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-rw-r--r--drivers/net/fec_mxc.c23
1 files changed, 22 insertions, 1 deletions
diff --git a/drivers/net/fec_mxc.c b/drivers/net/fec_mxc.c
index da95e285b7..ec5b9db660 100644
--- a/drivers/net/fec_mxc.c
+++ b/drivers/net/fec_mxc.c
@@ -560,7 +560,6 @@ static int fec_init(struct eth_device *dev, bd_t* bd)
}
memset(fec->tbd_base, 0, size);
fec_tbd_init(fec);
- flush_dcache_range((unsigned)fec->tbd_base, size);
}
/*
@@ -738,6 +737,28 @@ static int fec_send(struct eth_device *dev, void *packet, int length)
flush_dcache_range(addr, addr + size);
/*
+ * Below we read the DMA descriptor's last four bytes back from the
+ * DRAM. This is important in order to make sure that all WRITE
+ * operations on the bus that were triggered by previous cache FLUSH
+ * have completed.
+ *
+ * Otherwise, on MX28, it is possible to observe a corruption of the
+ * DMA descriptors. Please refer to schematic "Figure 1-2" in MX28RM
+ * for the bus structure of MX28. The scenario is as follows:
+ *
+ * 1) ARM core triggers a series of WRITEs on the AHB_ARB2 bus going
+ * to DRAM due to flush_dcache_range()
+ * 2) ARM core writes the FEC registers via AHB_ARB2
+ * 3) FEC DMA starts reading/writing from/to DRAM via AHB_ARB3
+ *
+ * Note that 2) does sometimes finish before 1) due to reordering of
+ * WRITE accesses on the AHB bus, therefore triggering 3) before the
+ * DMA descriptor is fully written into DRAM. This results in occasional
+ * corruption of the DMA descriptor.
+ */
+ readl(addr + size - 4);
+
+ /*
* Enable SmartDMA transmit task
*/
fec_tx_task_enable(fec);