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

[Oleksandr Andrushchenko]

On 05/30/2018 12:52 AM, Boris Ostrovsky wrote:
> 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.
will drop most of those
> > +	/* 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
>  ÂÂÂ if (map->pages)
>  ÂÂÂ ÂÂÂ gnttab_free_pages(map->count, map->pages);
>
>
> (and elsewhere)
ok, just wasn't sure if it is ok to violate kernel coding style here ;)
> >   	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?
No reason for that, will start from 0
> -boris
Thank you,
Oleksandr
> > +
> > +/*
> > + * The buffer is backed with memory allocated with dma_alloc_coherent.
> > + */
> > +#define GNTDEV_DMA_FLAG_COHERENT	(1 << 2)
> > +
> >   #endif /* __LINUX_PUBLIC_GNTDEV_H__ */