Re: [PATCH RESEND 1/2] media: vb2-dma-contig: add helper for setting dma max seg size

[Hans Verkuil <hverkuil@xs4all.nl>]

On 04/27/2016 02:00 PM, Marek Szyprowski wrote:
> Add a helper function for device drivers to set DMA's max_seg_size.
> Setting it to largest possible value lets DMA-mapping API always create
> contiguous mappings in DMA address space. This is essential for all
> devices, which use dma-contig videobuf2 memory allocator and shared
> buffers.
> 
> Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
> ---
> This patch was posted earlier as a part of
> http://thread.gmane.org/gmane.linux.drivers.video-input-infrastructure/97316
> thread, but applying it is really needed to get all Exynos multimedia
> drivers working with IOMMU enabled.
> 
> Best regards,
> Marek Szyprowski
> ---
>  drivers/media/v4l2-core/videobuf2-dma-contig.c | 15 +++++++++++++++
>  include/media/videobuf2-dma-contig.h           |  1 +
>  2 files changed, 16 insertions(+)
> 
> diff --git a/drivers/media/v4l2-core/videobuf2-dma-contig.c b/drivers/media/v4l2-core/videobuf2-dma-contig.c
> index 5361197..f611456 100644
> --- a/drivers/media/v4l2-core/videobuf2-dma-contig.c
> +++ b/drivers/media/v4l2-core/videobuf2-dma-contig.c
> @@ -753,6 +753,21 @@ void vb2_dma_contig_cleanup_ctx(void *alloc_ctx)
>  }
>  EXPORT_SYMBOL_GPL(vb2_dma_contig_cleanup_ctx);
>  
> +int vb2_dma_contig_set_max_seg_size(struct device *dev, unsigned int size)
> +{
> +	if (!dev->dma_parms) {
> +		dev->dma_parms = devm_kzalloc(dev, sizeof(dev->dma_parms),
> +					      GFP_KERNEL);

The v3 patch from December uses kzalloc here. Is this perhaps on old version?

> +		if (!dev->dma_parms)
> +			return -ENOMEM;
> +	}
> +	if (dma_get_max_seg_size(dev) < size)
> +		return dma_set_max_seg_size(dev, size);
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(vb2_dma_contig_set_max_seg_size);

Admittedly I haven't looked closely at this, but is this something that you
want for all dma-contig devices? Or to rephrase this question: what type of
devices will need this?

Regards,

	Hans

> +
>  MODULE_DESCRIPTION("DMA-contig memory handling routines for videobuf2");
>  MODULE_AUTHOR("Pawel Osciak <pawel@osciak.com>");
>  MODULE_LICENSE("GPL");
> diff --git a/include/media/videobuf2-dma-contig.h b/include/media/videobuf2-dma-contig.h
> index 2087c9a..98857b5 100644
> --- a/include/media/videobuf2-dma-contig.h
> +++ b/include/media/videobuf2-dma-contig.h
> @@ -35,6 +35,7 @@ static inline void *vb2_dma_contig_init_ctx(struct device *dev)
>  }
>  
>  void vb2_dma_contig_cleanup_ctx(void *alloc_ctx);
> +int vb2_dma_contig_set_max_seg_size(struct device *dev, unsigned int size);
>  
>  extern const struct vb2_mem_ops vb2_dma_contig_memops;
>  
>