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Subject[PATCH v7 3/6] dmaengine: xilinx_dma: Fix race condition in the driver for multiple descriptor scenario
Date
As per axi dmaengine spec the software must not move the tail pointer
to a location that has not been updated (next descriptor field of the
h/w descriptor should always point to a valid address).

When user submits multiple descriptors on the recv side, with the
current driver flow the last buffer descriptor next descriptor field
points to a invalid location, resulting the invalid data or errors from the
axidma dmaengine.

This patch fixes this issue by creating a buffer descritpor chain during
channel allocation itself and use those buffer descriptors for the
subsequent dma operations.

Signed-off-by: Kedareswara rao Appana <appanad@xilinx.com>
---
Changes for v7:
---> None.
Changes for v6:
---> Updated Commit message as suggested by Vinod.
Changes for v5:
---> None.
Changes for v4:
---> None.
Changes for v3:
---> None.
Changes for v2:
---> None.

drivers/dma/xilinx/xilinx_dma.c | 135 +++++++++++++++++++++++++---------------
1 file changed, 84 insertions(+), 51 deletions(-)

diff --git a/drivers/dma/xilinx/xilinx_dma.c b/drivers/dma/xilinx/xilinx_dma.c
index 9063ca0..ab01306 100644
--- a/drivers/dma/xilinx/xilinx_dma.c
+++ b/drivers/dma/xilinx/xilinx_dma.c
@@ -165,6 +165,7 @@
#define XILINX_DMA_BD_SOP BIT(27)
#define XILINX_DMA_BD_EOP BIT(26)
#define XILINX_DMA_COALESCE_MAX 255
+#define XILINX_DMA_NUM_DESCS 255
#define XILINX_DMA_NUM_APP_WORDS 5

/* Multi-Channel DMA Descriptor offsets*/
@@ -312,6 +313,7 @@ struct xilinx_dma_tx_descriptor {
* @pending_list: Descriptors waiting
* @active_list: Descriptors ready to submit
* @done_list: Complete descriptors
+ * @free_seg_list: Free descriptors
* @common: DMA common channel
* @desc_pool: Descriptors pool
* @dev: The dma device
@@ -332,7 +334,9 @@ struct xilinx_dma_tx_descriptor {
* @desc_submitcount: Descriptor h/w submitted count
* @residue: Residue for AXI DMA
* @seg_v: Statically allocated segments base
+ * @seg_p: Physical allocated segments base
* @cyclic_seg_v: Statically allocated segment base for cyclic transfers
+ * @cyclic_seg_p: Physical allocated segments base for cyclic dma
* @start_transfer: Differentiate b/w DMA IP's transfer
* @stop_transfer: Differentiate b/w DMA IP's quiesce
*/
@@ -344,6 +348,7 @@ struct xilinx_dma_chan {
struct list_head pending_list;
struct list_head active_list;
struct list_head done_list;
+ struct list_head free_seg_list;
struct dma_chan common;
struct dma_pool *desc_pool;
struct device *dev;
@@ -364,7 +369,9 @@ struct xilinx_dma_chan {
u32 desc_submitcount;
u32 residue;
struct xilinx_axidma_tx_segment *seg_v;
+ dma_addr_t seg_p;
struct xilinx_axidma_tx_segment *cyclic_seg_v;
+ dma_addr_t cyclic_seg_p;
void (*start_transfer)(struct xilinx_dma_chan *chan);
int (*stop_transfer)(struct xilinx_dma_chan *chan);
u16 tdest;
@@ -584,18 +591,32 @@ xilinx_cdma_alloc_tx_segment(struct xilinx_dma_chan *chan)
static struct xilinx_axidma_tx_segment *
xilinx_axidma_alloc_tx_segment(struct xilinx_dma_chan *chan)
{
- struct xilinx_axidma_tx_segment *segment;
- dma_addr_t phys;
-
- segment = dma_pool_zalloc(chan->desc_pool, GFP_ATOMIC, &phys);
- if (!segment)
- return NULL;
+ struct xilinx_axidma_tx_segment *segment = NULL;
+ unsigned long flags;

