linux-kernel - Re: [PATCH v2 11/13] NTB: convert to dmaengine_unmap

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Message-ID: <CAA9_cmd08gFK3a5MwK8Ftxn9Ta9A=_vxvug8CPHh-HDUbPYETw@mail.gmail.com>
Date:	Tue, 22 Oct 2013 18:05:31 -0700
From:	Dan Williams <dan.j.williams@...el.com>
To:	Jon Mason <jon.mason@...el.com>
Cc:	dmaengine@...r.kernel.org, Dave Jiang <dave.jiang@...el.com>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
	Vinod Koul <vinod.koul@...el.com>,
	Tomasz Figa <t.figa@...sung.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Kyungmin Park <kyungmin.park@...sung.com>,
	Russell King - ARM Linux <linux@....linux.org.uk>
Subject: Re: [PATCH v2 11/13] NTB: convert to dmaengine_unmap_data

On Tue, Oct 22, 2013 at 4:12 PM, Jon Mason <jon.mason@...el.com> wrote:
> On Tue, Oct 22, 2013 at 02:29:36PM -0700, Dan Williams wrote:
>> On Fri, Oct 18, 2013 at 6:06 PM, Jon Mason <jon.mason@...el.com> wrote:
>> > On Fri, Oct 18, 2013 at 07:35:31PM +0200, Bartlomiej Zolnierkiewicz wrote:
>> >> Use the generic unmap object to unmap dma buffers.
>> >>
>> >> As NTB can be compiled without DMA_ENGINE support add
>> >
>> > Seems like the stubs should be added outside of this patch.
>>
>> I think they are ok here as this is the only driver that uses them.
>> The alternative is a new api patch without a user.
>>
>> > Also, the
>> > comment implies that NTB could not be compiled without DMA_ENGINE
>> > support before, which it could be.
>>
>> Hmm, I read it as "since NTB *can* be compiled without dmaengine here
>> are some stubs".
>
> This poses an overall question of whether it would simply be better to
> abstract all of the with/without DMA_ENGINE part and simply remap it
> to memcpy if DMA_ENGINE is not set (or if the DMA engine is
> hotplugged).  Of course, this is outside the scope of this patch.

That's at least the promise of async_memcpy() it does not care if a
channel is there or not, but I think it is better if the client has a
strict dma and non-dma path.  Hiding the dma details from the client
seems to have been the wrong choice at least for raid.

> That is fine.  It can be like this in the short term.
>
> Thanks,
> Jon

I'll take that as:

Acked-by: Jon Mason <jon.mason@...el.com>

...but holler if not.
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