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

Arnd Bergmann
2014-10-28T13:54:55Z

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.

Arnd