On 26/08/14 11:15, Shawn Guo wrote: > On Sun, Aug 24, 2014 at 10:44:54AM +0100, Iain Paton wrote: >> On 23/08/14 10:11, Russell King wrote: >>> From: Rabeeh Khoury <[email protected]> >>> To: Shawn Guo <[email protected]> >>> >>> MDIO pad must be set open drain. >>> >>> Signed-off-by: Rabeeh Khoury <[email protected]> >>> Signed-off-by: Russell King <[email protected]> >>> --- >>> arch/arm/boot/dts/imx6qdl-microsom-ar8035.dtsi | 2 +- >>> 1 file changed, 1 insertion(+), 1 deletion(-) >>> >>> diff --git a/arch/arm/boot/dts/imx6qdl-microsom-ar8035.dtsi >>> b/arch/arm/boot/dts/imx6qdl-microsom-ar8035.dtsi >>> index d16066608e21..db9f45b2c573 100644 >>> --- a/arch/arm/boot/dts/imx6qdl-microsom-ar8035.dtsi >>> +++ b/arch/arm/boot/dts/imx6qdl-microsom-ar8035.dtsi >>> @@ -17,7 +17,7 @@ >>> enet { >>> pinctrl_microsom_enet_ar8035: microsom-enet-ar8035 { >>> fsl,pins = < >>> - MX6QDL_PAD_ENET_MDIO__ENET_MDIO 0x1b0b0 >>> + MX6QDL_PAD_ENET_MDIO__ENET_MDIO 0x1b8b0 >>> MX6QDL_PAD_ENET_MDC__ENET_MDC 0x1b0b0 >>> /* AR8035 reset */ >>> MX6QDL_PAD_KEY_ROW4__GPIO4_IO15 0x130b0 >>> >> >> Can you elaborate some more on the reasons for this? > > I just got the following text from Rabeeh explaining the change. > > "This patch is important for the MicroSOM implementation due to the > following details - > > 1. VIH of the Atheros phy is 1.7V. > 2. NVCC_ENET which is the power domain of the MDIO pad is driven by the > PHY's LDO (i.e. either 1.8v or 2.5v). > 3. The MicroSOM implements an onbouard 1.6kohm pull up to 3.3v (R3000). > > In the case the PHY's LDO was 1.8v then there would be only a 100mV > margin for the signal to be acknowledged as high (1.8v-1.7v). > Due to that setting the pad as an open drain will let the 1.6kohm pull > that signal high to 3.3 that assures enough margins to the PHY to be > acked as '1' logic. > > Notice that this change is not required to the SabreSD boards since that > hardware drives the NVCC_EIM power island from a 3.3v power rail." > >> >> I'd like to understand if it's something specific to the hardware on that >> board, or if other i.MX6 boards using the ar8035 are doing it wrong as well. > > So from text above, it's a MicroSOM board specific change, I think.
Ok, that makes a lot of sense. Practical implementation reasons wins any argument. No objections from me to this, I think we understand the reasons now. Iain -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
