Patchwork [v4,1/1] net: ethernet: davinci_cpdma: Add boundary for rx and tx descriptors

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Submitter Mugunthan V N
Date Jan. 17, 2013, 12:10 a.m.
Message ID <1358381405-7247-1-git-send-email-mugunthanvnm@ti.com>
Download mbox | patch
Permalink /patch/213103/
State Changes Requested
Delegated to: David Miller
Headers show

Comments

Mugunthan V N - Jan. 17, 2013, 12:10 a.m.
When there is heavy transmission traffic in the CPDMA, then Rx descriptors
memory is also utilized as tx desc memory looses all rx descriptors and the
driver stops working then.

This patch adds boundary for tx and rx descriptors in bd ram dividing the
descriptor memory to ensure that during heavy transmission tx doesn't use
rx descriptors.

This patch is already applied to davinci_emac driver, since CPSW and
davici_dmac shares the same CPDMA, moving the boundry seperation from
Davinci EMAC driver to CPDMA driver which was done in the following
commit

commit 86d8c07ff2448eb4e860e50f34ef6ee78e45c40c
Author: Sascha Hauer <s.hauer@pengutronix.de>
Date:   Tue Jan 3 05:27:47 2012 +0000

    net/davinci: do not use all descriptors for tx packets

    The driver uses a shared pool for both rx and tx descriptors.
    During open it queues fixed number of 128 descriptors for receive
    packets. For each received packet it tries to queue another
    descriptor. If this fails the descriptor is lost for rx.
    The driver has no limitation on tx descriptors to use, so it
    can happen during a nmap / ping -f attack that the driver
    allocates all descriptors for tx and looses all rx descriptors.
    The driver stops working then.
    To fix this limit the number of tx descriptors used to half of
    the descriptors available, the rx path uses the other half.

    Tested on a custom board using nmap / ping -f to the board from
    two different hosts.

Signed-off-by: Mugunthan V N <mugunthanvnm@ti.com>
---
Changes from v3
* Changed multiline commenting as per networking style

 drivers/net/ethernet/ti/cpsw.c          |    9 ++++++
 drivers/net/ethernet/ti/davinci_cpdma.c |   51 ++++++++++++++++++++++++++-----
 drivers/net/ethernet/ti/davinci_cpdma.h |    1 +
 drivers/net/ethernet/ti/davinci_emac.c  |   13 ++++----
 4 files changed, 61 insertions(+), 13 deletions(-)
Christian Riesch - Jan. 17, 2013, 8:37 a.m.
Hi,

