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

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Message-ID: <9f2999a8-7786-5811-bdf0-ff7f30301cf2@oracle.com>
Date:   Tue, 29 May 2018 17:52:14 -0400
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Oleksandr Andrushchenko <andr2000@...il.com>,
        xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, linux-media@...r.kernel.org,
        jgross@...e.com, konrad.wilk@...cle.com
Cc:     daniel.vetter@...el.com, dongwon.kim@...el.com,
        matthew.d.roper@...el.com,
        Oleksandr Andrushchenko <oleksandr_andrushchenko@...m.com>
Subject: Re: [PATCH 4/8] xen/gntdev: Allow mappings for DMA buffers

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__ */