Re: [PATCH 13/15] mmc: sdhci-acpi: Add 64-bit DMA support

[Arnd Bergmann <arnd@arndb.de>]

On Tuesday 21 October 2014 13:45:20 Adrian Hunter wrote:
> On 21/10/14 12:33, Arnd Bergmann wrote:
> > On Tuesday 21 October 2014 12:26:23 Adrian Hunter wrote:
> >> +               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_coerce_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_coerce_mask_and_coherent(dev, DMA_BIT_MASK(32));
> >> +
> >> +       c->dma_setup = !err;
> >>
> > 
> > Never use dma_coerce_mask_and_coherent(), it will ignore limitations of
> > the upstream bus. Use dma_set_mask_and_coherent instead. If it fails,
> > I think you need to clear the SDHCI_USE_64_BIT_DMA flag.
> 
> The sdhci-acpi device is a  platform devices created by acpi.  dev->dma_mask
> is NULL so dma_set_mask_and_coherent will always fail
> unless I add:
> 
>         if (!dev->dma_mask)
>                 dev->dma_mask = &dev->coherent_dma_mask;
> 

That's a bug in the ACPI code. Fix that instead of working around it in random
drivers.

	Arnd