From: Arnd Bergmann <arnd@arndb.de>
To: Joel A Fernandes <agnel.joel@gmail.com>
Subject: Re: [PATCH v12 05/11] edma: config: Enable config options for EDMA
Date: Mon, 24 Jun 2013 22:28:23 +0200
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Cc: Sekhar Nori <nsekhar@ti.com>, Joel A Fernandes <joelagnel@ti.com>,
        Tony Lindgren <tony@atomide.com>, Matt Porter <matt@ohporter.com>,
        Grant Likely <grant.likely@secretlab.ca>,
        Rob Herring <rob.herring@calxeda.com>,
        Vinod Koul <vinod.koul@intel.com>,
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        Benoit Cousson <b-cousson@ti.com>,
        Russell King <linux@arm.linux.org.uk>, Rob Landley <rob@landley.net>,
        Andrew Morton <akpm@linux-foundation.org>,
        Jason Kridner <jkridner@beagleboard.org>,
        Koen Kooi <koen@beagleboard.org>,
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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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