 Jay Fang 2021-03-27  197  
c770d8631e1810 Jay Fang 2021-03-27  198  	do {
e8821f559fed86 Pei Xiao 2026-03-18  199  		unsigned long inner_limit = loops_per_jiffy;
e8821f559fed86 Pei Xiao 2026-03-18  200  
e8821f559fed86 Pei Xiao 2026-03-18  201  		while (hisi_spi_rx_not_empty(hs) && inner_limit--) {
c770d8631e1810 Jay Fang 2021-03-27  202  			readl(hs->regs + HISI_SPI_DOUT);
e8821f559fed86 Pei Xiao 2026-03-18  203  			cpu_relax();
e8821f559fed86 Pei Xiao 2026-03-18  204  		}
e8821f559fed86 Pei Xiao 2026-03-18  205  
e8821f559fed86 Pei Xiao 2026-03-18 @206  		if (!inner_limit) {

This test is wrong.  Maybe change inner_limit-- to
--inner_limit.

e8821f559fed86 Pei Xiao 2026-03-18  207  			dev_warn_ratelimited(hs->dev, "RX FIFO flush timeout\n");
e8821f559fed86 Pei Xiao 2026-03-18  208  			break;
e8821f559fed86 Pei Xiao 2026-03-18  209  		}
e8821f559fed86 Pei Xiao 2026-03-18  210  
c770d8631e1810 Jay Fang 2021-03-27  211  	} while (hisi_spi_busy(hs) && limit--);
e8821f559fed86 Pei Xiao 2026-03-18  212  
e8821f559fed86 Pei Xiao 2026-03-18  213  	if (!limit)
e8821f559fed86 Pei Xiao 2026-03-18  214  		dev_warn_ratelimited(hs->dev, "SPI busy timeout\n");
c770d8631e1810 Jay Fang 2021-03-27  215  }

-- 
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https://github.com/intel/lkp-tests/wiki