On Tue, 11 Apr 2023 05:16:19 -0700, Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote: > On Tue, Apr 11, 2023 at 03:23:43PM +0800, Xuan Zhuo wrote: > > > If a direct map or not is used is a decision done by the platform code, > > > often based on firmware tables. You can't just override that. > > > > > > Can Virtio Device set its own dma_ops? It is a device on the virtual bus. It > > sets its own DMA_OPS. I think it is reasonable. > > No, it can't. virtio devices are backed by PCI, platform or other > bus devices, and the (often virtual) firmware controls how DMA mapping > is to be performed for them, at least for the platform_access case. Sorry, rethink about this, I think we maybe misunderstand something. First of all, let me give you a brief introduce of virtio device and pci device. If I make mistake, please point out. First, when one virtio pci device is probed, then the virtio pci driver will be called. Then we got one pci_device. Then virtio_pci_probe will alloc one new device, and register it to virtio bus by register_virtio_device(). So here we have two device: pci-device and virtio-device. If we call DMA API inside virtio, we use the pci-device. The virtio-device is not used for DMA API. Now we want to use the virtio-device to do direct dma. The virtio-device is created by virtio_pci_probe() of virtio pci driver. And register to virtio bus. So no firmware and not iommu and the bus is virtio bus, why we can not change the dma_ops of virtio-device? Thanks. _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
