linux-kernel - Re: [PATCH 4/4] staging: android: ion: Support for mapping with dma mapping attributes

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Date:   Mon, 21 Jan 2019 12:19:08 +0000
From:   Brian Starkey <Brian.Starkey@....com>
To:     Liam Mark <lmark@...eaurora.org>
CC:     "labbott@...hat.com" <labbott@...hat.com>,
        "sumit.semwal@...aro.org" <sumit.semwal@...aro.org>,
        "devel@...verdev.osuosl.org" <devel@...verdev.osuosl.org>,
        "tkjos@...roid.com" <tkjos@...roid.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "afd@...com" <afd@...com>,
        "linaro-mm-sig@...ts.linaro.org" <linaro-mm-sig@...ts.linaro.org>,
        "arve@...roid.com" <arve@...roid.com>,
        "joel@...lfernandes.org" <joel@...lfernandes.org>,
        "maco@...roid.com" <maco@...roid.com>,
        "christian@...uner.io" <christian@...uner.io>, nd <nd@....com>
Subject: Re: [PATCH 4/4] staging: android: ion: Support for mapping with dma
 mapping attributes

Hi Liam,

On Fri, Jan 18, 2019 at 10:37:47AM -0800, Liam Mark wrote:
> Add support for configuring dma mapping attributes when mapping
> and unmapping memory through dma_buf_map_attachment and
> dma_buf_unmap_attachment.
> 
> For example this will allow ION clients to skip cache maintenance, by
> using DMA_ATTR_SKIP_CPU_SYNC, for buffers which are clean and haven't been
> accessed by the CPU.

How can a client know that the buffer won't be accessed by the CPU in
the future though?

I don't think we can push this decision to clients, because they are
lacking information about what else is going on with the buffer. It
needs to be done by the exporter, IMO.

Thanks,
-Brian

> 
> Signed-off-by: Liam Mark <lmark@...eaurora.org>
> ---
>  drivers/staging/android/ion/ion.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/staging/android/ion/ion.c b/drivers/staging/android/ion/ion.c
> index 1fe633a7fdba..0aae845b20ba 100644
> --- a/drivers/staging/android/ion/ion.c
> +++ b/drivers/staging/android/ion/ion.c
> @@ -268,8 +268,8 @@ static struct sg_table *ion_map_dma_buf(struct dma_buf_attachment *attachment,
>  	table = a->table;
>  
>  	mutex_lock(&buffer->lock);
> -	if (!dma_map_sg(attachment->dev, table->sgl, table->nents,
> -			direction)) {
> +	if (!dma_map_sg_attrs(attachment->dev, table->sgl, table->nents,
> +			      direction, attachment->dma_map_attrs)) {
>  		mutex_unlock(&buffer->lock);
>  		return ERR_PTR(-ENOMEM);
>  	}
> @@ -287,7 +287,8 @@ static void ion_unmap_dma_buf(struct dma_buf_attachment *attachment,
>  	struct ion_buffer *buffer = attachment->dmabuf->priv;
>  
>  	mutex_lock(&buffer->lock);
> -	dma_unmap_sg(attachment->dev, table->sgl, table->nents, direction);
> +	dma_unmap_sg_attrs(attachment->dev, table->sgl, table->nents, direction,
> +			   attachment->dma_map_attrs);
>  	a->dma_mapped = false;
>  	mutex_unlock(&buffer->lock);
>  }
> -- 
> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, 
> a Linux Foundation Collaborative Project
> 
> _______________________________________________
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> dri-devel@...ts.freedesktop.org
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