Subject: Re: [PATCH 08/33] virtio_ring: introduce dma sync api for virtio

From: "Michael S. Tsirkin" <[email-masked]>
Date: Fri, 3 Feb 2023 04:24:30 -0500

On Thu, Feb 02, 2023 at 07:00:33PM +0800, Xuan Zhuo wrote:
> In the process of dma sync, we involved whether virtio uses dma api. On
> the other hand, it is also necessary to read vdev->dev.parent. So these
> API has been introduced.

you don't need to repeat implementation here.
just list the new APIs and how they will be used
with premapped API.

> Signed-off-by: Xuan Zhuo <[email-masked]>
> ---
>  drivers/virtio/virtio_ring.c | 61 ++++++++++++++++++++++++++++++++++++
>  include/linux/virtio.h       |  8 +++++
>  2 files changed, 69 insertions(+)
> 
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index 67eda7bc23ea..7b393133fd27 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -3102,4 +3102,65 @@ void virtio_dma_unmap(struct device *dev, dma_addr_t dma, unsigned int length,
>  }
>  EXPORT_SYMBOL_GPL(virtio_dma_unmap);
>  
> +/**
> + * virtio_dma_need_sync - check dma address need sync

.... whether a dma address needs sync

> + * @dev: virtio device
> + * @addr: DMA address
> + */
> +bool virtio_dma_need_sync(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_need_sync(vdev->dev.parent, addr);
> +}
> +EXPORT_SYMBOL_GPL(virtio_dma_need_sync);
> +
> +/**
> + * virtio_dma_sync_signle_range_for_cpu - dma sync for cpu
> + * @dev: virtio device
> + * @addr: DMA address
> + * @offset: DMA address offset
> + * @size: mem size for sync
> + * @dir: DMA direction
> + *
> + * Before calling this function, use virtio_dma_need_sync() to confirm that the
> + * DMA address really needs to be synchronized
> + */
> +void virtio_dma_sync_signle_range_for_cpu(struct device *dev, dma_addr_t addr,
> +					  unsigned long offset, size_t size,
> +					  enum dma_data_direction dir)
> +{
> +	struct virtio_device *vdev = dev_to_virtio(dev);
> +
> +	dma_sync_single_range_for_cpu(vdev->dev.parent, addr, offset,
> +				      size, DMA_BIDIRECTIONAL);
> +}
> +EXPORT_SYMBOL_GPL(virtio_dma_sync_signle_range_for_cpu);
> +
> +/**
> + * virtio_dma_sync_signle_range_for_device - dma sync for device
> + * @dev: virtio device
> + * @addr: DMA address
> + * @offset: DMA address offset
> + * @size: mem size for sync
> + * @dir: DMA direction
> + *
> + * Before calling this function, use virtio_dma_need_sync() to confirm that the
> + * DMA address really needs to be synchronized
> + */
> +void virtio_dma_sync_signle_range_for_device(struct device *dev,
> +					     dma_addr_t addr,
> +					     unsigned long offset, size_t size,
> +					     enum dma_data_direction dir)
> +{
> +	struct virtio_device *vdev = dev_to_virtio(dev);
> +
> +	dma_sync_single_range_for_device(vdev->dev.parent, addr, offset,
> +					 size, DMA_BIDIRECTIONAL);
> +}
> +EXPORT_SYMBOL_GPL(virtio_dma_sync_signle_range_for_device);
> +

Pls document how these APIs are only for pre-mapped buffers,
for non premapped virtio core handles DMA API internally.

>  MODULE_LICENSE("GPL");
> diff --git a/include/linux/virtio.h b/include/linux/virtio.h
> index ce89126becc5..8c2fae318b0c 100644
> --- a/include/linux/virtio.h
> +++ b/include/linux/virtio.h
> @@ -227,4 +227,12 @@ dma_addr_t virtio_dma_map(struct device *dev, void *addr, unsigned int length,
>  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);
> +bool virtio_dma_need_sync(struct device *dev, dma_addr_t addr);
> +void virtio_dma_sync_signle_range_for_cpu(struct device *dev, dma_addr_t addr,
> +					  unsigned long offset, size_t size,
> +					  enum dma_data_direction dir);
> +void virtio_dma_sync_signle_range_for_device(struct device *dev,
> +					     dma_addr_t addr,
> +					     unsigned long offset, size_t size,
> +					     enum dma_data_direction dir);
>  #endif /* _LINUX_VIRTIO_H */
> -- 
> 2.32.0.3.g01195cf9f