[PATCH v2] sh_eth: use RNC mode for R8A7790/R87791

[Ben Dooks <ben.dooks@codethink.co.uk>]

The current behaviour of the sh_eth driver is not to use the RNC bit
for the receive ring. This means that every packet recieved is not only
generating an IRQ but it also stops the receive ring DMA as well until
the driver re-enables it after unloading the packet.

This means that a number of the following errors are generated due to
the receive packet FIFO overflowing due to nowhere to put packets:

	net eth0: Receive FIFO Overflow

I have tested the RMCR_RNC configuration with NFS root filesystem and
the driver has not failed yet.  There are further test reports from
Sergei Shtylov and others for both the R8A7790 and R8A7791.

There is also feedback fron Cao Minh Hiep[1] which reports the
same issue in (http://comments.gmane.org/gmane.linux.network/316285)
showing this fixes issues with losing UDP datagrams under iperf.

Tested-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Signed-off-by: Ben Dooks <ben.dooks@codethink.co.uk>

---
Cc: nobuhiro.iwamatsu.yj@renesas.com
Cc: magnus.damn@opensource.se
Cc: horms@verge.net.au
Cc: yoshihiro.shimoda.uh@renesas.com
Cc: cm-hiep@jinso.co.jp

Changes since v1:
	- Fixed title and body to contain R8A7791
	- Updated list of CC:
---
 drivers/net/ethernet/renesas/sh_eth.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/net/ethernet/renesas/sh_eth.c b/drivers/net/ethernet/renesas/sh_eth.c
index 6a9509c..1e3e5d2 100644
--- a/drivers/net/ethernet/renesas/sh_eth.c
+++ b/drivers/net/ethernet/renesas/sh_eth.c
@@ -468,6 +468,7 @@ static struct sh_eth_cpu_data r8a779x_data = {
 	.ecsr_value	= ECSR_PSRTO | ECSR_LCHNG | ECSR_ICD,
 	.ecsipr_value	= ECSIPR_PSRTOIP | ECSIPR_LCHNGIP | ECSIPR_ICDIP,
 	.eesipr_value	= 0x01ff009f,
+	.rmcr_value	= RMCR_RNC,
 
 	.tx_check	= EESR_FTC | EESR_CND | EESR_DLC | EESR_CD | EESR_RTO,
 	.eesr_err_check	= EESR_TWB | EESR_TABT | EESR_RABT | EESR_RFE |
-- 
2.0.0.rc2