linux-kernel - [PATCH] [TEST]: media: vb2: reverse DMA addr of each plane

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Date:   Fri,  8 Mar 2019 18:04:40 +0800
From:   Randy Li <randy.li@...k-chips.com>
To:     linux-media@...r.kernel.org
Cc:     Randy Li <randy.li@...k-chips.com>, ayaka@...lik.info,
        joro@...tes.org, iommu@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, pawel@...iak.com,
        m.szyprowski@...sung.com, kyungmin.park@...sung.com,
        mchehab@...nel.org, hverkuil@...all.nl, nicolas@...fresne.ca,
        ezequiel@...labora.com, posciak@...omium.org, groeck@...omium.org,
        paul.kocialkowski@...tlin.com, linux-rockchip@...ts.infradead.org
Subject: [PATCH] [TEST]: media: vb2: reverse DMA addr of each plane

With the default iova and dma-iommu driver, the starting
address of a new buffer would be at lower address than
the previous one.

This patch can solve this problem simply, but I want
a way to control the address direction of the IOMMU/IOVA.

The reason why we(ayaka and I) need to do this is simple,
some devices want a contiguous memory for its pixel data.
But with the single plane buffer, there is not a properly way
to export its buffer offsets with the userspace,
since their bytesperline and offset are not full related
to the picture width or height. You can find more detail
in the previous mail.

Besides, this patch won't solve all the problem, if you
don't disable the size_aligned of the iova driver or
there would be a gap between the plane 0 and plane 1.

This patch is used for showing the problem we met not
for merging.

Signed-off-by: Randy Li <randy.li@...k-chips.com>
---
 drivers/media/common/videobuf2/videobuf2-core.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/drivers/media/common/videobuf2/videobuf2-core.c b/drivers/media/common/videobuf2/videobuf2-core.c
index 15b6b9c0a2e4..6762d1547e49 100644
--- a/drivers/media/common/videobuf2/videobuf2-core.c
+++ b/drivers/media/common/videobuf2/videobuf2-core.c
@@ -204,11 +204,11 @@ static int __vb2_buf_mem_alloc(struct vb2_buffer *vb)
 	 * Allocate memory for all planes in this buffer
 	 * NOTE: mmapped areas should be page aligned
 	 */
-	for (plane = 0; plane < vb->num_planes; ++plane) {
-		unsigned long size = PAGE_ALIGN(vb->planes[plane].length);
+	for (plane = vb->num_planes; plane > 0; --plane) {
+		unsigned long size = PAGE_ALIGN(vb->planes[plane - 1].length);
 
 		mem_priv = call_ptr_memop(vb, alloc,
-				q->alloc_devs[plane] ? : q->dev,
+				q->alloc_devs[plane - 1] ? : q->dev,
 				q->dma_attrs, size, q->dma_dir, q->gfp_flags);
 		if (IS_ERR_OR_NULL(mem_priv)) {
 			if (mem_priv)
@@ -217,15 +217,15 @@ static int __vb2_buf_mem_alloc(struct vb2_buffer *vb)
 		}
 
 		/* Associate allocator private data with this plane */
-		vb->planes[plane].mem_priv = mem_priv;
+		vb->planes[plane - 1].mem_priv = mem_priv;
 	}
 
 	return 0;
 free:
 	/* Free already allocated memory if one of the allocations failed */
-	for (; plane > 0; --plane) {
-		call_void_memop(vb, put, vb->planes[plane - 1].mem_priv);
-		vb->planes[plane - 1].mem_priv = NULL;
+	for (; plane < vb->num_planes; plane++) {
+		call_void_memop(vb, put, vb->planes[plane].mem_priv);
+		vb->planes[plane].mem_priv = NULL;
 	}
 
 	return ret;
-- 
2.20.1