- segment->phys = phys;
+ spin_lock_irqsave(&chan->lock, flags);
+ if (!list_empty(&chan->free_seg_list)) {
+ segment = list_first_entry(&chan->free_seg_list,
+ struct xilinx_axidma_tx_segment,
+ node);
+ list_del(&segment->node);
+ }
+ spin_unlock_irqrestore(&chan->lock, flags);

return segment;
}

+static void xilinx_dma_clean_hw_desc(struct xilinx_axidma_desc_hw *hw)
+{
+ u32 next_desc = hw->next_desc;
+ u32 next_desc_msb = hw->next_desc_msb;
+
+ memset(hw, 0, sizeof(struct xilinx_axidma_desc_hw));
+
+ hw->next_desc = next_desc;
+ hw->next_desc_msb = next_desc_msb;
+}
+
/**
* xilinx_dma_free_tx_segment - Free transaction segment
* @chan: Driver specific DMA channel
@@ -604,7 +625,9 @@ xilinx_axidma_alloc_tx_segment(struct xilinx_dma_chan *chan)
static void xilinx_dma_free_tx_segment(struct xilinx_dma_chan *chan,
struct xilinx_axidma_tx_segment *segment)
{
- dma_pool_free(chan->desc_pool, segment, segment->phys);
+ xilinx_dma_clean_hw_desc(&segment->hw);
+
+ list_add_tail(&segment->node, &chan->free_seg_list);
}

/**
@@ -729,16 +752,26 @@ static void xilinx_dma_free_descriptors(struct xilinx_dma_chan *chan)
static void xilinx_dma_free_chan_resources(struct dma_chan *dchan)
{
struct xilinx_dma_chan *chan = to_xilinx_chan(dchan);
+ unsigned long flags;

dev_dbg(chan->dev, "Free all channel resources.\n");

xilinx_dma_free_descriptors(chan);
+
if (chan->xdev->dma_config->dmatype == XDMA_TYPE_AXIDMA) {
- xilinx_dma_free_tx_segment(chan, chan->cyclic_seg_v);
- xilinx_dma_free_tx_segment(chan, chan->seg_v);
+ spin_lock_irqsave(&chan->lock, flags);
+ INIT_LIST_HEAD(&chan->free_seg_list);
+ spin_unlock_irqrestore(&chan->lock, flags);
+
+ /* Free Memory that is allocated for cyclic DMA Mode */
+ dma_free_coherent(chan->dev, sizeof(*chan->cyclic_seg_v),
+ chan->cyclic_seg_v, chan->cyclic_seg_p);
+ }
+
+ if (chan->xdev->dma_config->dmatype != XDMA_TYPE_AXIDMA) {
+ dma_pool_destroy(chan->desc_pool);
+ chan->desc_pool = NULL;
}
- dma_pool_destroy(chan->desc_pool);
- chan->desc_pool = NULL;
}

/**
@@ -821,6 +854,7 @@ static void xilinx_dma_do_tasklet(unsigned long data)
static int xilinx_dma_alloc_chan_resources(struct dma_chan *dchan)
{
struct xilinx_dma_chan *chan = to_xilinx_chan(dchan);
+ int i;

/* Has this channel already been allocated? */
if (chan->desc_pool)
@@ -831,11 +865,30 @@ static int xilinx_dma_alloc_chan_resources(struct dma_chan *dchan)
* for meeting Xilinx VDMA specification requirement.
*/
if (chan->xdev->dma_config->dmatype == XDMA_TYPE_AXIDMA) {
- chan->desc_pool = dma_pool_create("xilinx_dma_desc_pool",
- chan->dev,
- sizeof(struct xilinx_axidma_tx_segment),
- __alignof__(struct xilinx_axidma_tx_segment),
- 0);
+ /* Allocate the buffer descriptors. */
+ chan->seg_v = dma_zalloc_coherent(chan->dev,
+ sizeof(*chan->seg_v) *
+ XILINX_DMA_NUM_DESCS,
+ &chan->seg_p, GFP_KERNEL);
+ if (!chan->seg_v) {
+ dev_err(chan->dev,
+ "unable to allocate channel %d descriptors\n",
+ chan->id);
+ return -ENOMEM;
+ }
+
+ for (i = 0; i < XILINX_DMA_NUM_DESCS; i++) {
+ chan->seg_v[i].hw.next_desc =
+ lower_32_bits(chan->seg_p + sizeof(*chan->seg_v) *
+ ((i + 1) % XILINX_DMA_NUM_DESCS));
+ chan->seg_v[i].hw.next_desc_msb =
+ upper_32_bits(chan->seg_p + sizeof(*chan->seg_v) *
+ ((i + 1) % XILINX_DMA_NUM_DESCS));
+ chan->seg_v[i].phys = chan->seg_p +
+ sizeof(*chan->seg_v) * i;
+ list_add_tail(&chan->seg_v[i].node,
+ &chan->free_seg_list);
+ }
} else if (chan->xdev->dma_config->dmatype == XDMA_TYPE_CDMA) {
chan->desc_pool = dma_pool_create("xilinx_cdma_desc_pool",
chan->dev,
@@ -850,7 +903,8 @@ static int xilinx_dma_alloc_chan_resources(struct dma_chan *dchan)
0);
}

