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Commit 23059408 authored by Kedareswara rao Appana's avatar Kedareswara rao Appana Committed by Vinod Koul
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dmaengine: xilinx_dma: Fix race condition in the driver for multiple descriptor scenario 



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: default avatarKedareswara rao Appana <appanad@xilinx.com>
Signed-off-by: default avatarVinod Koul <vinod.koul@intel.com>
parent fe0503e1

drivers/dma/xilinx/xilinx_dma.c

+84 −51
Original line number Diff line number Diff line
@@ -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);

}



/**
@@ -729,17 +752,27 @@ 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;

	}

}



/**

 * xilinx_dma_chan_handle_cyclic - Cyclic dma callback
@@ -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);
@@ -858,23 +912,21 @@ 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");