Messages in this thread | | | Date | Wed, 8 Dec 2021 13:51:16 -0400 | From | Jason Gunthorpe <> | Subject | Re: [PATCH 4/4] dmaengine: idxd: Use DMA API for in-kernel DMA with PASID |
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On Wed, Dec 08, 2021 at 08:35:49AM -0700, Dave Jiang wrote: > > 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.
Can you add to the cover letter why does the kernel require to use the shared WQ?
Jason
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