- if (!chan->desc_pool) {
+ if (!chan->desc_pool &&
+ (chan->xdev->dma_config->dmatype != XDMA_TYPE_AXIDMA)) {
dev_err(chan->dev,
"unable to allocate channel %d descriptor pool\n",
chan->id);
@@ -859,22 +913,20 @@ static int xilinx_dma_alloc_chan_resources(struct dma_chan *dchan)

if (chan->xdev->dma_config->dmatype == XDMA_TYPE_AXIDMA) {
/*
- * For AXI DMA case after submitting a pending_list, keep
- * an extra segment allocated so that the "next descriptor"
- * pointer on the tail descriptor always points to a
- * valid descriptor, even when paused after reaching taildesc.
- * This way, it is possible to issue additional
- * transfers without halting and restarting the channel.
- */
- chan->seg_v = xilinx_axidma_alloc_tx_segment(chan);
-
- /*
* For cyclic DMA mode we need to program the tail Descriptor
* register with a value which is not a part of the BD chain
* so allocating a desc segment during channel allocation for
* programming tail descriptor.
*/
- chan->cyclic_seg_v = xilinx_axidma_alloc_tx_segment(chan);
+ chan->cyclic_seg_v = dma_zalloc_coherent(chan->dev,
+ sizeof(*chan->cyclic_seg_v),
+ &chan->cyclic_seg_p, GFP_KERNEL);
+ if (!chan->cyclic_seg_v) {
+ dev_err(chan->dev,
+ "unable to allocate desc segment for cyclic DMA\n");
+ return -ENOMEM;
+ }
+ chan->cyclic_seg_v->phys = chan->cyclic_seg_p;
}

dma_cookie_init(dchan);
@@ -1184,7 +1236,7 @@ static void xilinx_cdma_start_transfer(struct xilinx_dma_chan *chan)
static void xilinx_dma_start_transfer(struct xilinx_dma_chan *chan)
{
struct xilinx_dma_tx_descriptor *head_desc, *tail_desc;
- struct xilinx_axidma_tx_segment *tail_segment, *old_head, *new_head;
+ struct xilinx_axidma_tx_segment *tail_segment;
u32 reg;

if (chan->err)
@@ -1203,21 +1255,6 @@ static void xilinx_dma_start_transfer(struct xilinx_dma_chan *chan)
tail_segment = list_last_entry(&tail_desc->segments,
struct xilinx_axidma_tx_segment, node);

- if (chan->has_sg && !chan->xdev->mcdma) {
- old_head = list_first_entry(&head_desc->segments,
- struct xilinx_axidma_tx_segment, node);
- new_head = chan->seg_v;
- /* Copy Buffer Descriptor fields. */
- new_head->hw = old_head->hw;
-
- /* Swap and save new reserve */
- list_replace_init(&old_head->node, &new_head->node);
- chan->seg_v = old_head;
-
- tail_segment->hw.next_desc = chan->seg_v->phys;
- head_desc->async_tx.phys = new_head->phys;
- }
-
reg = dma_ctrl_read(chan, XILINX_DMA_REG_DMACR);

if (chan->desc_pendingcount <= XILINX_DMA_COALESCE_MAX) {
@@ -1705,7 +1742,7 @@ static struct dma_async_tx_descriptor *xilinx_dma_prep_slave_sg(
{
struct xilinx_dma_chan *chan = to_xilinx_chan(dchan);
struct xilinx_dma_tx_descriptor *desc;
- struct xilinx_axidma_tx_segment *segment = NULL, *prev = NULL;
+ struct xilinx_axidma_tx_segment *segment = NULL;
u32 *app_w = (u32 *)context;
struct scatterlist *sg;
size_t copy;
@@ -1756,10 +1793,6 @@ static struct dma_async_tx_descriptor *xilinx_dma_prep_slave_sg(
XILINX_DMA_NUM_APP_WORDS);
}

- if (prev)
- prev->hw.next_desc = segment->phys;
-
- prev = segment;
sg_used += copy;

/*
@@ -1773,7 +1806,6 @@ static struct dma_async_tx_descriptor *xilinx_dma_prep_slave_sg(
segment = list_first_entry(&desc->segments,
struct xilinx_axidma_tx_segment, node);
desc->async_tx.phys = segment->phys;
- prev->hw.next_desc = segment->phys;

/* For the last DMA_MEM_TO_DEV transfer, set EOP */
if (chan->direction == DMA_MEM_TO_DEV) {
@@ -2328,6 +2360,7 @@ static int xilinx_dma_chan_probe(struct xilinx_dma_device *xdev,
INIT_LIST_HEAD(&chan->pending_list);
INIT_LIST_HEAD(&chan->done_list);
INIT_LIST_HEAD(&chan->active_list);
+ INIT_LIST_HEAD(&chan->free_seg_list);

/* Retrieve the channel properties from the device tree */
has_dre = of_property_read_bool(node, "xlnx,include-dre");
--
2.7.4
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