linux-kernel - Re: [PATCH v12 05/11] edma: config: Enable config options for EDMA

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Date:	Fri, 21 Jun 2013 21:53:18 -0500
From:	Joel A Fernandes <agnel.joel@...il.com>
To:	Arnd Bergmann <arnd@...db.de>
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

>> > 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

This also has the side effect of causing DMA requests to fail if
TI_EDMA is not built, causing frustration for a lot of people some of
whom don't want to deal with DMA so I think it is OK to build the
driver in by default as it is (and will be) used by a lot of
OMAP2PLUS.

Thanks,
Joel
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