Re: git: ea130fa32099 - main - virtio_net: Use bus_dma for command/ack buffers

On 18 Jun 2026, at 09:05, Andrew Turner <andrew@FreeBSD.org> wrote:
> 
> The branch main has been updated by andrew:
> 
> URL: https://cgit.FreeBSD.org/src/commit/?id=ea130fa32099ea7e0c03702efdec28e745ea6ef1
> 
> commit ea130fa32099ea7e0c03702efdec28e745ea6ef1
> Author:     Sarah Walker <sarah.walker2@arm.com>
> AuthorDate: 2026-02-27 14:17:15 +0000
> Commit:     Andrew Turner <andrew@FreeBSD.org>
> CommitDate: 2026-06-18 16:04:24 +0000
> 
>    virtio_net: Use bus_dma for command/ack buffers
> 
>    While the majority of virtio platforms will be fully coherent, some may
>    require cache maintenance or other specific device memory handling (eg for
>    secure partitioning). Using bus_dma allows for these usecases.
> 
>    The virtio buffers are marked as coherent; this should ensure that sync
>    calls are no-ops in the common cases.
> 
>    Reviewed by:    andrew
>    Sponsored by:   Arm Ltd
>    Differential Revision:  https://reviews.freebsd.org/D55564
> —--
> [...]
> @@ -523,14 +523,60 @@ vtnet_attach(device_t dev)
> goto fail;
> }
> 
> + mtx_init(&sc->vtnet_hdr_mtx, device_get_nameunit(dev),
> +    "VirtIO Net header lock", MTX_DEF);
> +
> + error = bus_dma_tag_create(
> +    bus_get_dma_tag(dev), /* parent */
> +    sizeof(uint16_t), /* alignment */
> +    0, /* boundary */
> +    BUS_SPACE_MAXADDR, /* lowaddr */
> +    BUS_SPACE_MAXADDR, /* highaddr */
> +    NULL, NULL, /* filter, filterarg */
> +    PAGE_SIZE, /* max request size */
> +    1, /* max # segments */
> +    PAGE_SIZE, /* maxsegsize */
> +    BUS_DMA_COHERENT, /* flags */
> +    busdma_lock_mutex, /* lockfunc */
> +    &sc->vtnet_hdr_mtx, /* lockarg */
> +    &sc->vtnet_hdr_dmat);
> + if (error) {
> + device_printf(dev, "cannot create bus_dma_tag\n");
> + goto fail;
> + }
> +
> + mtx_init(&sc->vtnet_ack_mtx, device_get_nameunit(dev),
> +    "VirtIO Net ACK lock", MTX_DEF);
> +
> + error = bus_dma_tag_create(
> +    bus_get_dma_tag(dev), /* parent */
> +    sizeof(uint8_t), /* alignment */
> +    0, /* boundary */
> +    BUS_SPACE_MAXADDR, /* lowaddr */
> +    BUS_SPACE_MAXADDR, /* highaddr */
> +    NULL, NULL, /* filter, filterarg */
> +    sizeof(uint8_t), /* max request size */
> +    1, /* max # segments */
> +    sizeof(uint8_t), /* maxsegsize */
> +    BUS_DMA_COHERENT, /* flags */
> +    busdma_lock_mutex, /* lockfunc */
> +    &sc->vtnet_ack_mtx, /* lockarg */
> +    &sc->vtnet_ack_dmat);
> + if (error) {
> + device_printf(dev, "cannot create bus_dma_tag\n");
> + goto fail;
> + }
> +
> #ifdef __powerpc__
> - /*
> - * Virtio uses physical addresses rather than bus addresses, so we
> - * need to ask busdma to skip the iommu physical->bus mapping.  At
> - * present, this is only a thing on the powerpc architectures.
> - */
> - bus_dma_tag_set_iommu(sc->vtnet_rx_dmat, NULL, NULL);
> - bus_dma_tag_set_iommu(sc->vtnet_tx_dmat, NULL, NULL);
> +        /*
> +         * Virtio uses physical addresses rather than bus addresses, so we
> +         * need to ask busdma to skip the iommu physical->bus mapping.  At
> +         * present, this is only a thing on the powerpc architectures.
> +         */
> +        bus_dma_tag_set_iommu(sc->vtnet_rx_dmat, NULL, NULL);
> +        bus_dma_tag_set_iommu(sc->vtnet_tx_dmat, NULL, NULL);
> +        bus_dma_tag_set_iommu(sc->vtnet_hdr_dmat, NULL, NULL);
> +        bus_dma_tag_set_iommu(sc->vtnet_ack_dmat, NULL, NULL);
> #endif

This block has been re-indented to use spaces not tabs.

Jessica