Re: [PATCH v3 3/8] firmware: smccc: lfa: Add timeout and trigger watchdog

[Andre Przywara <andre.przywara@arm.com>]

Hi,

On 7/10/26 12:08, Nirmoy Das wrote:
> On Mon, 6 Jul 2026 15:44:43 +0200, Andre Przywara wrote:
> 
> Hi Andre,
> 
>> From: Vedashree Vidwans <vvidwans@nvidia.com>
>>
>> Enhance PRIME/ACTIVATION functions to touch watchdog and implement
>> timeout mechanism. This update ensures that any potential hangs are
>> detected promptly and that the LFA process is allocated sufficient
>> execution time before the watchdog timer expires. These changes improve
>> overall system reliability by reducing the risk of undetected process
>> stalls and unexpected watchdog resets.
>>
>> Signed-off-by: Vedashree Vidwans <vvidwans@nvidia.com>
>> Signed-off-by: Andre Przywara <andre.przywara@arm.com>
>> ---
>>   drivers/firmware/smccc/lfa_fw.c | 43 ++++++++++++++++++++++++++++++---
>>   1 file changed, 39 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/firmware/smccc/lfa_fw.c b/drivers/firmware/smccc/lfa_fw.c
>> index b333b1e28c0d..357e41f95206 100644
>> --- a/drivers/firmware/smccc/lfa_fw.c
>> +++ b/drivers/firmware/smccc/lfa_fw.c
>> @@ -6,11 +6,14 @@
>>   #include <linux/arm-smccc.h>
>>   #include <linux/arm-smccc-bus.h>
>>   #include <linux/array_size.h>
>> +#include <linux/delay.h>
>>   #include <linux/fs.h>
>>   #include <linux/init.h>
>>   #include <linux/kobject.h>
>> +#include <linux/ktime.h>
>>   #include <linux/list.h>
>>   #include <linux/module.h>
>> +#include <linux/nmi.h>
>>   #include <linux/psci.h>
>>   #include <linux/stop_machine.h>
>>   #include <linux/string.h>
>> @@ -27,6 +30,11 @@
>>   #define LFA_PRIME_CALL_AGAIN		BIT(0)
>>   #define LFA_ACTIVATE_CALL_AGAIN		BIT(0)
>>   
>> +#define LFA_PRIME_BUDGET_MS		30000		/* 30s cap */
>> +#define LFA_PRIME_DELAY_MS		10		/* 10ms between polls */
>> +#define LFA_ACTIVATE_BUDGET_MS		10000		/* 10s cap */
>> +#define LFA_ACTIVATE_DELAY_MS		10		/* 10ms between polls */
>> +
>>   /* LFA return values */
>>   #define LFA_SUCCESS			0
>>   #define LFA_NOT_SUPPORTED		1
>> @@ -276,6 +284,7 @@ static int call_lfa_activate(void *data)
>>   	struct fw_image *image = data;
>>   	struct arm_smccc_1_2_regs reg = { 0 }, res;
>>   
>> +	touch_nmi_watchdog();
>>   	reg.a0 = ARM_SMCCC_LFA_ACTIVATE;
>>   	reg.a1 = image->fw_seq_id;
>>   	/*
>> @@ -299,6 +308,7 @@ static int call_lfa_activate(void *data)
>>   
>>   static int activate_fw_image(struct fw_image *image)
>>   {
>> +	ktime_t end = ktime_add_ms(ktime_get(), LFA_ACTIVATE_BUDGET_MS);
>>   	int ret;
>>   
>>   retry:
>> @@ -314,8 +324,14 @@ static int activate_fw_image(struct fw_image *image)
>>   	}
>>   
>>   	/* SMC returned with call_again flag set, or with LFA_BUSY */
>> -	if (ret == -LFA_CALL_AGAIN || ret == -LFA_BUSY)
>> -		goto retry;
>> +	if (ret == -LFA_CALL_AGAIN || ret == -LFA_BUSY) {
>> +		if (ktime_before(ktime_get(), end)) {
>> +			msleep_interruptible(LFA_ACTIVATE_DELAY_MS);
>> +			goto retry;
>> +		}
>> +
>> +		ret = -LFA_TIMED_OUT;
>> +	}
> 
> msleep_interruptible()'s return is ignored (here and in the PRIME
> loop), so a pending signal can turn this into premature retries.

Ah, thanks, that's a good point. I fixed that now. I don't think it 
really matters for the 10ms delay here, but it would break the outer 
timeout as well, which is a couple of seconds.

Cheers,
Andre

>>   
>>   	lfa_cancel(image);
>>   
>> @@ -328,6 +344,7 @@ static int activate_fw_image(struct fw_image *image)
>>   static int prime_fw_image(struct fw_image *image)
>>   {
>>   	struct arm_smccc_1_2_regs reg = { 0 }, res;
>> +	ktime_t end = ktime_add_ms(ktime_get(), LFA_PRIME_BUDGET_MS);
>>   
>>   	if (image->may_reset_cpu) {
>>   		pr_err("CPU reset not supported by kernel driver\n");
>> @@ -335,6 +352,8 @@ static int prime_fw_image(struct fw_image *image)
>>   		return -EINVAL;
>>   	}
>>   
>> +	touch_nmi_watchdog();
>> +
>>   	reg.a0 = ARM_SMCCC_LFA_PRIME;
>>   retry:
>>   	/*
>> @@ -353,8 +372,24 @@ static int prime_fw_image(struct fw_image *image)
>>   		return res.a0;
>>   	}
>>   
>> -	if (res.a1 & LFA_PRIME_CALL_AGAIN)
>> -		goto retry;
>> +	if (res.a1 & LFA_PRIME_CALL_AGAIN) {
>> +		int ret;
>> +
>> +		/* SMC returned with call_again flag set */
>> +		if (ktime_before(ktime_get(), end)) {
>> +			msleep_interruptible(LFA_PRIME_DELAY_MS);
>> +			goto retry;
>> +		}
>> +
>> +		pr_err("LFA_PRIME for image %s timed out",
>> +		       get_image_name(image));
>> +
>> +		ret = lfa_cancel(image);
>> +		if (ret != 0)
>> +			return ret;
>> +
>> +		return -ETIMEDOUT;
>> +	}
>>   
>>   	return 0;
>>   }
>> -- 
>> 2.43.0
> 
> Regards,
> Nirmoy