Re: [PATCH 6/6] virtio: add api virtio_dma_map() for advance dma

["Michael S. Tsirkin" <mst@redhat.com>]

On Fri, Jan 07, 2022 at 02:33:06PM +0800, Xuan Zhuo wrote:
> Added virtio_dma_map() to map DMA addresses for virtual memory in
> advance. The purpose of adding this function is to check
> vring_use_dma_api() for virtio dma operation and get vdev->dev.parent as
> the parameter of dma_map_page().
> 
> Added virtio_dma_unmap() for unmap DMA address.
> 
> Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>


OK but where are the users for this new API?


> ---
>  drivers/virtio/virtio_ring.c | 47 ++++++++++++++++++++++++++++++++++++
>  include/linux/virtio.h       |  9 +++++++
>  2 files changed, 56 insertions(+)
> 
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index e165bc2e1344..f4a0fb85df27 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -2472,4 +2472,51 @@ const struct vring *virtqueue_get_vring(struct virtqueue *vq)
>  }
>  EXPORT_SYMBOL_GPL(virtqueue_get_vring);
>  
> +/**
> + * virtio_dma_map - get the DMA addr of the memory for virtio device
> + * @vdev: virtio device
> + * @page: the page of the memory to DMA
> + * @offset: the offset of the memory inside page
> + * @length: memory length
> + * @dir: DMA direction
> + *
> + * Returns the DMA addr. Zero means error.

Should not drivers use a variant of dma_mapping_error to check?

> + */
> +dma_addr_t virtio_dma_map(struct virtio_device *vdev,
> +			  struct page *page, size_t offset,
> +			  unsigned int length,
> +			  enum dma_data_direction dir)
> +{
> +	dma_addr_t addr;
> +
> +	if (!vring_use_dma_api(vdev))
> +		return page_to_phys(page) + offset;
> +
> +	addr = dma_map_page(vdev->dev.parent, page, offset, length, dir);
> +
> +	if (dma_mapping_error(vdev->dev.parent, addr))
> +		return 0;
> +
> +	return addr;
> +}
> +EXPORT_SYMBOL_GPL(virtio_dma_map);


Yes it's 0, but you should really use DMA_MAPPING_ERROR.

> +
> +/**
> + * virtio_dma_unmap - unmap DMA addr
> + * @vdev: virtio device
> + * @dma: DMA address
> + * @length: memory length
> + * @dir: DMA direction
> + */
> +void virtio_dma_unmap(struct virtio_device *vdev,
> +		      dma_addr_t dma, unsigned int length,
> +		      enum dma_data_direction dir)
> +{
> +	if (!vring_use_dma_api(vdev))
> +		return;
> +
> +	dma_unmap_page(vdev->dev.parent, dma, length, dir);
> +}
> +EXPORT_SYMBOL_GPL(virtio_dma_unmap);
> +
>  MODULE_LICENSE("GPL");
> diff --git a/include/linux/virtio.h b/include/linux/virtio.h
> index 41edbc01ffa4..6e6c6e18ecf8 100644
> --- a/include/linux/virtio.h
> +++ b/include/linux/virtio.h
> @@ -9,6 +9,7 @@
>  #include <linux/device.h>
>  #include <linux/mod_devicetable.h>
>  #include <linux/gfp.h>
> +#include <linux/dma-mapping.h>
>  
>  /**
>   * virtqueue - a queue to register buffers for sending or receiving.
> @@ -195,4 +196,12 @@ void unregister_virtio_driver(struct virtio_driver *drv);
>  #define module_virtio_driver(__virtio_driver) \
>  	module_driver(__virtio_driver, register_virtio_driver, \
>  			unregister_virtio_driver)
> +
> +dma_addr_t virtio_dma_map(struct virtio_device *vdev,
> +			  struct page *page, size_t offset,
> +			  unsigned int length,
> +			  enum dma_data_direction dir);
> +void virtio_dma_unmap(struct virtio_device *vdev,
> +		      dma_addr_t dma, unsigned int length,
> +		      enum dma_data_direction dir);
>  #endif /* _LINUX_VIRTIO_H */
> -- 
> 2.31.0

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