Subject: Re: [PATCH 07/33] virtio_ring: add api virtio_dma_map() for advance dma

From: "Michael S. Tsirkin" <[email-masked]>
Date: Fri, 3 Feb 2023 04:07:10 -0500

On Thu, Feb 02, 2023 at 07:00:32PM +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().

No this looks like the implementation not the purpose.
I am guessing the purpose is to keep memory mapped
across multiple add/get buf operations right?

> Added virtio_dma_unmap() for unmap DMA address.
> 
> Signed-off-by: Xuan Zhuo <[email-masked]>
> ---
>  drivers/virtio/virtio_ring.c | 80 ++++++++++++++++++++++++++++++++++++
>  include/linux/virtio.h       |  9 ++++
>  2 files changed, 89 insertions(+)
> 
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index 7dfce7001f9f..67eda7bc23ea 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -3022,4 +3022,84 @@ const struct vring *virtqueue_get_vring(struct virtqueue *vq)
>  }
>  EXPORT_SYMBOL_GPL(virtqueue_get_vring);
>  
> +/**
> + * virtio_dma_map_page - get the DMA addr of the memory for virtio device
> + * @dev: 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. DMA_MAPPING_ERROR means error.
> + */
> +dma_addr_t virtio_dma_map_page(struct device *dev, struct page *page, size_t offset,
> +			       unsigned int length, enum dma_data_direction dir)
> +{
> +	struct virtio_device *vdev = dev_to_virtio(dev);
> +
> +	if (!vring_use_dma_api(vdev))
> +		return page_to_phys(page) + offset;
> +
> +	return dma_map_page(vdev->dev.parent, page, offset, length, dir);
> +}
> +
> +/**
> + * virtio_dma_map - get the DMA addr of the memory for virtio device
> + * @dev: virtio device
> + * @addr: the addr to DMA
> + * @length: memory length
> + * @dir: DMA direction
> + *
> + * Returns the DMA addr.
> + */
> +dma_addr_t virtio_dma_map(struct device *dev, void *addr, unsigned int length,
> +			  enum dma_data_direction dir)
> +{
> +	struct page *page;
> +	size_t offset;
> +
> +	page = virt_to_page(addr);
> +	offset = offset_in_page(addr);
> +
> +	return virtio_dma_map_page(dev, page, offset, length, dir);
> +}
> +EXPORT_SYMBOL_GPL(virtio_dma_map);
> +
> +/**
> + * virtio_dma_mapping_error - check dma address
> + * @dev: virtio device
> + * @addr: DMA address
> + *
> + * Returns 0 means dma valid. Other means invalid dma address.
> + */
> +int virtio_dma_mapping_error(struct device *dev, dma_addr_t addr)
> +{
> +	struct virtio_device *vdev = dev_to_virtio(dev);
> +
> +	if (!vring_use_dma_api(vdev))
> +		return 0;
> +
> +	return dma_mapping_error(vdev->dev.parent, addr);
> +}
> +EXPORT_SYMBOL_GPL(virtio_dma_mapping_error);
> +
> +/**
> + * virtio_dma_unmap - unmap DMA addr
> + * @dev: virtio device
> + * @dma: DMA address
> + * @length: memory length
> + * @dir: DMA direction
> + */
> +void virtio_dma_unmap(struct device *dev, dma_addr_t dma, unsigned int length,
> +		      enum dma_data_direction dir)
> +{
> +	struct virtio_device *vdev = dev_to_virtio(dev);
> +
> +	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 3ca2edb1aef3..ce89126becc5 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>
>  
>  /**
>   * struct virtqueue - a queue to register buffers for sending or receiving.
> @@ -218,4 +219,12 @@ 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_page(struct device *dev, struct page *page, size_t offset,
> +			       unsigned int length, enum dma_data_direction dir);
> +dma_addr_t virtio_dma_map(struct device *dev, void *addr, unsigned int length,
> +			  enum dma_data_direction dir);
> +int virtio_dma_mapping_error(struct device *dev, dma_addr_t addr);
> +void virtio_dma_unmap(struct device *dev, dma_addr_t dma, unsigned int length,
> +		      enum dma_data_direction dir);
>  #endif /* _LINUX_VIRTIO_H */
> -- 
> 2.32.0.3.g01195cf9f