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

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Message-ID: <205f0c9b-1037-437d-f87f-c51c0b58313a@raspberrypi.org>
Date:   Tue, 23 May 2017 11:11:40 +0100
From:   Phil Elwell <phil@...pberrypi.org>
To:     Ulf Hansson <ulf.hansson@...aro.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 23/05/2017 08:58, Ulf Hansson wrote:
> 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?

I don't have enough in-depth SPI knowledge to make that decision - I'm happy to go
with what the SPI experts recommend.

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

Thanks for the tip, Ulf - I just went with what scripts/get_maintainer.pl suggested.
Perhaps that list needs to be updated?

Phil