linux-kernel - Re: [PATCH v2] lib/scatterlist: Provide a DMA page iterator

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Date:   Fri, 8 Feb 2019 16:38:19 +0000
From:   Jason Gunthorpe <jgg@...lanox.com>
To:     Daniel Stone <daniel@...ishbar.org>, "hch@....de" <hch@....de>,
        "Koenig, Christian" <Christian.Koenig@....com>,
        Thomas Hellstrom <thellstrom@...are.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "yong.zhi@...el.com" <yong.zhi@...el.com>,
        "daniel.vetter@...ll.ch" <daniel.vetter@...ll.ch>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        "linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
        "bingbu.cao@...el.com" <bingbu.cao@...el.com>,
        "tian.shu.qiu@...el.com" <tian.shu.qiu@...el.com>,
        "shiraz.saleem@...el.com" <shiraz.saleem@...el.com>,
        "sakari.ailus@...ux.intel.com" <sakari.ailus@...ux.intel.com>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>
Subject: Re: [PATCH v2] lib/scatterlist: Provide a DMA page iterator

On Thu, Feb 07, 2019 at 03:26:47PM -0700, Jason Gunthorpe wrote:
> diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_ttm_buffer.c b/drivers/gpu/drm/vmwgfx/vmwgfx_ttm_buffer.c
> index 31786b200afc47..e84f6aaee778f0 100644
> +++ b/drivers/gpu/drm/vmwgfx/vmwgfx_ttm_buffer.c
> @@ -311,7 +311,13 @@ static dma_addr_t __vmw_piter_dma_addr(struct vmw_piter *viter)
>  
>  static dma_addr_t __vmw_piter_sg_addr(struct vmw_piter *viter)
>  {
> -	return sg_page_iter_dma_address(&viter->iter);
> +	/*
> +	 * FIXME: This driver wrongly mixes DMA and CPU SG list iteration and
> +	 * needs revision. See
> +	 * https://lore.kernel.org/lkml/20190104223531.GA1705@ziepe.ca/
> +	 */
> +	return sg_page_iter_dma_address(
> +		(struct sg_dma_page_iter *)&viter->iter);

Occured to me this would be better written as:

	return sg_page_iter_dma_address(
		container_of(&viter->iter, struct sg_dma_page_iter, base));

Since I think we are done with this now I'll fix it when I apply this
patch

Thanks for all the acks everyone

Regards,
Jason