Re: [dpdk-dev] [EXT] Re: [PATCH v5 1/3] net/thunderx: enable build only on 64-bit Linux

[Ferruh Yigit <ferruh.yigit@intel.com>]

On 10/10/2021 10:38 AM, Jerin Jacob wrote:
> On Fri, Oct 8, 2021 at 9:00 PM Ferruh Yigit <ferruh.yigit@intel.com> wrote:
>>
>> On 10/4/2021 1:54 PM, Pavan Nikhilesh Bhagavatula wrote:
>>>> On 10/4/2021 1:01 PM, Pavan Nikhilesh Bhagavatula wrote:
>>>>>> On 10/4/2021 12:34 PM, Pavan Nikhilesh Bhagavatula wrote:
>>>>>>>> On 10/4/2021 11:02 AM, Pavan Nikhilesh Bhagavatula wrote:
>>>>>>>>>> On 10/4/2021 6:56 AM, pbhagavatula@marvell.com wrote:
>>>>>>>>>>> From: Pavan Nikhilesh <pbhagavatula@marvell.com>
>>>>>>>>>>>
>>>>>>>>>>> Due to Linux kernel AF(Admin function) driver dependency,
>>>> only
>>>>>>>>>> enable
>>>>>>>>>>> build for 64-bit Linux.
>>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> Hi Pavan,
>>>>>>>>>>
>>>>>>>>>> Isn't it possible to provide a commit log in the kernel side etc,
>>>> that
>>>>>> let
>>>>>>>>>> others to verify why only 64 bit is required, or if someone want
>>>> to
>>>>>>>>>> support
>>>>>>>>>> 32bit that may help them to investigate the source of the
>>>>>> restriction.
>>>>>>>>>
>>>>>>>>> Arch 32 support is not implemented on ThunderX, so 32bit will
>>>> not
>>>>>>>> run.
>>>>>>>>>
>>>>>>>>
>>>>>>>> I see, is following correct:
>>>>>>>> All thunderx, octeonx & octeontx2 only supports VF in the DPDK,
>>>>>> and PF
>>>>>>>> is
>>>>>>>> supported by Linux kernel driver. And Linux kernel driver doesn't
>>>>>>>> support arch32.
>>>>>>>
>>>>>>> AF != PF, AF is something that manages all the shared resources
>>>>>> between PF/VF.
>>>>>>>
>>>>>>
>>>>>> I see, I though AF is part of PF functionality. Are there two different
>>>>>> kernel
>>>>>> modules for PF and AF?
>>>>>>
>>>>>> So can DPDK driver drive PF? In a way, PF by DPDK, VF by DPDK, AF
>>>> by
>>>>>> Linux
>>>>>> kernel driver.
>>>>>
>>>>> Yup that’s correct.
>>>>>
>>>>>>
>>>>>>>>
>>>>>>>> Is something changed in kernel driver side to drop the 32bit
>>>> support?
>>>>>>>> If it was not supported at all, what is the motivation to disable the
>>>>>> DPDK
>>>>>>>> drivers now?
>>>>>>>>
>>>>>>>
>>>>>>> It was never supported to begin with, motivation is that build will
>>>> fail if
>>>>>> we try to
>>>>>>> compile with 32b.
>>>>>>>
>>>>>>
>>>>>> If there is no plan to support 32bit in the kernel side, that is
>>>> reasonable
>>>>>> to
>>>>>> disable 32bit build, please provide above details in the commit log.
>>>>>>
>>>>>> And after above said, how much maintenance cost to support 32bit,
>>>> if
>>>>>> the build
>>>>>> error is on the logging format "%lx" etc .. (as we mostly have 32bit
>>>> build
>>>>>> errors), it is better to fix them using 'PRIx64' which is more proper
>>>> way
>>>>>> anyway. If there is more logical issue with 32bit pointers, I agree with
>>>>>> you to
>>>>>> disable it.
>>>>>> Can you please provided the build error in the commit log as record?
>>>>>>
>>>>>
>>>>> Apologies, I meant that all the functions that don’t fall under 64b are
>>>> stubbed out
>>>>> so the driver wouldn’t work.
>>>>>
>>>>
>>>> so is there build error or not?
>>>>
>>>
>>> No build error.
>>>
>>
>> Just trying to clarify,
>>
>> Linux kernel AF kernel driver only build for 64-bit Linux.
>> And mentioned DPDK drivers have a dependency to this kernel module.
>>
>> But DPDK drivers are userspace application, can't 32-bit application
>> run on 64-bit Linux?
>>
>> Can you please clarify what exactly is not supported?
> 
> 
> armv8 specification has two operating modes,
> 
> 1) AArch32 mode, where a 32 bit application can run on armv8
> 2) AArch64 mode, where it is native 64bit support.
> 
> In Thunderx and Octeon families, AArch32 mode is not implemented to save
> the power and RTL cost. So it can never use AArch32 32bit mode.
> 
> There was an attempt to emulate 32bit mode in 64 bit like X32_ABI, it
> is called IPL32 in arm64, that never became mainstream. So 32bit application
> can not run on ThunderX/Octeontx so we would like to remove building this option
> to avoid removing the cost of maintaining it.
> 
> 

Thanks for the clarification, so main motivation is not the AF driver dependency?

Can you please put above description to the commit log in next version?

Thanks,
ferruh

> 
>>
>>
>>>>>>>>>>
>>>>>>>>>>> Signed-off-by: Pavan Nikhilesh <pbhagavatula@marvell.com>
>>>>>>>>>>> Acked-by: Jerin Jacob <jerinj@marvell.com>
>>>>>>>>>>> ---
>>>>>>>>>>>    v5 Changes
>>>>>>>>>>>    - s/fuction/function.
>>>>>>>>>>>
>>>>>>>>>>>    v4 Changes:
>>>>>>>>>>>    - Update commit message regarding dependency on AF
>>>> driver.
>>>>>>>>>>>
>>>>>>>>>>>    drivers/net/thunderx/meson.build | 4 ++--
>>>>>>>>>>>    1 file changed, 2 insertions(+), 2 deletions(-)
>>>>>>>>>>>
>>>>>>>>>>> diff --git a/drivers/net/thunderx/meson.build
>>>>>>>>>> b/drivers/net/thunderx/meson.build
>>>>>>>>>>> index 4bbcea7f93..da665bd76f 100644
>>>>>>>>>>> --- a/drivers/net/thunderx/meson.build
>>>>>>>>>>> +++ b/drivers/net/thunderx/meson.build
>>>>>>>>>>> @@ -1,9 +1,9 @@
>>>>>>>>>>>    # SPDX-License-Identifier: BSD-3-Clause
>>>>>>>>>>>    # Copyright(c) 2017 Cavium, Inc
>>>>>>>>>>>
>>>>>>>>>>> -if is_windows
>>>>>>>>>>> +if not is_linux or not dpdk_conf.get('RTE_ARCH_64')
>>>>>>>>>>>        build = false
>>>>>>>>>>> -    reason = 'not supported on Windows'
>>>>>>>>>>> +    reason = 'only supported on 64-bit Linux'
>>>>>>>>>>>        subdir_done()
>>>>>>>>>>>    endif
>>>>>>>>>>>
>>>>>>>>>>> --
>>>>>>>>>>> 2.17.1
>>>>>>>>>>>
>>>>>>>>>
>>>>>>>
>>>>>
>>>
>>