On 2013-01-17 01:10, Mugunthan V N wrote:
> When there is heavy transmission traffic in the CPDMA, then Rx descriptors
> memory is also utilized as tx desc memory looses all rx descriptors and the
> driver stops working then.
>
> This patch adds boundary for tx and rx descriptors in bd ram dividing the
> descriptor memory to ensure that during heavy transmission tx doesn't use
> rx descriptors.
>
> This patch is already applied to davinci_emac driver, since CPSW and
> davici_dmac shares the same CPDMA, moving the boundry seperation from
> Davinci EMAC driver to CPDMA driver which was done in the following
> commit
>
> commit 86d8c07ff2448eb4e860e50f34ef6ee78e45c40c
> Author: Sascha Hauer <s.hauer@pengutronix.de>
> Date:   Tue Jan 3 05:27:47 2012 +0000
>
>      net/davinci: do not use all descriptors for tx packets
>
>      The driver uses a shared pool for both rx and tx descriptors.
>      During open it queues fixed number of 128 descriptors for receive
>      packets. For each received packet it tries to queue another
>      descriptor. If this fails the descriptor is lost for rx.
>      The driver has no limitation on tx descriptors to use, so it
>      can happen during a nmap / ping -f attack that the driver
>      allocates all descriptors for tx and looses all rx descriptors.
>      The driver stops working then.
>      To fix this limit the number of tx descriptors used to half of
>      the descriptors available, the rx path uses the other half.
>
>      Tested on a custom board using nmap / ping -f to the board from
>      two different hosts.
>
> Signed-off-by: Mugunthan V N <mugunthanvnm@ti.com>
> ---
> Changes from v3
> * Changed multiline commenting as per networking style
>
>   drivers/net/ethernet/ti/cpsw.c          |    9 ++++++
>   drivers/net/ethernet/ti/davinci_cpdma.c |   51 ++++++++++++++++++++++++++-----
>   drivers/net/ethernet/ti/davinci_cpdma.h |    1 +
>   drivers/net/ethernet/ti/davinci_emac.c  |   13 ++++----
>   4 files changed, 61 insertions(+), 13 deletions(-)
>
> diff --git a/drivers/net/ethernet/ti/cpsw.c b/drivers/net/ethernet/ti/cpsw.c
> index 3772804..b35e6a7 100644
> --- a/drivers/net/ethernet/ti/cpsw.c
> +++ b/drivers/net/ethernet/ti/cpsw.c
> @@ -374,6 +374,9 @@ void cpsw_tx_handler(void *token, int len, int status)
>   	struct net_device	*ndev = skb->dev;
>   	struct cpsw_priv	*priv = netdev_priv(ndev);
>
> +	/* Check whether the queue is stopped due to stalled tx dma, if the
> +	 * queue is stopped then start the queue as we have free desc for tx
> +	 */
>   	if (unlikely(netif_queue_stopped(ndev)))
>   		netif_start_queue(ndev);
>   	cpts_tx_timestamp(&priv->cpts, skb);
> @@ -736,6 +739,12 @@ static netdev_tx_t cpsw_ndo_start_xmit(struct sk_buff *skb,
>   		goto fail;
>   	}
>
> +	/* If there is no more tx desc left free then we need to
> +	 * tell the kernel to stop sending us tx frames.
> +	 */
> +	if (unlikely(cpdma_check_free_tx_desc(priv->txch)))
> +		netif_stop_queue(ndev);
> +
>   	return NETDEV_TX_OK;
>   fail:
>   	priv->stats.tx_dropped++;
> diff --git a/drivers/net/ethernet/ti/davinci_cpdma.c b/drivers/net/ethernet/ti/davinci_cpdma.c
> index 4995673..4f6d82f 100644
> --- a/drivers/net/ethernet/ti/davinci_cpdma.c
> +++ b/drivers/net/ethernet/ti/davinci_cpdma.c
> @@ -105,13 +105,13 @@ struct cpdma_ctlr {
>   };
>
>   struct cpdma_chan {
> +	struct cpdma_desc __iomem	*head, *tail;
> +	void __iomem			*hdp, *cp, *rxfree;
>   	enum cpdma_state		state;
>   	struct cpdma_ctlr		*ctlr;
>   	int				chan_num;
>   	spinlock_t			lock;
> -	struct cpdma_desc __iomem	*head, *tail;
>   	int				count;
> -	void __iomem			*hdp, *cp, *rxfree;

I still do not see any benefit from this rearranging here.

>   	u32				mask;
>   	cpdma_handler_fn		handler;
>   	enum dma_data_direction		dir;
> @@ -217,17 +217,29 @@ desc_from_phys(struct cpdma_desc_pool *pool, dma_addr_t dma)
>   }
>
>   static struct cpdma_desc __iomem *
> -cpdma_desc_alloc(struct cpdma_desc_pool *pool, int num_desc)
> +cpdma_desc_alloc(struct cpdma_desc_pool *pool, int num_desc, bool is_rx)
>   {
>   	unsigned long flags;
>   	int index;
> +	int desc_start;
> +	int desc_end;
>   	struct cpdma_desc __iomem *desc = NULL;
>
>   	spin_lock_irqsave(&pool->lock, flags);
>
> -	index = bitmap_find_next_zero_area(pool->bitmap, pool->num_desc, 0,
> -					   num_desc, 0);
> -	if (index < pool->num_desc) {
> +	if (is_rx) {
> +		desc_start = 0;
> +		desc_end = pool->num_desc/2;
> +		index = bitmap_find_next_zero_area(pool->bitmap,
> +				pool->num_desc/2, 0, num_desc, 0);

Duplicate calls of bitmap_find_next_zero_area, see a few lines below.

