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Date: Tue, 13 Oct 2020 08:35:54 +0200 From: Thomas Petazzoni <thomas.petazzoni@...tlin.com> To: Ezra Buehler <ezra@...yb.ch> Cc: netdev@...r.kernel.org, Stefan Roese <sr@...x.de>, linux-arm-kernel@...ts.infradead.org, u-boot@...ts.denx.de Subject: Re: Linux mvneta driver unable to read MAC address from HW Hello Ezra, On Sat, 10 Oct 2020 18:41:24 +0200 Ezra Buehler <ezra@...yb.ch> wrote: > I am running Debian buster (Linux 4.19.146) on a Synology DS214+ NAS > (Marvell ARMADA XP). Unfortunately, I end up with random MAC addresses > for the two Ethernet interfaces after boot. (Also with Debian sid, Linux > 5.4.0.) > > Since commit 8cc3e439ab92 ("net: mvneta: read MAC address from hardware > when available") the mvneta Linux driver reads the MVNETA_MAC_ADDR_* > registers when no MAC address is provided by the DT. In my case, only > zeros are read, causing the driver to fall back to a random address. I > was able to verify that the registers are correctly written by the > bootloader by reading out the registers in the U-Boot prompt. > > As a workaround, I now specify the MAC addresses in the DT. However, I > would prefer not to do that. Also, it would be nice to get to the bottom > of this. > > Could it be, that for some reason, the clock of the MAC is removed > either by U-Boot or Linux during boot? I suspect you have the mvneta driver as a module ? If this is the case, then indeed, the MAC address is lost because Linux turns of all unused clocks at the end of the boot. When the driver is built-in, there is a driver adding a reference to the clock before all unused clocks are disabled. When the driver is compiled as a module, this does not happen. So indeed, the correct solution here is to have U-Boot pass the MAC address in the Device Tree. Best regards, Thomas Petazzoni -- Thomas Petazzoni, CTO, Bootlin Embedded Linux and Kernel engineering https://bootlin.com
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