Re: [Xen-devel] [PATCH 4/8] xen/gntdev: Allow mappings for DMA buffers

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 05/25/2018 11:33 AM, Oleksandr Andrushchenko wrote:
>  
>  struct unmap_notify {
> @@ -96,10 +104,28 @@ struct grant_map {
>       struct gnttab_unmap_grant_ref *kunmap_ops;
>       struct page **pages;
>       unsigned long pages_vm_start;
> +
> +#ifdef CONFIG_XEN_GRANT_DMA_ALLOC
> +     /*
> +      * If dmabuf_vaddr is not NULL then this mapping is backed by DMA
> +      * capable memory.
> +      */
> +
> +     /* Device for which DMA memory is allocated. */
> +     struct device *dma_dev;
> +     /* Flags used to create this DMA buffer: GNTDEV_DMABUF_FLAG_XXX. */
> +     bool dma_flags;

Again, I think most of the comments here can be dropped. Except possibly
for the flags.

> +     /* Virtual/CPU address of the DMA buffer. */
> +     void *dma_vaddr;
> +     /* Bus address of the DMA buffer. */
> +     dma_addr_t dma_bus_addr;
> +#endif
>  };
>  
>  static int unmap_grant_pages(struct grant_map *map, int offset, int pages);
>  
> +static struct miscdevice gntdev_miscdev;
> +
>  /* ------------------------------------------------------------------ */
>  
>  static void gntdev_print_maps(struct gntdev_priv *priv,
> @@ -121,8 +147,26 @@ static void gntdev_free_map(struct grant_map *map)
>       if (map == NULL)
>               return;
>  
> +#ifdef CONFIG_XEN_GRANT_DMA_ALLOC
> +     if (map->dma_vaddr) {
> +             struct gnttab_dma_alloc_args args;
> +
> +             args.dev = map->dma_dev;
> +             args.coherent = map->dma_flags & GNTDEV_DMA_FLAG_COHERENT;
> +             args.nr_pages = map->count;
> +             args.pages = map->pages;
> +             args.vaddr = map->dma_vaddr;
> +             args.dev_bus_addr = map->dma_bus_addr;
> +
> +             gnttab_dma_free_pages(&args);
> +     } else if (map->pages) {
> +             gnttab_free_pages(map->count, map->pages);
> +     }
> +#else
>       if (map->pages)
>               gnttab_free_pages(map->count, map->pages);
> +#endif
> +

} else
#endif
    if (map->pages)
        gnttab_free_pages(map->count, map->pages);


(and elsewhere)

>       kfree(map->pages);
>       kfree(map->grants);
>       kfree(map->map_ops);



>  
> diff --git a/include/uapi/xen/gntdev.h b/include/uapi/xen/gntdev.h
> index 6d1163456c03..2d5a4672f07c 100644
> --- a/include/uapi/xen/gntdev.h
> +++ b/include/uapi/xen/gntdev.h
> @@ -200,4 +200,19 @@ struct ioctl_gntdev_grant_copy {
>  /* Send an interrupt on the indicated event channel */
>  #define UNMAP_NOTIFY_SEND_EVENT 0x2
>  
> +/*
> + * Flags to be used while requesting memory mapping's backing storage
> + * to be allocated with DMA API.
> + */
> +
> +/*
> + * The buffer is backed with memory allocated with dma_alloc_wc.
> + */
> +#define GNTDEV_DMA_FLAG_WC           (1 << 1)


Is there a reason you are not using bit 0?

-boris

> +
> +/*
> + * The buffer is backed with memory allocated with dma_alloc_coherent.
> + */
> +#define GNTDEV_DMA_FLAG_COHERENT     (1 << 2)
> +
>  #endif /* __LINUX_PUBLIC_GNTDEV_H__ */


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