linux-kernel - Re: [PATCH v5 19/27] IB/Verbs: Use management helper cap_iw

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Date:	Mon, 20 Apr 2015 11:39:03 -0500
From:	Tom Tucker <tom@...ngridcomputing.com>
To:	Jason Gunthorpe <jgunthorpe@...idianresearch.com>
CC:	Michael Wang <yun.wang@...fitbricks.com>,
	Steve Wise <swise@...ngridcomputing.com>,
	Roland Dreier <roland@...nel.org>,
	Sean Hefty <sean.hefty@...el.com>, linux-rdma@...r.kernel.org,
	linux-kernel@...r.kernel.org, hal@....mellanox.co.il,
	Hoang-Nam Nguyen <hnguyen@...ibm.com>,
	Christoph Raisch <raisch@...ibm.com>,
	Mike Marciniszyn <infinipath@...el.com>,
	Eli Cohen <eli@...lanox.com>,
	Faisal Latif <faisal.latif@...el.com>,
	Jack Morgenstein <jackm@....mellanox.co.il>,
	Or Gerlitz <ogerlitz@...lanox.com>,
	Haggai Eran <haggaie@...lanox.com>,
	Ira Weiny <ira.weiny@...el.com>, Tom Talpey <tom@...pey.com>,
	Doug Ledford <dledford@...hat.com>
Subject: Re: [PATCH v5 19/27] IB/Verbs: Use management helper cap_iw_cm()

On 4/20/15 11:19 AM, Jason Gunthorpe wrote:
> On Mon, Apr 20, 2015 at 10:51:58AM -0500, Tom Tucker wrote:
>> On 4/20/15 10:16 AM, Michael Wang wrote:
>>> On 04/20/2015 04:00 PM, Steve Wise wrote:
>>>> On 4/20/2015 3:40 AM, Michael Wang wrote:
>>> [snip]
>>>>> diff --git a/include/rdma/ib_verbs.h b/include/rdma/ib_verbs.h
>>>>> index 6805e3e..e4999f6 100644
>>>>> +++ b/include/rdma/ib_verbs.h
>>>>> @@ -1818,6 +1818,21 @@ static inline int cap_ib_cm(struct ib_device *device, u8 port_num)
>>>>>        return rdma_ib_or_iboe(device, port_num);
>>>>>    }
>>>>>    +/**
>>>>> + * cap_iw_cm - Check if the port of device has the capability IWARP
>>>>> + * Communication Manager.
>>>>> + *
>>>>> + * @device: Device to be checked
>>>>> + * @port_num: Port number of the device
>>>>> + *
>>>>> + * Return 0 when port of the device don't support IWARP
>>>>> + * Communication Manager.
>>>>> + */
>>>>> +static inline int cap_iw_cm(struct ib_device *device, u8 port_num)
>>>>> +{
>>>>> +    return rdma_tech_iwarp(device, port_num);
>>>>> +}
>>>>> +
>>>>>    int ib_query_gid(struct ib_device *device,
>>>>>             u8 port_num, int index, union ib_gid *gid);
>>>> iWARP devices _must_ support the IWCM so cap_iw_cm() is not really useful.
>>> Sean suggested to add this helper paired with cap_ib_cm(), may be there are
>>> some consideration on maintainability?
>>>
>>> Me too also prefer this way to make the code more readable ;-)
>> It's more consistent, but not necessarily more readable -- if by
>> readability we mean understanding.
>>
>> If the reader knows how the transports work, then the reader would
>> be confused by the addition of a check that is always true. For the
>> reader that doesn't know, the addition of the check implies that the
>> support is optional, which it is not.
> No, it says this code is concerned with the unique parts of iWarp
> related to CM, not the other unique parts of iWarp. The check isn't
> aways true, it is just always true on iWarp devices.
>
> That became the problem with the old way of just saying 'is iWarp'
> (and others). There are too many differences, the why became lost in
> many places.
>
> There are now too many standards, and several do not have public docs,
> to keep relying on a mess of 'is standard' tests.

You're right Jason, this gets called with the device handle so it's only 
true for iwarp.

> Jason
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