Re: [PATCH] firmware: stratix10-svc: build only on 64-bit ARM

[Richard Gong]

On 3/22/21 3:26 AM, Krzysztof Kozlowski wrote:
> On 21/03/2021 22:09, Arnd Bergmann wrote:
> > On Sun, Mar 21, 2021 at 7:46 PM Krzysztof Kozlowski
> > <krzysztof.kozlowski@xxxxxxxxxxxxx> 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.kozlowski@xxxxxxxxxxxxx>
> > > Reported-by: kernel test robot <lkp@xxxxxxxxx>
> >
> > 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.

The stratix10 service layer and RSU driver are only used in Intel 64-bit 
SoCFPGA platforms.

> Best regards,
> Krzysztof