> +	 } else {
> +		desc_start = pool->num_desc/2;
> +		desc_end = pool->num_desc;
> +	}
> +
> +	index = bitmap_find_next_zero_area(pool->bitmap,
> +				desc_end, desc_start, num_desc, 0);
> +	if (index < desc_end) {
>   		bitmap_set(pool->bitmap, index, num_desc);
>   		desc = pool->iomap + pool->desc_size * index;
>   		pool->used_desc++;
> @@ -660,6 +672,7 @@ int cpdma_chan_submit(struct cpdma_chan *chan, void *token, void *data,
>   	unsigned long			flags;
>   	u32				mode;
>   	int				ret = 0;
> +	bool                            is_rx;
>
>   	spin_lock_irqsave(&chan->lock, flags);
>
> @@ -668,7 +681,8 @@ int cpdma_chan_submit(struct cpdma_chan *chan, void *token, void *data,
>   		goto unlock_ret;
>   	}
>
> -	desc = cpdma_desc_alloc(ctlr->pool, 1);
> +	is_rx = (chan->rxfree != 0);

I guess you should use is_rx_chan() here.

> +	desc = cpdma_desc_alloc(ctlr->pool, 1, is_rx);
>   	if (!desc) {
>   		chan->stats.desc_alloc_fail++;
>   		ret = -ENOMEM;
> @@ -704,6 +718,29 @@ unlock_ret:
>   }
>   EXPORT_SYMBOL_GPL(cpdma_chan_submit);
>
> +bool cpdma_check_free_tx_desc(struct cpdma_chan *chan)
> +{
> +	unsigned long flags;
> +	int index;
> +	bool ret;
> +	struct cpdma_ctlr	*ctlr = chan->ctlr;
> +	struct cpdma_desc_pool	*pool = ctlr->pool;
> +
> +	spin_lock_irqsave(&pool->lock, flags);
> +
> +	index = bitmap_find_next_zero_area(pool->bitmap,
> +				pool->num_desc, pool->num_desc/2, 1, 0);

I still wonder if using two separate descriptor pools for rx and tx 
would be a nicer implementation. In this case you could just use 
bitmap_full here, right? And the two pools would have separate 
spinlocks, so rx could not lock tx and vice versa (but as I wrote in an 
earlier email, I am a newbie here, so I don't know if this would be 
beneficial).

