Re: [PATCH v4 5/9] iommu/vt-d: Don't switch off swiotlb if use direct dma

[Lu Baolu]

Hi,

On 6/10/19 11:54 PM, Konrad Rzeszutek Wilk wrote:

On Mon, Jun 03, 2019 at 09:16:16AM +0800, Lu Baolu wrote:

The direct dma implementation depends on swiotlb. Hence, don't
switch of swiotlb since direct dma interfaces are used in this

s/of/off/

Yes.

driver.

But I think you really want to leave the code as is but change
the #ifdef to check for IOMMU_BOUNCE_PAGE and not CONFIG_SWIOTLB.

As one could disable IOMMU_BOUNCE_PAGE.

SWIOTLB is not only used when IOMMU_BOUCE_PAGE is enabled.

Please check this code:

static dma_addr_t intel_map_page(struct device *dev, struct page *page,
                                 unsigned long offset, size_t size,
                                 enum dma_data_direction dir,
                                 unsigned long attrs)
{
        if (iommu_need_mapping(dev))
                return __intel_map_single(dev, page_to_phys(page) + offset,
                                size, dir, *dev->dma_mask);
        return dma_direct_map_page(dev, page, offset, size, dir, attrs);
}

The dma_direct_map_page() will eventually call swiotlb_map() if the
buffer is beyond the address capability of the device.

Best regards,
Baolu

Cc: Ashok Raj <ashok....@intel.com>
Cc: Jacob Pan <jacob.jun....@linux.intel.com>
Cc: Kevin Tian <kevin.t...@intel.com>
Cc: Mika Westerberg <mika.westerb...@intel.com>
Signed-off-by: Lu Baolu <baolu...@linux.intel.com>
---
  drivers/iommu/intel-iommu.c | 6 ------
  1 file changed, 6 deletions(-)

diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
index d5a6c8064c56..235837c50719 100644
--- a/drivers/iommu/intel-iommu.c
+++ b/drivers/iommu/intel-iommu.c
@@ -4625,9 +4625,6 @@ static int __init platform_optin_force_iommu(void)
                iommu_identity_mapping |= IDENTMAP_ALL;

dmar_disabled = 0;

-#if defined(CONFIG_X86) && defined(CONFIG_SWIOTLB)
-       swiotlb = 0;
-#endif
        no_iommu = 0;

return 1;

@@ -4765,9 +4762,6 @@ int __init intel_iommu_init(void)
        }
        up_write(&dmar_global_lock);

-#if defined(CONFIG_X86) && defined(CONFIG_SWIOTLB)

-       swiotlb = 0;
-#endif
        dma_ops = &intel_dma_ops;

init_iommu_pm_ops();

--
2.17.1