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

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Message-ID: <5c4ede72-b937-586b-78d7-1f6770c23b09@canonical.com>
Date:   Mon, 22 Mar 2021 13:41:18 +0100
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>
To:     Richard Gong <richard.gong@...ux.intel.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 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?
2. Does the actual firmware support 32-bit SMC convention call?

Best regards,
Krzysztof