Re: [PATCH V2] mmc: sdhci-acpi: Add 64-bit DMA support

Adrian Hunter
2014-10-28T14:14:52Z

On 28/10/2014 3:54 p.m., Arnd Bergmann wrote:
> On Tuesday 28 October 2014 13:41:30 Adrian Hunter wrote:
>> On 28/10/14 12:18, Arnd Bergmann wrote:
>>> On Tuesday 28 October 2014 12:05:30 Adrian Hunter wrote:
>>>> 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.
>>>
>>> Then you should also warn if SDHCI_USE_64_BIT_DMA isn't or if
>>> SDHCI_QUIRK2_BROKEN_64_BIT_DMA is set I guess.
>>
>> The warning is for when the controller supports 64-bit, not when it doesn't.
>
> But why warn about a feature of the controller being present? You just
> said it's a problem for memory reclaim if 64-bit DMA is not supported.

The warning is for when the controller supports 64-bit but it can't
get a 64-bit DMA mask, and might therefore need to bounce things.