Re: [linux-next:master 8264/14724] drivers/firmware/smccc/smccc.c:141:1: error: r7 cannot be used in asm here

[Aneesh Kumar K.V <aneesh.kumar@kernel.org>]

Sudeep Holla <sudeep.holla@kernel.org> writes:

> (+ Marc, Mark)
>
> On Wed, Oct 07, 2026 at 12:28:54PM +0530, Aneesh Kumar K.V wrote:
>> kernel test robot <lkp@intel.com> writes:
>> 
>> > tree:   https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master
>> > head:   eea3fef32a9cf36abcb5975a5a594e4135a6b026
>> > commit: d8263a131bb05398faa72ac32be54a03e48fa197 [8264/14724] firmware: hwrng: arm_smccc_trng: Register as an SMCCC device
>> > config: arm-randconfig-1001-20261007 (https://download.01.org/0day-ci/archive/20261007/202610070641.B8hxBJcf-lkp@intel.com/config)
>> > compiler: arm-linux-gnueabi-gcc (GCC) 8.5.0
>> > reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20261007/202610070641.B8hxBJcf-lkp@intel.com/reproduce)
>> >
>> > 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>
>> > | Closes: https://lore.kernel.org/oe-kbuild-all/202610070641.B8hxBJcf-lkp@intel.com/
>> >
>> > All errors (new ones prefixed by >>):
>> >
>> >    drivers/firmware/smccc/smccc.c: In function 'smccc_devices_init':
>> >>> drivers/firmware/smccc/smccc.c:141:1: error: r7 cannot be used in asm here
>> >     }
>> >     ^
>> >>> drivers/firmware/smccc/smccc.c:141:1: error: r7 cannot be used in asm here
>> >
>> >
>> > vim +141 drivers/firmware/smccc/smccc.c
>> >
>> > d8263a131bb0539 Aneesh Kumar K.V (Arm  2026-09-23  122) 
>> > b83c2d92be719bf Andre Przywara         2021-07-31  123  static int __init smccc_devices_init(void)
>> > b83c2d92be719bf Andre Przywara         2021-07-31  124  {
>> > d8263a131bb0539 Aneesh Kumar K.V (Arm  2026-09-23  125) 	struct arm_smccc_device *sdev;
>> > d8263a131bb0539 Aneesh Kumar K.V (Arm  2026-09-23  126) 	const struct smccc_device_info *smccc_dev;
>> > d8263a131bb0539 Aneesh Kumar K.V (Arm  2026-09-23  127) 
>> > d8263a131bb0539 Aneesh Kumar K.V (Arm  2026-09-23  128) 	for (int i = 0; i < ARRAY_SIZE(smccc_devices); i++) {
>> > d8263a131bb0539 Aneesh Kumar K.V (Arm  2026-09-23  129) 		smccc_dev = &smccc_devices[i];
>> > d8263a131bb0539 Aneesh Kumar K.V (Arm  2026-09-23  130) 
>> > d8263a131bb0539 Aneesh Kumar K.V (Arm  2026-09-23  131) 		if (!smccc_probe_smccc_device(smccc_dev))
>> > d8263a131bb0539 Aneesh Kumar K.V (Arm  2026-09-23  132) 			continue;
>> > d8263a131bb0539 Aneesh Kumar K.V (Arm  2026-09-23  133) 
>> > d8263a131bb0539 Aneesh Kumar K.V (Arm  2026-09-23  134) 		sdev = arm_smccc_device_register(smccc_dev->device_name, smccc_dev->func_id);
>> > d8263a131bb0539 Aneesh Kumar K.V (Arm  2026-09-23  135) 		if (IS_ERR(sdev))
>> > d8263a131bb0539 Aneesh Kumar K.V (Arm  2026-09-23  136) 			pr_err("%s: could not register device: %pe\n",
>> > d8263a131bb0539 Aneesh Kumar K.V (Arm  2026-09-23  137) 			       smccc_dev->device_name, sdev);
>> > b83c2d92be719bf Andre Przywara         2021-07-31  138  	}
>> > b83c2d92be719bf Andre Przywara         2021-07-31  139  
>> > b83c2d92be719bf Andre Przywara         2021-07-31  140  	return 0;
>> > b83c2d92be719bf Andre Przywara         2021-07-31 @141  }
>> >
>> 
>> 
>> This is with:
>> 
>> CONFIG_ARM_THUMB=y
>> CONFIG_ARM_THUMBEE=y
>> 
>> where there are restrictions on the use of r7. IMHO, this needs to be
>> addressed in the implementation of arm_smccc_1_1_invoke(), rather than
>> worked around in this patch?
>>
>
> We can even drop the extra arguments set 0 as it was original used in
> TRNG or just use 4 arguments. That shouldn't impact <FEAT>_VERSION ABIs.
>
> I think there is a precedent here with `SMCCC_ARCH_WORKAROUND_*` calls.
> `__arm_smccc_1_1()` is deliberately variadic: it sets up only the input
> registers supplied by the caller. Not sure if it is trivial to meddle with
> the macro to handle this as workaround.
>
> Regards,
> Sudeep
>
> -->8
>
> diff --git i/drivers/firmware/smccc/smccc.c w/drivers/firmware/smccc/smccc.c
> index afc2e4d602ba..dfbd04c8eeac 100644
> --- i/drivers/firmware/smccc/smccc.c
> +++ w/drivers/firmware/smccc/smccc.c
> @@ -116,8 +116,7 @@ static bool __init smccc_probe_smccc_device(const struct smccc_device_info *smcc
>         if (IS_ENABLED(CONFIG_ARM) && ARM_SMCCC_IS_64(smccc_dev->func_id))
>                 return false;
>
> -       arm_smccc_1_1_invoke(smccc_dev->func_id,
> -                            0, 0, 0, 0, 0, 0, 0, &res);
> +       arm_smccc_1_1_invoke(smccc_dev->func_id, &res);
>         ret = res.a0;
>

However, we used the seven-argument form here because we do not know
which input registers a particular SMCCC function may use.

-aneesh