[RFC PATCH 09/11] drivers: acpi: implement acpi_dma_configure
robin.murphy at arm.com
Mon Apr 18 03:43:38 PDT 2016
On 15/04/16 19:29, Timur Tabi wrote:
> On Thu, Apr 14, 2016 at 12:25 PM, Lorenzo Pieralisi
> <lorenzo.pieralisi at 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
> 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.
That's the wrong way to look at it - the driver isn't _using_
dma-ranges, you're merely relying on the OF code setting the _default_
DMA mask differently based on the property. If your driver is in the
minority of those which actually care about DMA masks, then it should be
calling dma_set_mask_and_coherent() appropriately and not relying on the
> 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.
Yes, that's for the SMMU itself as a device (i.e. the page table walker)
- as a handy example of "drivers which actually care about DMA masks",
it specifically needs to avoid a too-small DMA mask because
bounce-buffering the page tables tends to make things go horribly wrong.
> Either way, I
> don't understand where the correct value is going to be overridden.
> + /*
> + * 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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