Regards, Christian

> +
> +	if (index < pool->num_desc)
> +		ret = true;
> +	else
> +		ret = false;
> +
> +	spin_unlock_irqrestore(&pool->lock, flags);
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(cpdma_check_free_tx_desc);
> +
>   static void __cpdma_chan_free(struct cpdma_chan *chan,
>   			      struct cpdma_desc __iomem *desc,
>   			      int outlen, int status)
> diff --git a/drivers/net/ethernet/ti/davinci_cpdma.h b/drivers/net/ethernet/ti/davinci_cpdma.h
> index afa19a0..8d2aeb2 100644
> --- a/drivers/net/ethernet/ti/davinci_cpdma.h
> +++ b/drivers/net/ethernet/ti/davinci_cpdma.h
> @@ -88,6 +88,7 @@ int cpdma_chan_process(struct cpdma_chan *chan, int quota);
>   int cpdma_ctlr_int_ctrl(struct cpdma_ctlr *ctlr, bool enable);
>   void cpdma_ctlr_eoi(struct cpdma_ctlr *ctlr);
>   int cpdma_chan_int_ctrl(struct cpdma_chan *chan, bool enable);
> +bool cpdma_check_free_tx_desc(struct cpdma_chan *chan);
>
>   enum cpdma_control {
>   	CPDMA_CMD_IDLE,			/* write-only */
> diff --git a/drivers/net/ethernet/ti/davinci_emac.c b/drivers/net/ethernet/ti/davinci_emac.c
> index 8478d98..1c97c81 100644
> --- a/drivers/net/ethernet/ti/davinci_emac.c
> +++ b/drivers/net/ethernet/ti/davinci_emac.c
> @@ -120,7 +120,6 @@ static const char emac_version_string[] = "TI DaVinci EMAC Linux v6.1";
>   #define EMAC_DEF_TX_CH			(0) /* Default 0th channel */
>   #define EMAC_DEF_RX_CH			(0) /* Default 0th channel */
>   #define EMAC_DEF_RX_NUM_DESC		(128)
> -#define EMAC_DEF_TX_NUM_DESC		(128)
>   #define EMAC_DEF_MAX_TX_CH		(1) /* Max TX channels configured */
>   #define EMAC_DEF_MAX_RX_CH		(1) /* Max RX channels configured */
>   #define EMAC_POLL_WEIGHT		(64) /* Default NAPI poll weight */
> @@ -342,7 +341,6 @@ struct emac_priv {
>   	u32 mac_hash2;
>   	u32 multicast_hash_cnt[EMAC_NUM_MULTICAST_BITS];
>   	u32 rx_addr_type;
> -	atomic_t cur_tx;
>   	const char *phy_id;
>   #ifdef CONFIG_OF
>   	struct device_node *phy_node;
> @@ -1050,10 +1048,10 @@ static void emac_tx_handler(void *token, int len, int status)
>   {
>   	struct sk_buff		*skb = token;
>   	struct net_device	*ndev = skb->dev;
> -	struct emac_priv	*priv = netdev_priv(ndev);
> -
> -	atomic_dec(&priv->cur_tx);
>
> +	/* Check whether the queue is stopped due to stalled tx dma, if the
> +	 * queue is stopped then start the queue as we have free desc for tx
> +	 */
>   	if (unlikely(netif_queue_stopped(ndev)))
>   		netif_start_queue(ndev);
>   	ndev->stats.tx_packets++;
> @@ -1101,7 +1099,10 @@ static int emac_dev_xmit(struct sk_buff *skb, struct net_device *ndev)
>   		goto fail_tx;
>   	}
>
> -	if (atomic_inc_return(&priv->cur_tx) >= EMAC_DEF_TX_NUM_DESC)
> +	/* If there is no more tx desc left free then we need to
> +	 * tell the kernel to stop sending us tx frames.
> +	 */
> +	if (unlikely(cpdma_check_free_tx_desc(priv->txch)))
>   		netif_stop_queue(ndev);
>
>   	return NETDEV_TX_OK;
>

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Mugunthan V N - Jan. 17, 2013, 9:30 a.m.
Christian

