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Date: Fri, 21 Jun 2013 21:53:18 -0500
Message-ID: <CAD=GYpabakChmN-TEJbLn6p=BwX2wsK5KWsc5gH9-cAA+yWcEA@mail.gmail.com>
Subject: Re: [PATCH v12 05/11] edma: config: Enable config options for EDMA
From: Joel A Fernandes <agnel.joel@gmail.com>
To: Arnd Bergmann <arnd@arndb.de>
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>,
        Mark Brown <broonie@opensource.wolfsonmicro.com>,
        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>,
        Devicetree Discuss <devicetree-discuss@lists.ozlabs.org>,
        Linux OMAP List <linux-omap@vger.kernel.org>,
        Linux ARM Kernel List <linux-arm-kernel@lists.infradead.org>,
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	<davinci-linux-open-source@linux.davincidsp.com>,
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>> > 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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