Re: [RFC PATCH 09/11] drivers: acpi: implement acpi_dma_configure

[Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>]

On Fri, Apr 15, 2016 at 01:29:14PM -0500, Timur Tabi wrote:
> On Thu, Apr 14, 2016 at 12:25 PM, Lorenzo Pieralisi
> <lorenzo.pieralisi@arm.com> wrote:
> > +void acpi_dma_configure(struct device *dev, enum dev_dma_attr attr)
> > +{
> > +       struct iommu_ops *iommu;
> > +
> > +       iommu = iort_iommu_configure(dev);
> > +
> > +       /*
> > +        * Assume dma valid range starts at 0 and covers the whole
> > +        * coherent_dma_mask.
> > +        */
> > +       arch_setup_dma_ops(dev, 0, dev->coherent_dma_mask + 1, iommu,
> > +                          attr == DEV_DMA_COHERENT);
> > +}
> 
> I have a network driver that is impacted by this code, so thank you
> for posting this. (See
> https://www.mail-archive.com/netdev@vger.kernel.org/msg106249.html).
> 
> One one SOC, the driver needs to set the mask to 32 bits.  On another
> SOC, it needs to set it to 64 bits.  On device tree, the driver will
> use dma-ranges.

First off I think we agree this patch does not change current behaviour
as far as the devices default dma_mask are concerned. They are
initialized in PCI/ACPI core code:

- pci_setup_device()
- acpi_create_platform_device()

As for ACPI DT-dma-ranges equivalent I have to check if I can use
the _DMA method for that so that we can put in place the same
mechanism as DT to override the default masks, other than that it is
up to the drivers to set-up the dma mask accordingly, that's not
something this patchset is changing anyway.

> In your patches, where is coherent_dma_mask initialized?  I found this
> code in add_smmu_platform_device(), but I think this is setting the
> mask for the IOMMU driver, not the individual devices.  Either way, I
> don't understand where the correct value is going to be overridden.

For the ARM SMMU table walker:

arm_smmu_device_cfg_probe() - dma_set_mask_and_coherent()

For other devices see above.

Thanks,
Lorenzo

> 
> +       /*
> +        * Set default dma mask value for the table walker,
> +        * to be overridden on probing with correct value.
> +        */
> +       *pdev->dev.dma_mask = DMA_BIT_MASK(32);
> +       pdev->dev.coherent_dma_mask = *pdev->dev.dma_mask;
> 
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