On 1/17/2013 2:07 PM, Christian Riesch wrote:
> Hi,
>
> On 2013-01-17 01:10, Mugunthan V N wrote:
>> When there is heavy transmission traffic in the CPDMA, then Rx 
>> descriptors
>> memory is also utilized as tx desc memory looses all rx descriptors 
>> and the
>> driver stops working then.
>>
>> This patch adds boundary for tx and rx descriptors in bd ram dividing 
>> the
>> descriptor memory to ensure that during heavy transmission tx doesn't 
>> use
>> rx descriptors.
>>
>> This patch is already applied to davinci_emac driver, since CPSW and
>> davici_dmac shares the same CPDMA, moving the boundry seperation from
>> Davinci EMAC driver to CPDMA driver which was done in the following
>> commit
>>
>> commit 86d8c07ff2448eb4e860e50f34ef6ee78e45c40c
>> Author: Sascha Hauer <s.hauer@pengutronix.de>
>> Date:   Tue Jan 3 05:27:47 2012 +0000
>>
>>      net/davinci: do not use all descriptors for tx packets
>>
>>      The driver uses a shared pool for both rx and tx descriptors.
>>      During open it queues fixed number of 128 descriptors for receive
>>      packets. For each received packet it tries to queue another
>>      descriptor. If this fails the descriptor is lost for rx.
>>      The driver has no limitation on tx descriptors to use, so it
>>      can happen during a nmap / ping -f attack that the driver
>>      allocates all descriptors for tx and looses all rx descriptors.
>>      The driver stops working then.
>>      To fix this limit the number of tx descriptors used to half of
>>      the descriptors available, the rx path uses the other half.
>>
>>      Tested on a custom board using nmap / ping -f to the board from
>>      two different hosts.
>>
>> Signed-off-by: Mugunthan V N <mugunthanvnm@ti.com>
>> ---
>> Changes from v3
>> * Changed multiline commenting as per networking style
>>
>>   drivers/net/ethernet/ti/cpsw.c          |    9 ++++++
>>   drivers/net/ethernet/ti/davinci_cpdma.c |   51 
>> ++++++++++++++++++++++++++-----
>>   drivers/net/ethernet/ti/davinci_cpdma.h |    1 +
>>   drivers/net/ethernet/ti/davinci_emac.c  |   13 ++++----
>>   4 files changed, 61 insertions(+), 13 deletions(-)
>>
>> diff --git a/drivers/net/ethernet/ti/cpsw.c 
>> b/drivers/net/ethernet/ti/cpsw.c
>> index 3772804..b35e6a7 100644
>> --- a/drivers/net/ethernet/ti/cpsw.c
>> +++ b/drivers/net/ethernet/ti/cpsw.c
>> @@ -374,6 +374,9 @@ void cpsw_tx_handler(void *token, int len, int 
>> status)
>>       struct net_device    *ndev = skb->dev;
>>       struct cpsw_priv    *priv = netdev_priv(ndev);
>>
>> +    /* Check whether the queue is stopped due to stalled tx dma, if the
>> +     * queue is stopped then start the queue as we have free desc 
>> for tx
>> +     */
>>       if (unlikely(netif_queue_stopped(ndev)))
>>           netif_start_queue(ndev);
>>       cpts_tx_timestamp(&priv->cpts, skb);
>> @@ -736,6 +739,12 @@ static netdev_tx_t cpsw_ndo_start_xmit(struct 
>> sk_buff *skb,
>>           goto fail;
>>       }
>>
>> +    /* If there is no more tx desc left free then we need to
>> +     * tell the kernel to stop sending us tx frames.
>> +     */
>> +    if (unlikely(cpdma_check_free_tx_desc(priv->txch)))
>> +        netif_stop_queue(ndev);
>> +
>>       return NETDEV_TX_OK;
>>   fail:
>>       priv->stats.tx_dropped++;
>> diff --git a/drivers/net/ethernet/ti/davinci_cpdma.c 
>> b/drivers/net/ethernet/ti/davinci_cpdma.c
>> index 4995673..4f6d82f 100644
>> --- a/drivers/net/ethernet/ti/davinci_cpdma.c
>> +++ b/drivers/net/ethernet/ti/davinci_cpdma.c
>> @@ -105,13 +105,13 @@ struct cpdma_ctlr {
>>   };
>>
>>   struct cpdma_chan {
>> +    struct cpdma_desc __iomem    *head, *tail;
>> +    void __iomem            *hdp, *cp, *rxfree;
