bgmac: backport small DMA fix

It's supposed to significantly improve performance but doesn't seem to
affect Northstar unfortunately. It seems only some other platforms were
limited because of this DMA setup mistake.

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>

1 files changed, 59 insertions, 0 deletions

diff --git a/target/linux/generic/patches-4.4/077-0005-bgmac-stop-clearing-DMA-receive-control-register-rig.patch b/target/linux/generic/patches-4.4/077-0005-bgmac-stop-clearing-DMA-receive-control-register-rig.patch
new file mode 100644
index 0000000000..0c4767895b
--- /dev/null
+++ b/target/linux/generic/patches-4.4/077-0005-bgmac-stop-clearing-DMA-receive-control-register-rig.patch
@@ -0,0 +1,59 @@
+From fcdefccac976ee51dd6071832b842d8fb41c479c Mon Sep 17 00:00:00 2001
+From: Andy Gospodarek <gospo@broadcom.com>
+Date: Mon, 31 Oct 2016 13:32:03 -0400
+Subject: [PATCH] bgmac: stop clearing DMA receive control register right after
+ it is set
+
+Current bgmac code initializes some DMA settings in the receive control
+register for some hardware and then immediately clears those settings.
+Not clearing those settings results in ~420Mbps *improvement* in
+throughput; this system can now receive frames at line-rate on Broadcom
+5871x hardware compared to ~520Mbps today.  I also tested a few other
+values but found there to be no discernible difference in CPU
+utilization even if burst size and prefetching values are different.
+
+On the hardware tested there was no need to keep the code that cleared
+all but bits 16-17, but since there is a wide variety of hardware that
+used this driver (I did not look at all hardware docs for hardware using
+this IP block), I find it wise to move this call up and clear bits just
+after reading the default value from the hardware rather than completely
+removing it.
+
+This is a good candidate for -stable >=3.14 since that is when the code
+that was supposed to improve performance (but did not) was introduced.
+
+Signed-off-by: Andy Gospodarek <gospo@broadcom.com>
+Fixes: 56ceecde1f29 ("bgmac: initialize the DMA controller of core...")
+Cc: Hauke Mehrtens <hauke@hauke-m.de>
+Acked-by: Hauke Mehrtens <hauke@hauke-m.de>
+Signed-off-by: David S. Miller <davem@davemloft.net>
+---
+ drivers/net/ethernet/broadcom/bgmac.c | 5 ++++-
+ 1 file changed, 4 insertions(+), 1 deletion(-)
+
+diff --git a/drivers/net/ethernet/broadcom/bgmac.c b/drivers/net/ethernet/broadcom/bgmac.c
+index 31ca204..91cbf92 100644
+--- a/drivers/net/ethernet/broadcom/bgmac.c
++++ b/drivers/net/ethernet/broadcom/bgmac.c
+@@ -307,6 +307,10 @@ static void bgmac_dma_rx_enable(struct bgmac *bgmac,
+ 	u32 ctl;
+ 
+ 	ctl = bgmac_read(bgmac, ring->mmio_base + BGMAC_DMA_RX_CTL);
++
++	/* preserve ONLY bits 16-17 from current hardware value */
++	ctl &= BGMAC_DMA_RX_ADDREXT_MASK;
++
+ 	if (bgmac->feature_flags & BGMAC_FEAT_RX_MASK_SETUP) {
+ 		ctl &= ~BGMAC_DMA_RX_BL_MASK;
+ 		ctl |= BGMAC_DMA_RX_BL_128 << BGMAC_DMA_RX_BL_SHIFT;
+@@ -317,7 +321,6 @@ static void bgmac_dma_rx_enable(struct bgmac *bgmac,
+ 		ctl &= ~BGMAC_DMA_RX_PT_MASK;
+ 		ctl |= BGMAC_DMA_RX_PT_1 << BGMAC_DMA_RX_PT_SHIFT;
+ 	}
+-	ctl &= BGMAC_DMA_RX_ADDREXT_MASK;
+ 	ctl |= BGMAC_DMA_RX_ENABLE;
+ 	ctl |= BGMAC_DMA_RX_PARITY_DISABLE;
+ 	ctl |= BGMAC_DMA_RX_OVERFLOW_CONT;
+-- 
+2.10.1
+