Hi Andrew, >From data provided by ASIC engineer, MAC of SP7021 only reads the 4 registers of PHY: 0: Control register 1: Status register 4: Auto-negotiation advertisement register 5: Auto-negotiation link partner ability register It does not read any other registers of PHY. Best regards, Wells Lu > > Hi Andrew, > > > > I set phy-id registers to 30 and 31 and found the read-back values of > > mdio read commands from CPU are all 0x0000. > > > > I consulted with an ASIC engineer. She confirmed that if phy-id of a > > mdio command from CPU does not match any phy-id registers, the mdio > > command will not be sent out. > > > > She explained if phy-id of a mdio command does not match any phy-id > > registers (represent addresses of external PHYs), why MAC needs to > > send a command to non-existing PHY? > > Reads or writes on a real PHY which Linux is driving can have side effects. There is a > link statue register which latches. Read it once, you get the last status, read it again, > you get the current status. If the MAC hardware is reading this register as well a Linux, > bad things will happen. A read on the interrupt status register often clears the interrupts. > So Linux will not see the interrupts. > > So you need to make sure you hardware is not touching a PHY which Linux uses. Which is > why i suggested using MDIO bus address 31, which generally does not have a PHY at that > address. > > Andrew