>>       enum cpdma_state        state;
>>       struct cpdma_ctlr        *ctlr;
>>       int                chan_num;
>>       spinlock_t            lock;
>> -    struct cpdma_desc __iomem    *head, *tail;
>>       int                count;
>> -    void __iomem            *hdp, *cp, *rxfree;
>
> I still do not see any benefit from this rearranging here.
This is just code cleanup and doesn't provide any benefit.
>
>>       u32                mask;
>>       cpdma_handler_fn        handler;
>>       enum dma_data_direction        dir;
>> @@ -217,17 +217,29 @@ desc_from_phys(struct cpdma_desc_pool *pool, 
>> dma_addr_t dma)
>>   }
>>
>>   static struct cpdma_desc __iomem *
>> -cpdma_desc_alloc(struct cpdma_desc_pool *pool, int num_desc)
>> +cpdma_desc_alloc(struct cpdma_desc_pool *pool, int num_desc, bool 
>> is_rx)
>>   {
>>       unsigned long flags;
>>       int index;
>> +    int desc_start;
>> +    int desc_end;
>>       struct cpdma_desc __iomem *desc = NULL;
>>
>>       spin_lock_irqsave(&pool->lock, flags);
>>
>> -    index = bitmap_find_next_zero_area(pool->bitmap, pool->num_desc, 0,
>> -                       num_desc, 0);
>> -    if (index < pool->num_desc) {
>> +    if (is_rx) {
>> +        desc_start = 0;
>> +        desc_end = pool->num_desc/2;
>> +        index = bitmap_find_next_zero_area(pool->bitmap,
>> +                pool->num_desc/2, 0, num_desc, 0);
>
> Duplicate calls of bitmap_find_next_zero_area, see a few lines below.
Will fix this in next patch version
>
>> +     } else {
>> +        desc_start = pool->num_desc/2;
>> +        desc_end = pool->num_desc;
>> +    }
>> +
>> +    index = bitmap_find_next_zero_area(pool->bitmap,
>> +                desc_end, desc_start, num_desc, 0);
>> +    if (index < desc_end) {
>>           bitmap_set(pool->bitmap, index, num_desc);
>>           desc = pool->iomap + pool->desc_size * index;
>>           pool->used_desc++;
>> @@ -660,6 +672,7 @@ int cpdma_chan_submit(struct cpdma_chan *chan, 
>> void *token, void *data,
>>       unsigned long            flags;
>>       u32                mode;
>>       int                ret = 0;
>> +    bool                            is_rx;
>>
>>       spin_lock_irqsave(&chan->lock, flags);
>>
>> @@ -668,7 +681,8 @@ int cpdma_chan_submit(struct cpdma_chan *chan, 
>> void *token, void *data,
>>           goto unlock_ret;
>>       }
>>
>> -    desc = cpdma_desc_alloc(ctlr->pool, 1);
>> +    is_rx = (chan->rxfree != 0);
>
> I guess you should use is_rx_chan() here.
Will change this to MACRO.
>
>> +    desc = cpdma_desc_alloc(ctlr->pool, 1, is_rx);
>>       if (!desc) {
>>           chan->stats.desc_alloc_fail++;
>>           ret = -ENOMEM;
>> @@ -704,6 +718,29 @@ unlock_ret:
>>   }
>>   EXPORT_SYMBOL_GPL(cpdma_chan_submit);
>>
>> +bool cpdma_check_free_tx_desc(struct cpdma_chan *chan)
>> +{
>> +    unsigned long flags;
>> +    int index;
>> +    bool ret;
>> +    struct cpdma_ctlr    *ctlr = chan->ctlr;
>> +    struct cpdma_desc_pool    *pool = ctlr->pool;
>> +
>> +    spin_lock_irqsave(&pool->lock, flags);
>> +
>> +    index = bitmap_find_next_zero_area(pool->bitmap,
>> +                pool->num_desc, pool->num_desc/2, 1, 0);
>
> I still wonder if using two separate descriptor pools for rx and tx 
> would be a nicer implementation. In this case you could just use 
> bitmap_full here, right? And the two pools would have separate 
> spinlocks, so rx could not lock tx and vice versa (but as I wrote in 
> an earlier email, I am a newbie here, so I don't know if this would be 
> beneficial).
>
I don't think having two separate pool with separate lock will improve 
performance, i have not seen any issues using one pool with one lock.

