linux-kernel - Re: [PATCH 17/17] arm64: Do not expose PCI mmap through procfs

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Message-ID: <517f4cc1-df3b-553b-59bf-f60ddd7c32d8@codeaurora.org>
Date:   Wed, 22 Mar 2017 11:40:52 -0400
From:   Sinan Kaya <okaya@...eaurora.org>
To:     Will Deacon <will.deacon@....com>
Cc:     David Woodhouse <dwmw2@...radead.org>, linux-pci@...r.kernel.org,
        linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 17/17] arm64: Do not expose PCI mmap through procfs

On 3/22/2017 10:18 AM, Will Deacon wrote:
> On Wed, Mar 22, 2017 at 10:15:04AM -0400, Sinan Kaya wrote:
>> On 3/22/2017 10:04 AM, David Woodhouse wrote:
>>> On Wed, 2017-03-22 at 09:54 -0400, Sinan Kaya wrote:
>>>> On 3/22/2017 9:25 AM, David Woodhouse wrote:
>>>>>
>>>>>  
>>>>> +#ifdef __aarch64__
>>>>> +/* ARM64 wants to be special and not expose this through /proc
>>>>> like everyone else */
>>>>> +#undef HAVE_PCI_MMAP
>>>>> +#endif
>>>>> +
>>>> Where is this ARM64 special requirement coming from?
>>>
>>> The idea is that as a new platform, ARM64 shouldn't need to implement
>>> legacy userspace interfaces.
>>>
>>> http://lists.infradead.org/pipermail/linux-arm-kernel/2016-April/422571.html
>>>
>>
>> Aren't we breaking an ABI for userspace? I know DPDK relies on this feature.
> 
> It relies on the /proc interface? That's the first I've ever heard of that
> -- everybody so far has only been interested in the sysfs stuff.
> 
> Nothing's more broken than before, because we've never supported the /proc
> interface, but if existing arm64 code out there is failing because of that
> then I'm of course open to supporting it. I'm just surprised that nobody
> else has come up with that before, since DPDK is in common use.
> 
> Can you point me at the specific code, please?

I'm correcting myself. I had to go back my memory from last year. 

DPDK requires HAVE_PCI_MMAP to be set. We have been carrying
some old maillist patch around for DPDK customers internally.

When HAVE_PCI_MMAP is set, resource files are created in sysfs and procfs.
DPDK is using the files in sysfs directory not procfs directory. 

Having HAVE_PCI_MMAP defined is the DPDK requirement.

> 
> Will
> 


-- 
Sinan Kaya
Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.