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

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Date:   Mon, 22 Mar 2021 07:58:19 -0500
From:   Richard Gong <richard.gong@...ux.intel.com>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>,
        Arnd Bergmann <arnd@...db.de>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Dinh Nguyen <dinguyen@...nel.org>, kbuild-all@...ts.01.org,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        kernel test robot <lkp@...el.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Jens Wiklander <jens.wiklander@...aro.org>
Subject: Re: [PATCH] firmware: stratix10-svc: build only on 64-bit ARM



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@...onical.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.kozlowski@...onical.com>
>>> Reported-by: kernel test robot <lkp@...el.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.
> 

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

> Best regards,
> Krzysztof
>