Re: [PATCH 4/8] MMC: add DMA support to tmio_mmc driver, when used on

[Magnus Damm <magnus.damm@gmail.com>]

Hi Guennadi,

On Wed, Apr 21, 2010 at 11:37 AM, Guennadi Liakhovetski
<g.liakhovetski@gmx.de> wrote:
> SDHI controllers on SuperH, served by the tmio_mmc driver, can use slave DMA
> for data transfer. This patch adds support for the dmaengine API to tmio_mmc
> and the necessary interfacing to the sh_mobile_sdhi MFD driver.
>
> Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
> ---
>
> It could be further broken down into MMC and MFD parts if required, I
> think.
>
>  drivers/mfd/sh_mobile_sdhi.c       |   25 +++-
>  drivers/mmc/host/tmio_mmc.c        |  346 ++++++++++++++++++++++++++++++++----
>  drivers/mmc/host/tmio_mmc.h        |   11 ++
>  include/linux/mfd/sh_mobile_sdhi.h |    3 +
>  include/linux/mfd/tmio.h           |   10 +
>  5 files changed, 359 insertions(+), 36 deletions(-)

[snip]

> diff --git a/drivers/mmc/host/tmio_mmc.c b/drivers/mmc/host/tmio_mmc.c
> index b2b577f..fafd8c9 100644
> --- a/drivers/mmc/host/tmio_mmc.c
> +++ b/drivers/mmc/host/tmio_mmc.c
> @@ -29,12 +29,21 @@
>  #include <linux/irq.h>
>  #include <linux/device.h>
>  #include <linux/delay.h>
> +#include <linux/dmaengine.h>
>  #include <linux/mmc/host.h>
>  #include <linux/mfd/core.h>
>  #include <linux/mfd/tmio.h>
>
>  #include "tmio_mmc.h"
>
> +static void tmio_mmc_enable_dma(struct tmio_mmc_host *host, bool enable)
> +{
> +#if defined(CONFIG_SUPERH) || defined(CONFIG_ARCH_SHMOBILE)
> +       /* Switch DMA mode on or off - SuperH specific? */
> +       sd_ctrl_write16(host, 0xd8, enable ? 2 : 0);
> +#endif
> +}
> +

Uhh.. #ifdefs. =)

Can't this register setting be implented in the SDHI driver?

In general I realize that you need to extend the logic in the tmio_mmc
driver quite a bit to implement DMA support, but I wonder if it is
possible to extend the tmio_mmc driver with callbacks and use them to
hook in the DMA code?

Thanks!

/ magnus