Regards
Mugunthan V N
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Patch

diff --git a/drivers/net/ethernet/ti/cpsw.c b/drivers/net/ethernet/ti/cpsw.c
index 3772804..b35e6a7 100644
--- a/drivers/net/ethernet/ti/cpsw.c
+++ b/drivers/net/ethernet/ti/cpsw.c
@@ -374,6 +374,9 @@  void cpsw_tx_handler(void *token, int len, int status)
 	struct net_device	*ndev = skb->dev;
 	struct cpsw_priv	*priv = netdev_priv(ndev);
 
+	/* Check whether the queue is stopped due to stalled tx dma, if the
+	 * queue is stopped then start the queue as we have free desc for tx
+	 */
 	if (unlikely(netif_queue_stopped(ndev)))
 		netif_start_queue(ndev);
 	cpts_tx_timestamp(&priv->cpts, skb);
@@ -736,6 +739,12 @@  static netdev_tx_t cpsw_ndo_start_xmit(struct sk_buff *skb,
 		goto fail;
 	}
 
+	/* If there is no more tx desc left free then we need to
+	 * tell the kernel to stop sending us tx frames.
+	 */
+	if (unlikely(cpdma_check_free_tx_desc(priv->txch)))
+		netif_stop_queue(ndev);
+
 	return NETDEV_TX_OK;
 fail:
 	priv->stats.tx_dropped++;
diff --git a/drivers/net/ethernet/ti/davinci_cpdma.c b/drivers/net/ethernet/ti/davinci_cpdma.c
index 4995673..4f6d82f 100644
--- a/drivers/net/ethernet/ti/davinci_cpdma.c
+++ b/drivers/net/ethernet/ti/davinci_cpdma.c
@@ -105,13 +105,13 @@  struct cpdma_ctlr {
 };
 
 struct cpdma_chan {
+	struct cpdma_desc __iomem	*head, *tail;
+	void __iomem			*hdp, *cp, *rxfree;
 	enum cpdma_state		state;
 	struct cpdma_ctlr		*ctlr;
 	int				chan_num;
 	spinlock_t			lock;
-	struct cpdma_desc __iomem	*head, *tail;
 	int				count;
-	void __iomem			*hdp, *cp, *rxfree;
 	u32				mask;
 	cpdma_handler_fn		handler;
 	enum dma_data_direction		dir;
@@ -217,17 +217,29 @@  desc_from_phys(struct cpdma_desc_pool *pool, dma_addr_t dma)
 }
 
 static struct cpdma_desc __iomem *
-cpdma_desc_alloc(struct cpdma_desc_pool *pool, int num_desc)
+cpdma_desc_alloc(struct cpdma_desc_pool *pool, int num_desc, bool is_rx)
 {
 	unsigned long flags;
 	int index;
+	int desc_start;
+	int desc_end;
 	struct cpdma_desc __iomem *desc = NULL;
 
 	spin_lock_irqsave(&pool->lock, flags);
 
-	index = bitmap_find_next_zero_area(pool->bitmap, pool->num_desc, 0,
-					   num_desc, 0);
-	if (index < pool->num_desc) {
+	if (is_rx) {
+		desc_start = 0;
+		desc_end = pool->num_desc/2;
+		index = bitmap_find_next_zero_area(pool->bitmap,
+				pool->num_desc/2, 0, num_desc, 0);
+	 } else {
+		desc_start = pool->num_desc/2;
+		desc_end = pool->num_desc;
+	}
+
+	index = bitmap_find_next_zero_area(pool->bitmap,
+				desc_end, desc_start, num_desc, 0);
+	if (index < desc_end) {
 		bitmap_set(pool->bitmap, index, num_desc);
 		desc = pool->iomap + pool->desc_size * index;
 		pool->used_desc++;
@@ -660,6 +672,7 @@  int cpdma_chan_submit(struct cpdma_chan *chan, void *token, void *data,
 	unsigned long			flags;
 	u32				mode;
 	int				ret = 0;
+	bool                            is_rx;
 
 	spin_lock_irqsave(&chan->lock, flags);
 
@@ -668,7 +681,8 @@  int cpdma_chan_submit(struct cpdma_chan *chan, void *token, void *data,
 		goto unlock_ret;
 	}
 
-	desc = cpdma_desc_alloc(ctlr->pool, 1);
+	is_rx = (chan->rxfree != 0);
+	desc = cpdma_desc_alloc(ctlr->pool, 1, is_rx);
 	if (!desc) {
 		chan->stats.desc_alloc_fail++;
 		ret = -ENOMEM;
@@ -704,6 +718,29 @@  unlock_ret:
 }
 EXPORT_SYMBOL_GPL(cpdma_chan_submit);
 
