linux-kernel - Re: [PATCH] dmaengine: dma40: Add support to split up large elements

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Message-ID: <AANLkTik94Go7W4AMquncm-novWkHtLOBRn7BfpepoEZz@mail.gmail.com>
Date:	Tue, 21 Dec 2010 20:28:21 +0100
From:	Linus Walleij <linus.ml.walleij@...il.com>
To:	Dan Williams <dan.j.williams@...el.com>
Cc:	Per Forlin <per.forlin@...ricsson.com>,
	linux-kernel@...r.kernel.org, Per Forlin <per.forlin@...aro.org>,
	Rabin VINCENT <rabin.vincent@...ricsson.com>
Subject: Re: [PATCH] dmaengine: dma40: Add support to split up large elements

2010/12/21 Dan Williams <dan.j.williams@...el.com>:

> If that is the case then the temporary fix for 2.6.37 is along the
> lines of fixing up the clients to not submit such large requests.

They don't, currently. We actually had some debate about this
internally, because the only driver submitting something >64K-1
was the MMCI driver (which is yet not in mainline) and yes, indeed
the suggested solution was to amend the MMCI driver
for the time being.

I insisted on doing this fix anyway because I was under the
impression that memcpy() is supposed to handle *any* size of
request, is this the intention?

Since its semantics are not documented as far as I can see I
was maybe misguided in assuming that any size of buffer should
be possible to pass in... :-(

>  You
> mention the "memcpy api contract" can this be triggered outside of
> dmatest?

Nope. That and out-of-tree MMCI.

So for the next merge window it is, if the patch is semantically
correct.

Yours,
Linus Walleij
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