From: Arnd Bergmann <arnd@arndb.de>
To: Vinod Koul <vinod.koul@intel.com>
Cc: Peter Ujfalusi <peter.ujfalusi@ti.com>,
        Geert Uytterhoeven <geert@linux-m68k.org>,
        Tony Lindgren <tony@atomide.com>,
        "devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Dan Williams <dan.j.williams@intel.com>, dmaengine@vger.kernel.org,
        "linux-serial@vger.kernel.org" <linux-serial@vger.kernel.org>,
        "linux-omap@vger.kernel.org" <linux-omap@vger.kernel.org>,
        Linux MMC List <linux-mmc@vger.kernel.org>,
        linux-crypto@vger.kernel.org, linux-spi <linux-spi@vger.kernel.org>,
        Linux Media Mailing List <linux-media@vger.kernel.org>,
        ALSA Development Mailing List <alsa-devel@alsa-project.org>
Subject: Re: [PATCH 02/13] dmaengine: Introduce dma_request_slave_channel_compat_reason()
Date: Thu, 25 Jun 2015 13:15:57 +0200
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On Wednesday 24 June 2015 21:54:01 Vinod Koul wrote:
> > It would be nice to find another name for the
> > dma_request_slave_channel_compat() so with the new name we could have chance
> > to rearrange the parameters: (dev, name, mask, fn, fn_param)
> > 
> > We would end up with the following APIs, all returning with error code on failure:
> > dma_request_slave_channel(dev, name);
> > dma_request_channel_legacy(mask, fn, fn_param);
> > dma_request_slave_channel_compat(mask, fn, fn_param, dev, name);
> > dma_request_any_channel(mask);
> This is good idea but still we end up with 4 APIs. Why not just converge to
> two API, one legacy + memcpy + filer fn and one untimate API for slave?
> 
> Internally we may have 4 APIs for cleaner handling...
> 

Not sure if it's realistic, but I think it would be nice to have
a way for converting the current slave drivers that use the
mask/filter/param API to the dev/name based API. We should
be able to do this by registering a lookup table from platform
code that translates one to the other, like we do with the
clkdev lookup to find a device clock based on a local identifier.

The main downside of this is that it's a lot of work if we want
to completely remove dma_request_channel() for slave drivers,
but it could be done more gradually.

Another upside is that we could come up with a mechanism to
avoid the link-time dependency on the filter-function that
causes problems when that filter is defined in a loadable
module for the dmaengine driver.

	Arnd
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