+bool cpdma_check_free_tx_desc(struct cpdma_chan *chan)
+{
+	unsigned long flags;
+	int index;
+	bool ret;
+	struct cpdma_ctlr	*ctlr = chan->ctlr;
+	struct cpdma_desc_pool	*pool = ctlr->pool;
+
+	spin_lock_irqsave(&pool->lock, flags);
+
+	index = bitmap_find_next_zero_area(pool->bitmap,
+				pool->num_desc, pool->num_desc/2, 1, 0);
+
+	if (index < pool->num_desc)
+		ret = true;
+	else
+		ret = false;
+
+	spin_unlock_irqrestore(&pool->lock, flags);
+	return ret;
+}
+EXPORT_SYMBOL_GPL(cpdma_check_free_tx_desc);
+
 static void __cpdma_chan_free(struct cpdma_chan *chan,
 			      struct cpdma_desc __iomem *desc,
 			      int outlen, int status)
diff --git a/drivers/net/ethernet/ti/davinci_cpdma.h b/drivers/net/ethernet/ti/davinci_cpdma.h
index afa19a0..8d2aeb2 100644
--- a/drivers/net/ethernet/ti/davinci_cpdma.h
+++ b/drivers/net/ethernet/ti/davinci_cpdma.h
@@ -88,6 +88,7 @@  int cpdma_chan_process(struct cpdma_chan *chan, int quota);
 int cpdma_ctlr_int_ctrl(struct cpdma_ctlr *ctlr, bool enable);
 void cpdma_ctlr_eoi(struct cpdma_ctlr *ctlr);
 int cpdma_chan_int_ctrl(struct cpdma_chan *chan, bool enable);
+bool cpdma_check_free_tx_desc(struct cpdma_chan *chan);
 
 enum cpdma_control {
 	CPDMA_CMD_IDLE,			/* write-only */
diff --git a/drivers/net/ethernet/ti/davinci_emac.c b/drivers/net/ethernet/ti/davinci_emac.c
index 8478d98..1c97c81 100644
--- a/drivers/net/ethernet/ti/davinci_emac.c
+++ b/drivers/net/ethernet/ti/davinci_emac.c
@@ -120,7 +120,6 @@  static const char emac_version_string[] = "TI DaVinci EMAC Linux v6.1";
 #define EMAC_DEF_TX_CH			(0) /* Default 0th channel */
 #define EMAC_DEF_RX_CH			(0) /* Default 0th channel */
 #define EMAC_DEF_RX_NUM_DESC		(128)
-#define EMAC_DEF_TX_NUM_DESC		(128)
 #define EMAC_DEF_MAX_TX_CH		(1) /* Max TX channels configured */
 #define EMAC_DEF_MAX_RX_CH		(1) /* Max RX channels configured */
 #define EMAC_POLL_WEIGHT		(64) /* Default NAPI poll weight */
@@ -342,7 +341,6 @@  struct emac_priv {
 	u32 mac_hash2;
 	u32 multicast_hash_cnt[EMAC_NUM_MULTICAST_BITS];
 	u32 rx_addr_type;
-	atomic_t cur_tx;
 	const char *phy_id;
 #ifdef CONFIG_OF
 	struct device_node *phy_node;
@@ -1050,10 +1048,10 @@  static void emac_tx_handler(void *token, int len, int status)
 {
 	struct sk_buff		*skb = token;
 	struct net_device	*ndev = skb->dev;
-	struct emac_priv	*priv = netdev_priv(ndev);
-
-	atomic_dec(&priv->cur_tx);
 
+	/* Check whether the queue is stopped due to stalled tx dma, if the
+	 * queue is stopped then start the queue as we have free desc for tx
+	 */
 	if (unlikely(netif_queue_stopped(ndev)))
 		netif_start_queue(ndev);
 	ndev->stats.tx_packets++;
@@ -1101,7 +1099,10 @@  static int emac_dev_xmit(struct sk_buff *skb, struct net_device *ndev)
 		goto fail_tx;
 	}
 
-	if (atomic_inc_return(&priv->cur_tx) >= EMAC_DEF_TX_NUM_DESC)
+	/* If there is no more tx desc left free then we need to
+	 * tell the kernel to stop sending us tx frames.
+	 */
+	if (unlikely(cpdma_check_free_tx_desc(priv->txch)))
 		netif_stop_queue(ndev);
 
 	return NETDEV_TX_OK;