From mboxrd@z Thu Jan  1 00:00:00 1970
From: Adrian Hunter <adrian.hunter@intel.com>
Subject: Re: [PATCH V2] mmc: sdhci-acpi: Add 64-bit DMA support
Date: Tue, 28 Oct 2014 12:05:30 +0200
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To: Arnd Bergmann <arnd@arndb.de>
Cc: Ulf Hansson <ulf.hansson@linaro.org>, Chris Ball <chris@printf.net>, linux-mmc <linux-mmc@vger.kernel.org>

On 28/10/14 11:43, Arnd Bergmann wrote:
> On Tuesday 28 October 2014 10:37:20 Adrian Hunter wrote:
>>  static int sdhci_acpi_enable_dma(struct sdhci_host *host)
>>  {
>> -       return 0;
>> +       struct sdhci_acpi_host *c = sdhci_priv(host);
>> +       struct device *dev = &c->pdev->dev;
>> +       int err = -1;
>> +
>> +       if (c->dma_setup)
>> +               return 0;
>> +
>> +       if (host->flags & SDHCI_USE_64_BIT_DMA) {
>> +               if (host->quirks2 & SDHCI_QUIRK2_BROKEN_64_BIT_DMA) {
>> +                       host->flags &= ~SDHCI_USE_64_BIT_DMA;
>> +               } else {
>> +                       err = dma_set_mask_and_coherent(dev, DMA_BIT_MASK(64));
>> +                       if (err)
>> +                               dev_warn(dev, "Failed to set 64-bit DMA mask\n");
>> +               }
>> +       }
>> +
>> +       if (err)
>> +               err = dma_set_mask_and_coherent(dev, DMA_BIT_MASK(32));
>> +
>> +       c->dma_setup = !err;
>> +
>> +       return err;
>>  }
>>
> 
> I don't think it's worth a dev_warn() message (maybe dev_info), there is nothing

It is worth a dev_warn because 32-bit DMA can allocate memory for bounce
buffers which jeopardizes memory reclaim.

> wrong in this case, but you probably have to clear the SDHCI_USE_64_BIT_DMA to
> ensure that the driver won't try to to use the 64-bit DMA if the mask is not set.

64-bit DMA will work with a 32-bit DMA mask so there is no need.