Re: [PATCH 1/1] mmc: host: enable OMAP DMA engine support for omap hosts by default

["Shilimkar, Santosh" <santosh.shilimkar@ti.com>]

On Wed, Jul 18, 2012 at 1:14 PM, S, Venkatraman <svenkatr@ti.com> wrote:
> On Wed, Jul 18, 2012 at 12:40 PM, Tony Lindgren <tony@atomide.com> wrote:
>> * Shilimkar, Santosh <santosh.shilimkar@ti.com> [120718 00:09]:
>>> On Wed, Jul 18, 2012 at 12:29 PM, Tony Lindgren <tony@atomide.com> wrote:
>>> > * Javier Martinez Canillas <javier@dowhile0.org> [120716 23:56]:
>>> >> On Tue, Jul 17, 2012 at 8:45 AM, Shilimkar, Santosh
>>> >> <santosh.shilimkar@ti.com> wrote:
>>> >> > Hi,
>>> >> >
>>> >> > On Tue, Jul 17, 2012 at 6:00 AM, Javier Martinez Canillas
>>> >> > <javier@dowhile0.org> wrote:
>>> >> >> The OMAP MMC and OMAP High Speed MMC hosts now use entirely the DMA
>>> >> >> engine API instead of the previous private DMA API implementation.
>>> >> >>
>>> >> >> So, if the kernel is built with support for any of these hosts but it
>>> >> >> doesn't support DMA devices nor OMAP DMA support, it fails when trying
>>> >> >> to obtain a DMA channel which leads to the following error on an OMAP3
>>> >> >> IGEPv2 Rev.C board (and probably on most OMAP boards with MMC support):
>>> >> >>
>>> >> >> [    2.199981] omap_hsmmc omap_hsmmc.1: unable to obtain RX DMA engine channel 48
>>> >> >> [    2.215087] omap_hsmmc omap_hsmmc.0: unable to obtain RX DMA engine channel 62
>>> >> >>
>>> >> >> selecting automatically CONFIG_DMADEVICES and CONFIG_DMA_OMAP solves it.
>>> >> >>
>>> >> >> Signed-off-by: Javier Martinez Canillas <javier@dowhile0.org>
>>> >> >> ---
>>> >> > Considering, we are updating drivers to select the DMA engine, can you
>>> >> > also include
>>> >> > "drivers/spi/spi-omap2-mcspi.c" which is also updated for DMA engine.
>>> >> >
>>> >> > Regards
>>> >> > Santosh
>>> >>
>>> >> Hi Santosh,
>>> >>
>>> >> Ok, I'll send a v2 now which includes spi-omap2-mcspi then.
>>> >
>>> > I don't think we should do this, the drivers should work with and without
>>> > dma. This just needs to be added to the omap2plus_defconfig.
>>> >
>>> Well this was not decided based on any DMA CONFIG option before for
>>> the subject drivers. It is already by default enabled if the DMA is supported
>>> by the driver IP. There is a possibility to disable it from driver platform/dt
>>> data so that still remains.
>>
>> I think it should rather be that if the driver is broken and does not work
>> without DMA, it should have depends on CONFIG_DMA_OMAP.
>>
> I can confirm that omap MMC can't work without DMA; polled mode is not
> supported / implemented.

Same case for SPI driver as well. It uses DMA for everything except the cases
where DMA doesn't make sense like 1 byte/2 byte etc. And its not configurable,

At least considering this, it is better we do this per driver than enabling
it at SOC config.

Regards
Santosh