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Message-Id: <201306242228.23297.arnd@arndb.de>
Date:	Mon, 24 Jun 2013 22:28:23 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Joel A Fernandes <agnel.joel@...il.com>
Cc:	Sekhar Nori <nsekhar@...com>, Joel A Fernandes <joelagnel@...com>,
	Tony Lindgren <tony@...mide.com>,
	Matt Porter <matt@...orter.com>,
	Grant Likely <grant.likely@...retlab.ca>,
	Rob Herring <rob.herring@...xeda.com>,
	Vinod Koul <vinod.koul@...el.com>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Benoit Cousson <b-cousson@...com>,
	Russell King <linux@....linux.org.uk>,
	Rob Landley <rob@...dley.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jason Kridner <jkridner@...gleboard.org>,
	Koen Kooi <koen@...gleboard.org>,
	Devicetree Discuss <devicetree-discuss@...ts.ozlabs.org>,
	Linux OMAP List <linux-omap@...r.kernel.org>,
	Linux ARM Kernel List <linux-arm-kernel@...ts.infradead.org>,
	Linux DaVinci Kernel List 
	<davinci-linux-open-source@...ux.davincidsp.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linux Documentation List <linux-doc@...r.kernel.org>,
	Linux MMC List <linux-mmc@...r.kernel.org>,
	Linux SPI Devel List 
	<spi-devel-general@...ts.sourceforge.net>
Subject: Re: [PATCH v12 05/11] edma: config: Enable config options for EDMA

On Saturday 22 June 2013, Joel A Fernandes wrote:
> 
> >> > config TI_EDMA
> >> >         tristate "TI EDMA support"
> >> >         default m if 'ARCH_DAVINCI || ARCH_OMAP1 || ARCH_OMAP2
> >> >         select DMA_ENGINE
> >> >         select DMA_VIRTUAL_CHANNELS
> >>
> >>
> >> MMC depends on EDMA specially on AM33xx there's no PIO mode AFAIK. The
> >> 'm' option will require some initramfs to load the module when needing
> >> to MMC boot, I suggest lets leave it as y.
> >>
> >
> > Ah, right: you still export a filter function from the edma driver
> > and use it in slave drivers:
> >
> > drivers/mmc/host/davinci_mmc.c:         dma_request_slave_channel_compat(mask, edma_filter_fn,
> > drivers/mmc/host/davinci_mmc.c:         dma_request_slave_channel_compat(mask, edma_filter_fn,
> > drivers/spi/spi-davinci.c:      dspi->dma_rx = dma_request_channel(mask, edma_filter_fn,
> > drivers/spi/spi-davinci.c:      dspi->dma_tx = dma_request_channel(mask, edma_filter_fn,
> >
> > As long as this is the case, you have to be careful with the dependencies
> > to make sure that davinci_mmc and spi-davinci either depend on TI_EDMA, or
> > edma_filter_fn gets defined to NULL when you are building for a DT-only platform.
> 
> Yes sure, right now they are defined  as follows in include/linux/edma.h:
> 
> #if defined(CONFIG_TI_EDMA) || defined(CONFIG_TI_EDMA_MODULE)
> bool edma_filter_fn(struct dma_chan *, void *);
> #else
> static inline bool edma_filter_fn(struct dma_chan *chan, void *param)
> {
> return false;
> }
> #endif

It's best to just define the filter function in the platform
code and pass a pointer to it through platform data. The way you do
it above makes the slave drivers inherently nonportable.

	Arnd
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