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

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Date:   Mon, 22 Mar 2021 10:29:10 -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 7:41 AM, Krzysztof Kozlowski wrote:
> On 22/03/2021 13:58, Richard Gong wrote:
>>
>>
>> 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.
> 
> This we know, however the questions were:
> 1. Why the driver cannot be made portable? Why it cannot be developed in
> a way it allows building on different platforms?

The drivers was originally developed for Intel Stratix10 SoCFPGA 
platform, which is ARM 64-bit architecture. The same drivers can be used 
for other Intel ARM 64-bit SoCFPGA platforms (Agilex, eASIC N5X as 
example), which have the same SDM architecture as Stratix10 has.

SDM = Secure Device Manager

So far Intel 32-bit SoCFPGA platform doesn't support SDM architecture.

> 2. Does the actual firmware support 32-bit SMC convention call?

No.

> 
> Best regards,
> Krzysztof
> 

Regards,
Richard