linux-kernel - RE: [PATCH 1/2] device: add dma_params->max_segment

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Message-id: <018b01cd663f$d3a23c10$7ae6b430$%szyprowski@samsung.com>
Date:	Fri, 20 Jul 2012 08:20:50 +0200
From:	Marek Szyprowski <m.szyprowski@...sung.com>
To:	'Rob Clark' <rob.clark@...aro.org>, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-mm@...ck.org,
	linaro-mm-sig@...ts.linaro.org, dri-devel@...ts.freedesktop.org,
	linux-media@...r.kernel.org
Cc:	patches@...aro.org, linux@....linux.org.uk, arnd@...db.de,
	jesse.barker@...aro.org, daniel@...ll.ch,
	Tomasz Stanislawski <t.stanislaws@...sung.com>,
	sumit.semwal@...com, maarten.lankhorst@...onical.com,
	'Rob Clark' <rob@...com>
Subject: RE: [PATCH 1/2] device: add dma_params->max_segment_count

Hello,

On Thursday, July 19, 2012 6:24 PM Rob Clark wrote:

> From: Rob Clark <rob@...com>
> 
> For devices which have constraints about maximum number of segments
> in an sglist.  For example, a device which could only deal with
> contiguous buffers would set max_segment_count to 1.
> 
> The initial motivation is for devices sharing buffers via dma-buf,
> to allow the buffer exporter to know the constraints of other
> devices which have attached to the buffer.  The dma_mask and fields
> in 'struct device_dma_parameters' tell the exporter everything else
> that is needed, except whether the importer has constraints about
> maximum number of segments.
> 
> Signed-off-by: Rob Clark <rob@...com>

Yea, it is a really good idea to add this to struct device_dma_parameters.
We only need to initialize it to '1' in platform startup code for all 
devices relevant to buffer sharing.

Acked-by: Marek Szyprowski <m.szyprowski@...sung.com>

> ---
>  include/linux/device.h      |    1 +
>  include/linux/dma-mapping.h |   16 ++++++++++++++++
>  2 files changed, 17 insertions(+)
> 
> diff --git a/include/linux/device.h b/include/linux/device.h
> index 161d962..3813735 100644
> --- a/include/linux/device.h
> +++ b/include/linux/device.h
> @@ -568,6 +568,7 @@ struct device_dma_parameters {
>  	 * sg limitations.
>  	 */
>  	unsigned int max_segment_size;
> +	unsigned int max_segment_count;    /* zero for unlimited */
>  	unsigned long segment_boundary_mask;
>  };
> 
> diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
> index dfc099e..f380f79 100644
> --- a/include/linux/dma-mapping.h
> +++ b/include/linux/dma-mapping.h
> @@ -111,6 +111,22 @@ static inline unsigned int dma_set_max_seg_size(struct device *dev,
>  		return -EIO;
>  }
> 
> +static inline unsigned int dma_get_max_seg_count(struct device *dev)
> +{
> +	return dev->dma_parms ? dev->dma_parms->max_segment_count : 0;
> +}
> +
> +static inline int dma_set_max_seg_count(struct device *dev,
> +						unsigned int count)
> +{
> +	if (dev->dma_parms) {
> +		dev->dma_parms->max_segment_count = count;
> +		return 0;
> +	} else
> +		return -EIO;
> +}
> +
> +
>  static inline unsigned long dma_get_seg_boundary(struct device *dev)
>  {
>  	return dev->dma_parms ?
> --
> 1.7.9.5

Best regards
-- 
Marek Szyprowski
Samsung Poland R&D Center



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