Messages in this thread | | | Date | Wed, 8 Dec 2021 08:35:49 -0700 | Subject | Re: [PATCH 4/4] dmaengine: idxd: Use DMA API for in-kernel DMA with PASID | From | Dave Jiang <> |
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On 12/8/2021 6:13 AM, Jason Gunthorpe wrote: > On Tue, Dec 07, 2021 at 05:47:14AM -0800, Jacob Pan wrote: >> In-kernel DMA should be managed by DMA mapping API. The existing kernel >> PASID support is based on the SVA machinery in SVA lib that is intended >> for user process SVA. The binding between a kernel PASID and kernel >> mapping has many flaws. See discussions in the link below. >> >> This patch utilizes iommu_enable_pasid_dma() to enable DSA to perform DMA >> requests with PASID under the same mapping managed by DMA mapping API. >> In addition, SVA-related bits for kernel DMA are removed. As a result, >> DSA users shall use DMA mapping API to obtain DMA handles instead of >> using kernel virtual addresses. > Er, shouldn't this be adding dma_map/etc type calls? > > You can't really say a driver is using the DMA API without actually > calling the DMA API.. > >> + /* >> + * Try to enable both in-kernel and user DMA request with PASID. >> + * PASID is supported unless both user and kernel PASID are >> + * supported. Do not fail probe here in that idxd can still be >> + * used w/o PASID or IOMMU. >> + */ >> + if (iommu_dev_enable_feature(dev, IOMMU_DEV_FEAT_SVA) || >> + idxd_enable_system_pasid(idxd)) { >> + dev_warn(dev, "Failed to enable PASID\n"); >> + } else { >> + set_bit(IDXD_FLAG_PASID_ENABLED, &idxd->flags); >> } > Huh? How can the driver keep going if PASID isn't supported? I thought > the whole point of this was because the device cannot do DMA without > PASID at all?
There are 2 types of WQ supported with the DSA devices. A dedicated WQ type and a shared WQ type. The dedicated WQ type can support DMA with and without PASID. The shared wq type must have a PASID to operate. The driver can support dedicated WQ only without PASID usage when there is no PASID support.
> > Jason
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