On 21/03/2021 22:09, Arnd Bergmann wrote:
> On Sun, Mar 21, 2021 at 7:46 PM Krzysztof Kozlowski
> <krzysztof.kozlow...@canonical.com> wrote:
>>
>> The Stratix10 service layer and RCU drivers are useful only on
>> Stratix10, so on ARMv8. Compile testing the RCU driver on 32-bit ARM
>> fails:
>>
>> drivers/firmware/stratix10-rsu.c: In function 'rsu_status_callback':
>> include/linux/compiler_types.h:320:38: error: call to
>> '__compiletime_assert_179'
>> declared with attribute error: FIELD_GET: type of reg too small for mask
>> _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
>> ...
>> drivers/firmware/stratix10-rsu.c:96:26: note: in expansion of macro
>> 'FIELD_GET'
>> priv->status.version = FIELD_GET(RSU_VERSION_MASK,
>>
>> Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlow...@canonical.com>
>> Reported-by: kernel test robot <l...@intel.com>
>
> While I agree that one shouldn't run 32-bit kernels on this, we should also
> try
> to write drivers portably, and in theory any SoC that can run a 64-bit
> Arm kernel
> should also be able to run a 32-bit kernel if you include the same drivers.
>
> It seems that the problem here is in the smccc definition
>
> struct arm_smccc_res {
> unsigned long a0;
> unsigned long a1;
> unsigned long a2;
> unsigned long a3;
> };
>
> so the result of
>
> #define RSU_VERSION_MASK GENMASK_ULL(63, 32)
> priv->status.version = FIELD_GET(RSU_VERSION_MASK, res->a2);
>
> tries to access bits that are just not returned by the firmware here,
> which indicates that it probably won't work in this case.
>
> What I'm not entirely sure about is whether this is a problem in
> the Intel firmware implementation requiring the smccc caller to
> run in a 64-bit context, or if it's a mistake in the way the driver
> extracts the information if the firmware can actually pass it down
> correctly.
The SMC has two calling conventions - SMC32/HVC32 and SMC64/HVC64. The
Stratix 10 driver uses the 64-bit calling convention (see
INTEL_SIP_SMC_FAST_CALL_VAL in
include/linux/firmware/intel/stratix10-smc.h), so it should not run in
aarch32 (regardless of type of hardware).
I think that my patch limiting the support to 64-bit makes sense.
Best regards,
Krzysztof
