Re: [PATCH] Revert "net: qcom/emac: enforce DMA address restrictions"

[David Miller]

From: Timur Tabi 
Date: Thu, 12 Oct 2017 12:42:04 -0500

> This reverts commit df1ec1b9d0df57e96011f175418dc95b1af46821.
> 
> It turns out that memory allocated via dma_alloc_coherent is always
> aligned to the size of the buffer, so there's no way the RRD and RFD
> can ever be in separate 32-bit regions.
> 
> Signed-off-by: Timur Tabi 

Applied, thanks.

[PATCH] Revert "net: qcom/emac: enforce DMA address restrictions"

[Timur Tabi]

This reverts commit df1ec1b9d0df57e96011f175418dc95b1af46821.

It turns out that memory allocated via dma_alloc_coherent is always
aligned to the size of the buffer, so there's no way the RRD and RFD
can ever be in separate 32-bit regions.

Signed-off-by: Timur Tabi 
---
 drivers/net/ethernet/qualcomm/emac/emac-mac.c | 39 +++
 1 file changed, 15 insertions(+), 24 deletions(-)

diff --git a/drivers/net/ethernet/qualcomm/emac/emac-mac.c 
b/drivers/net/ethernet/qualcomm/emac/emac-mac.c
index 0f5ece5d9507..9cbb27263742 100644
--- a/drivers/net/ethernet/qualcomm/emac/emac-mac.c
+++ b/drivers/net/ethernet/qualcomm/emac/emac-mac.c
@@ -734,11 +734,6 @@ static int emac_rx_descs_alloc(struct emac_adapter *adpt)
rx_q->rrd.size = rx_q->rrd.count * (adpt->rrd_size * 4);
rx_q->rfd.size = rx_q->rfd.count * (adpt->rfd_size * 4);
 
-   /* Check if the RRD and RFD are aligned properly, and if not, adjust. */
-   if (upper_32_bits(ring_header->dma_addr) !=
-   upper_32_bits(ring_header->dma_addr + ALIGN(rx_q->rrd.size, 8)))
-   ring_header->used = ALIGN(rx_q->rrd.size, 8);
-
rx_q->rrd.dma_addr = ring_header->dma_addr + ring_header->used;
rx_q->rrd.v_addr   = ring_header->v_addr + ring_header->used;
ring_header->used += ALIGN(rx_q->rrd.size, 8);
@@ -772,18 +767,11 @@ int emac_mac_rx_tx_rings_alloc_all(struct emac_adapter 
*adpt)
 
/* Ring DMA buffer. Each ring may need up to 8 bytes for alignment,
 * hence the additional padding bytes are allocated.
-*
-* Also double the memory allocated for the RRD so that we can
-* re-align it if necessary.  The EMAC has a restriction that the
-* upper 32 bits of the base addresses for the RFD and RRD rings
-* must be the same.  It is extremely unlikely that this is not the
-* case, since the rings are only a few KB in size.  However, we
-* need to check for this anyway, and if the two rings are not
-* compliant, then we re-align.
 */
-   ring_header->size = ALIGN(num_tx_descs * (adpt->tpd_size * 4), 8) +
-   ALIGN(num_rx_descs * (adpt->rfd_size * 4), 8) +
-   ALIGN(num_rx_descs * (adpt->rrd_size * 4), 8) * 2;
+   ring_header->size = num_tx_descs * (adpt->tpd_size * 4) +
+   num_rx_descs * (adpt->rfd_size * 4) +
+   num_rx_descs * (adpt->rrd_size * 4) +
+   8 + 2 * 8; /* 8 byte per one Tx and two Rx rings */
 
ring_header->used = 0;
ring_header->v_addr = dma_zalloc_coherent(dev, ring_header->size,
@@ -792,23 +780,26 @@ int emac_mac_rx_tx_rings_alloc_all(struct emac_adapter 
*adpt)
if (!ring_header->v_addr)
return -ENOMEM;
 
-   ret = emac_rx_descs_alloc(adpt);
-   if (ret) {
-   netdev_err(adpt->netdev, "error: Rx Queue alloc failed\n");
-   goto err_alloc_rx;
-   }
+   ring_header->used = ALIGN(ring_header->dma_addr, 8) -
+   ring_header->dma_addr;
 
ret = emac_tx_q_desc_alloc(adpt, >tx_q);
if (ret) {
-   netdev_err(adpt->netdev, "transmit queue allocation failed\n");
+   netdev_err(adpt->netdev, "error: Tx Queue alloc failed\n");
goto err_alloc_tx;
}
 
+   ret = emac_rx_descs_alloc(adpt);
+   if (ret) {
+   netdev_err(adpt->netdev, "error: Rx Queue alloc failed\n");
+   goto err_alloc_rx;
+   }
+
return 0;
 
-err_alloc_tx:
-   emac_rx_q_bufs_free(adpt);
 err_alloc_rx:
+   emac_tx_q_bufs_free(adpt);
+err_alloc_tx:
dma_free_coherent(dev, ring_header->size,
  ring_header->v_addr, ring_header->dma_addr);
 
-- 
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Technologies, Inc.  Qualcomm Technologies, Inc. is a member of the
Code Aurora Forum, a Linux Foundation Collaborative Project.