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Commit 002f4557 authored by Florian Fainelli's avatar Florian Fainelli Committed by Greg Kroah-Hartman
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net: systemport: Rewrite __bcm_sysport_tx_reclaim() 




[ Upstream commit 484d802d0f2f29c335563fcac2a8facf174a1bbc ]

There is no need for complex checking between the last consumed index
and current consumed index, a simple subtraction will do.

This also eliminates the possibility of a permanent transmit queue stall
under the following conditions:

- one CPU bursts ring->size worth of traffic (up to 256 buffers), to the
  point where we run out of free descriptors, so we stop the transmit
  queue at the end of bcm_sysport_xmit()

- because of our locking, we have the transmit process disable
  interrupts which means we can be blocking the TX reclamation process

- when TX reclamation finally runs, we will be computing the difference
  between ring->c_index (last consumed index by SW) and what the HW
  reports through its register

- this register is masked with (ring->size - 1) = 0xff, which will lead
  to stripping the upper bits of the index (register is 16-bits wide)

- we will be computing last_tx_cn as 0, which means there is no work to
  be done, and we never wake-up the transmit queue, leaving it
  permanently disabled

A practical example is e.g: ring->c_index aka last_c_index = 12, we
pushed 256 entries, HW consumer index = 268, we mask it with 0xff = 12,
so last_tx_cn == 0, nothing happens.

Fixes: 80105bef ("net: systemport: add Broadcom SYSTEMPORT Ethernet MAC driver")
Signed-off-by: default avatarFlorian Fainelli <f.fainelli@gmail.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 4751804d

drivers/net/ethernet/broadcom/bcmsysport.c

+15 −18
Original line number Diff line number Diff line
@@ -707,37 +707,33 @@ static unsigned int __bcm_sysport_tx_reclaim(struct bcm_sysport_priv *priv, 
					     struct bcm_sysport_tx_ring *ring)

{

	struct net_device *ndev = priv->netdev;

	unsigned int c_index, last_c_index, last_tx_cn, num_tx_cbs;

	unsigned int pkts_compl = 0, bytes_compl = 0;

	unsigned int txbds_processed = 0;

	struct bcm_sysport_cb *cb;

	unsigned int txbds_ready;

	unsigned int c_index;

	u32 hw_ind;



	/* Compute how many descriptors have been processed since last call */

	hw_ind = tdma_readl(priv, TDMA_DESC_RING_PROD_CONS_INDEX(ring->index));

	c_index = (hw_ind >> RING_CONS_INDEX_SHIFT) & RING_CONS_INDEX_MASK;

	ring->p_index = (hw_ind & RING_PROD_INDEX_MASK);



	last_c_index = ring->c_index;

	num_tx_cbs = ring->size;



	c_index &= (num_tx_cbs - 1);



	if (c_index >= last_c_index)

		last_tx_cn = c_index - last_c_index;

	else

		last_tx_cn = num_tx_cbs - last_c_index + c_index;

	txbds_ready = (c_index - ring->c_index) & RING_CONS_INDEX_MASK;



	netif_dbg(priv, tx_done, ndev,

		  "ring=%d c_index=%d last_tx_cn=%d last_c_index=%d\n",

		  ring->index, c_index, last_tx_cn, last_c_index);

		  "ring=%d old_c_index=%u c_index=%u txbds_ready=%u\n",

		  ring->index, ring->c_index, c_index, txbds_ready);



	while (last_tx_cn-- > 0) {

		cb = ring->cbs + last_c_index;

	while (txbds_processed < txbds_ready) {

		cb = &ring->cbs[ring->clean_index];

		bcm_sysport_tx_reclaim_one(priv, cb, &bytes_compl, &pkts_compl);



		ring->desc_count++;

		last_c_index++;

		last_c_index &= (num_tx_cbs - 1);

		txbds_processed++;



		if (likely(ring->clean_index < ring->size - 1))

			ring->clean_index++;

		else

			ring->clean_index = 0;

	}



	ring->c_index = c_index;
@@ -1207,6 +1203,7 @@ static int bcm_sysport_init_tx_ring(struct bcm_sysport_priv *priv, 
	netif_tx_napi_add(priv->netdev, &ring->napi, bcm_sysport_tx_poll, 64);

	ring->index = index;

	ring->size = size;

	ring->clean_index = 0;

	ring->alloc_size = ring->size;

	ring->desc_cpu = p;

	ring->desc_count = ring->size;

drivers/net/ethernet/broadcom/bcmsysport.h

+1 −1
Original line number Diff line number Diff line
@@ -638,7 +638,7 @@ struct bcm_sysport_tx_ring { 
	unsigned int	desc_count;	/* Number of descriptors */

	unsigned int	curr_desc;	/* Current descriptor */

	unsigned int	c_index;	/* Last consumer index */

	unsigned int	p_index;	/* Current producer index */

	unsigned int	clean_index;	/* Current clean index */

	struct bcm_sysport_cb *cbs;	/* Transmit control blocks */

	struct dma_desc	*desc_cpu;	/* CPU view of the descriptor */

	struct bcm_sysport_priv *priv;	/* private context backpointer */