From: Mugunthan V N <mugunthanvnm@xxxxxx> Errata id: i877 Description: ------------ 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 specs. 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 Workaround: ----------- 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 <mugunthanvnm@xxxxxx> Signed-off-by: Grygorii Strashko <grygorii.strashko@xxxxxx> Signed-off-by: Lokesh Vutla <lokeshvutla@xxxxxx> --- arch/arm/boot/dts/dra7.dtsi | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/arch/arm/boot/dts/dra7.dtsi b/arch/arm/boot/dts/dra7.dtsi index 6a4572a..340b657 100644 --- a/arch/arm/boot/dts/dra7.dtsi +++ b/arch/arm/boot/dts/dra7.dtsi @@ -1466,6 +1466,16 @@ 0x48485200 0x2E00>; #address-cells = <1>; #size-cells = <1>; + + /* + * Do not allow gating of cpsw clock as workaround + * for errata i877. Keeping internal clock disabled + * causes the device switching characteristics + * to degrade over time and eventually fail to meet + * the data manual delay time/skew specs. + */ + ti,no-idle; + /* * rx_thresh_pend * rx_pend -- 2.1.4 -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
