Re: [PATCHv5 08/13] v4l: vb2-dma-contig: add support for scatterlist in userptr mode

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Subash,

On Monday 07 May 2012 20:08:25 Subash Patel wrote:
> Hello Thomasz, Laurent,
> 
> I found an issue in the function vb2_dc_pages_to_sgt() below. I saw that
> during the attach, the size of the SGT and size requested mis-matched
> (by atleast 8k bytes). Hence I made a small correction to the code as
> below. I could then attach the importer properly.

Thank you for the report.

Could you print the content of the sglist (number of chunks and size of each 
chunk) before and after your modifications, as well as the values of n_pages, 
offset and size ?

> On 04/20/2012 08:15 PM, Tomasz Stanislawski wrote:

[snip]

> > +static struct sg_table *vb2_dc_pages_to_sgt(struct page **pages,
> > +	unsigned int n_pages, unsigned long offset, unsigned long size)
> > +{
> > +	struct sg_table *sgt;
> > +	unsigned int chunks;
> > +	unsigned int i;
> > +	unsigned int cur_page;
> > +	int ret;
> > +	struct scatterlist *s;
> > +
> > +	sgt = kzalloc(sizeof *sgt, GFP_KERNEL);
> > +	if (!sgt)
> > +		return ERR_PTR(-ENOMEM);
> > +
> > +	/* compute number of chunks */
> > +	chunks = 1;
> > +	for (i = 1; i<  n_pages; ++i)
> > +		if (pages[i] != pages[i - 1] + 1)
> > +			++chunks;
> > +
> > +	ret = sg_alloc_table(sgt, chunks, GFP_KERNEL);
> > +	if (ret) {
> > +		kfree(sgt);
> > +		return ERR_PTR(-ENOMEM);
> > +	}
> > +
> > +	/* merging chunks and putting them into the scatterlist */
> > +	cur_page = 0;
> > +	for_each_sg(sgt->sgl, s, sgt->orig_nents, i) {
> > +		unsigned long chunk_size;
> > +		unsigned int j;
> 
> 		size = PAGE_SIZE;
> 
> > +
> > +		for (j = cur_page + 1; j<  n_pages; ++j)
> 
> 		for (j = cur_page + 1; j < n_pages; ++j) {
> 
> > +			if (pages[j] != pages[j - 1] + 1)
> > +				break;
> 
> 			size += PAGE
> 		}
> 
> > +
> > +		chunk_size = ((j - cur_page)<<  PAGE_SHIFT) - offset;
> > +		sg_set_page(s, pages[cur_page], min(size, chunk_size), offset);
> 
> 		[DELETE] size -= chunk_size;
> 
> > +		offset = 0;
> > +		cur_page = j;
> > +	}
> > +
> > +	return sgt;
> > +}

-- 
Regards,

Laurent Pinchart