linux-kernel - Re: Why move all map_sg/unmap_sg for slave channel to its client?

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Message-ID: <BANLkTik9kZjJs5H2kvM+xAtd_CR5NA0dDw@mail.gmail.com>
Date:	Thu, 9 Jun 2011 11:38:11 +0200
From:	Linus Walleij <linus.walleij@...aro.org>
To:	viresh kumar <viresh.kumar@...com>
Cc:	"Koul, Vinod" <vinod.koul@...el.com>,
	Dan Williams <dan.j.williams@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	anemo@....ocn.ne.jp, Shiraz HASHIM <shiraz.hashim@...com>,
	Armando VISCONTI <armando.visconti@...com>,
	Bhupesh SHARMA <bhupesh.sharma@...com>
Subject: Re: Why move all map_sg/unmap_sg for slave channel to its client?

On Thu, Jun 9, 2011 at 8:54 AM, viresh kumar <viresh.kumar@...com> wrote:

> I thought map_sg/unmap_sg for slave channels will be handled according
> to the flags passed in prep_slave_sg(). But then i found following patch:
> (...)
> I don't have much knowledge about that discussion, but i think this should be left
> configurable.
> If the client wants to control map/unmap then it can simply pass
> DMA_COMPL_SKIP_DEST_UNMAP | DMA_COMPL_SKIP_SRC_UNMAP in flags. I didn't wanted to
> skip this in my driver and so i don't pass them.

What if the same driver is used on many different platforms like say
drivers/tty/serial/amba-pl011.c, and some of the platforms using it
has DMA engines that does not implement mapping/unmapping of
the passed sglist?

In that case I think you have to modify all drivers in drivers/dma/*
to do this mapping, and then you could just make it a required behaviour
and skip the flags altogether.

But apparently that approach was blocked at one point so let's see
what the others say.

Yours,
Linus Walleij
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