Re: [PATCH v2 4/7] media: vb2-dma-contig: add helper for setting dma max seg size

[Marek Szyprowski <m.szyprowski@samsung.com>]

Hello,

On 2015-12-13 20:57, Laurent Pinchart wrote:
> Hi Marek,
>
> Thank you for the patch.
>
> On Wednesday 09 December 2015 14:58:19 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>
>> ---
>>   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 c331272..628518d
>> 100644
>> --- a/drivers/media/v4l2-core/videobuf2-dma-contig.c
>> +++ b/drivers/media/v4l2-core/videobuf2-dma-contig.c
>> @@ -742,6 +742,21 @@ 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) {
> When can this function be called with dev->dma_parms not NULL ?

When one loads a module with multimedia driver (which calls this 
function), then
unloads and loads it again. It is rather safe to have this check.

>> +		dev->dma_parms = devm_kzalloc(dev, sizeof(dev->dma_parms),
>> +					      GFP_KERNEL);
>> +		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);
>> +
>>   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 c33dfa6..0e6ba64 100644
>> --- a/include/media/videobuf2-dma-contig.h
>> +++ b/include/media/videobuf2-dma-contig.h
>> @@ -26,6 +26,7 @@ vb2_dma_contig_plane_dma_addr(struct vb2_buffer *vb,
>> unsigned int plane_no)
>>
>>   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;

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland