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

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Message-ID: <CAD=GYpYrkE--Snc-MoEdJRkUy5TfMY992kd0L--E6yPpMoRaxQ@mail.gmail.com>
Date:	Mon, 24 Jun 2013 09:48:37 -0500
From:	Joel A Fernandes <agnel.joel@...il.com>
To:	Sekhar Nori <nsekhar@...com>
Cc:	Arnd Bergmann <arnd@...db.de>, 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 Mon, Jun 24, 2013 at 6:53 AM, Sekhar Nori <nsekhar@...com> wrote:
> On 6/22/2013 8:23 AM, 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
>>
>> 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.
>
> Solution for this is to enable TI_EDMA in relevant defconfigs. Most
> folks who would get frustrated by such issues would be using defconfigs
> and for those who are building their configuration from scratch this
> will be pretty low in their list of worries.

Yes, it is not in omap2plus_defconfig either. I will post a patch to
add it to the same, and we can ignore the Kconfig defaults and select
patches.

Thanks,
Joel
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