linux-kernel - Re: [PATCH] mmc: spi: disable dma mapping code, as it does not work

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Date:   Tue, 23 May 2017 09:58:07 +0200
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Phil Elwell <phil@...pberrypi.org>
Cc:     Martin Sperl <kernel@...tin.sperl.org>,
        Heiner Kallweit <hkallweit1@...il.com>,
        "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mmc: spi: disable dma mapping code, as it does not work

On 22 May 2017 at 11:09, Phil Elwell <phil@...pberrypi.org> wrote:
> since:
>         commit 0589342c27944e50ebd7a54f5215002b6598b748
>         Author: Rob Herring <rob.herring@...xeda.com>
>         Date:   Tue Oct 29 23:36:46 2013 -0500
>
>              of: set dma_mask to point to coherent_dma_mask
>
>              Platform devices created by DT code don't initialize dma_mask pointer to
>              anything. Set it to coherent_dma_mask by default if the architecture
>              code has not set it.
>
> the mmc-spi driver no longer detects the sd-cards any longer.
>
> This patch disables the offending section in mmc_spi
> so that the driver works again and detects the sd card normally.
>
> There is no real negative impact as the spi-framework
> does no longer rely on driver-provided DMA mappings but
> maps the transfers transparently.
>
> Signed-off-by: Martin Sperl <kernel@...tin.sperl.org>
> Submitted-by: Phil Elwell <phil@...pberrypi.org>
> ---
>  drivers/mmc/host/mmc_spi.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)
>
> diff --git a/drivers/mmc/host/mmc_spi.c b/drivers/mmc/host/mmc_spi.c
> index ae19d83bb9de0..16946e2513afa 100644
> --- a/drivers/mmc/host/mmc_spi.c
> +++ b/drivers/mmc/host/mmc_spi.c
> @@ -1387,6 +1387,16 @@ static int mmc_spi_probe(struct spi_device *spi)
>         if (!host->data)
>                 goto fail_nobuf1;
>
> +       /* for some reason mmc_spi does not work with this enabled
> +        * it is not needed anyway, as the SPI framework does DMA
> +        * transfers now automatically
> +        * the patch that introduced this was:
> +        * commit 0589342c27944e50ebd7a54f5215002b6598b748
> +        * Author: Rob Herring <rob.herring@...xeda.com>
> +        * Date:   Tue Oct 29 23:36:46 2013 -0500
> +        *      of: set dma_mask to point to coherent_dma_mask
> +        */
> +#if 0
>         if (spi->master->dev.parent->dma_mask) {
>                 struct device   *dev = spi->master->dev.parent;
>
> @@ -1402,6 +1412,7 @@ static int mmc_spi_probe(struct spi_device *spi)
>                                 host->data_dma, sizeof(*host->data),
>                                 DMA_BIDIRECTIONAL);
>         }
> +#endif
>
>         /* setup message for status/busy readback */
>         spi_message_init(&host->readback);

Phil, I am not sure how to go with this.

Your change drops the dma implementation in the mmc_spi driver as
host->dma_dev now never gets assigned. I do think that makes sense as
the dma support should be implemented in the spi master driver and not
in the spi client driver, which currently is the case for mmc_spi.

Then perhaps a more proper change would be to remove the dma
implementation in mmc_spi altogether?

And one more thing, next time also cc the spi-list and Mark Brown, to
try to some broader input.

Kind regards
Uffe