lkml.org 
[lkml]   [2020]   [Jun]   [19]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH v7 33/36] rapidio: fix common struct sg_table related issues
Date
The Documentation/DMA-API-HOWTO.txt states that the dma_map_sg() function
returns the number of the created entries in the DMA address space.
However the subsequent calls to the dma_sync_sg_for_{device,cpu}() and
dma_unmap_sg must be called with the original number of the entries
passed to the dma_map_sg().

struct sg_table is a common structure used for describing a non-contiguous
memory buffer, used commonly in the DRM and graphics subsystems. It
consists of a scatterlist with memory pages and DMA addresses (sgl entry),
as well as the number of scatterlist entries: CPU pages (orig_nents entry)
and DMA mapped pages (nents entry).

It turned out that it was a common mistake to misuse nents and orig_nents
entries, calling DMA-mapping functions with a wrong number of entries or
ignoring the number of mapped entries returned by the dma_map_sg()
function.

To avoid such issues, lets use a common dma-mapping wrappers operating
directly on the struct sg_table objects and use scatterlist page
iterators where possible. This, almost always, hides references to the
nents and orig_nents entries, making the code robust, easier to follow
and copy/paste safe.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
---
drivers/rapidio/devices/rio_mport_cdev.c | 8 +++-----
1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/drivers/rapidio/devices/rio_mport_cdev.c b/drivers/rapidio/devices/rio_mport_cdev.c
index 451608e960a1..98c572627c8c 100644
--- a/drivers/rapidio/devices/rio_mport_cdev.c
+++ b/drivers/rapidio/devices/rio_mport_cdev.c
@@ -573,8 +573,7 @@ static void dma_req_free(struct kref *ref)
refcount);
struct mport_cdev_priv *priv = req->priv;

- dma_unmap_sg(req->dmach->device->dev,
- req->sgt.sgl, req->sgt.nents, req->dir);
+ dma_unmap_sgtable(req->dmach->device->dev, &req->sgt, req->dir, 0);
sg_free_table(&req->sgt);
if (req->page_list) {
unpin_user_pages(req->page_list, req->nr_pages);
@@ -930,9 +929,8 @@ rio_dma_transfer(struct file *filp, u32 transfer_mode,
xfer->offset, xfer->length);
}

- nents = dma_map_sg(chan->device->dev,
- req->sgt.sgl, req->sgt.nents, dir);
- if (nents == 0) {
+ ret = dma_map_sgtable(chan->device->dev, &req->sgt, dir, 0);
+ if (ret) {
rmcd_error("Failed to map SG list");
ret = -EFAULT;
goto err_pg;
--
2.17.1
\
 
 \ /
  Last update: 2020-06-19 12:46    [W:0.651 / U:0.216 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site