ARM: OMAP2+: critical DRA7xx fix for v4.5-rc

Force the DRA7xx Ethernet internal clock source to stay enabled
per TI erratum i877:

Otherwise, if the Ethernet internal clock source is disabled, the
chip will age prematurely, and the RGMII I/O timing will soon
fail to meet the delay time and skew specifications for 1000Mbps

This fix should go in as soon as possible.

Basic build, boot, and PM test results are available here:
ARM: dts: dra7: do not gate cpsw clock due to errata i877

Errata id: i877

The RGMII 1000 Mbps Transmit timing is based on the output clock
(rgmiin_txc) being driven relative to the rising edge of an internal
clock and the output control/data (rgmiin_txctl/txd) being driven relative
to the falling edge of an internal clock source. If the internal clock
source is allowed to be static low (i.e., disabled) for an extended period
of time then when the clock is actually enabled the timing delta between
the rising edge and falling edge can change over the lifetime of the
device. This can result in the device switching characteristics degrading
over time, and eventually failing to meet the Data Manual Delay Time/Skew
To maintain RGMII 1000 Mbps IO Timings, SW should minimize the
duration that the Ethernet internal clock source is disabled. Note that
the device reset state for the Ethernet clock is "disabled".
Other RGMII modes (10 Mbps, 100Mbps) are not affected

If the SoC Ethernet interface(s) are used in RGMII mode at 1000 Mbps,
SW should minimize the time the Ethernet internal clock source is disabled
to a maximum of 200 hours in a device life cycle. This is done by enabling
the clock as early as possible in IPL (QNX) or SPL/u-boot (Linux/Android)
by setting the register CM_GMAC_CLKSTCTRL[1:0]CLKTRCTRL = 0x2:SW_WKUP.

So, do not allow to gate the cpsw clocks using ti,no-idle property in
cpsw node assuming 1000 Mbps is being used all the time. If someone does
not need 1000 Mbps and wants to gate clocks to cpsw, this property needs
to be deleted in their respective board files.

Signed-off-by: Mugunthan V N <>
Signed-off-by: Grygorii Strashko <>
Signed-off-by: Lokesh Vutla <>
Cc: <>
Signed-off-by: Paul Walmsley <>

1 file changed