check if RGMII works

[Maxim Gorbachyov]

Hello.

I'm trying to use barebox (current git version) with a Freescale
i.MX6q based board. The board is similar to Armadillo 2, but it comes
with another Ethernet PHY. Barebox starts on the board, and there is a
fec_imx0:

barebox at Freescale i.MX6q myboard:/ devinfo fec_imx0
resources:
num   : 0
start : 0x02188000
size  : 0x00001000
driver: fec_imx
no info available for fec_imx0
no parameters available

I've removed AR8031 (Armadillo 2 PHY) code from the mx6_rgmii_rework()
and added these lines:

        for (i = 0; i < 16; ++i) {
                val = mii_read(mdev, mdev->address, i);
                printf("%s() PHY register %d: 0x%04x\n", __FUNCTION__, i, val);
        }

Relevant boot log:

mx6_rgmii_rework() PHY register 0: 0x7fff
mx6_rgmii_rework() PHY register 1: 0xffff
mx6_rgmii_rework() PHY register 2: 0x7fff
mx6_rgmii_rework() PHY register 3: 0xffff
mx6_rgmii_rework() PHY register 4: 0x7fff
mx6_rgmii_rework() PHY register 5: 0xffff
mx6_rgmii_rework() PHY register 6: 0x7fff
mx6_rgmii_rework() PHY register 7: 0xffff
mx6_rgmii_rework() PHY register 8: 0x7fff
mx6_rgmii_rework() PHY register 9: 0xffff
mx6_rgmii_rework() PHY register 10: 0x7fff
mx6_rgmii_rework() PHY register 11: 0xffff
mx6_rgmii_rework() PHY register 12: 0x7fff
mx6_rgmii_rework() PHY register 13: 0xffff
mx6_rgmii_rework() PHY register 14: 0x7fff
mx6_rgmii_rework() PHY register 15: 0xffff

These values are not PHY defaults and actually look strange. I'm not
sure if mii_read() really works here.
Could you please suggest how to check if RGMII communication works?