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Date: Fri, 1 Apr 2022 08:40:06 +0200 From: Oleksij Rempel <o.rempel@...gutronix.de> To: Andrew Lunn <andrew@...n.ch> Cc: "huangguangbin (A)" <huangguangbin2@...wei.com>, davem@...emloft.net, kuba@...nel.org, netdev@...r.kernel.org, linux-kernel@...r.kernel.org, lipeng321@...wei.com, chenhao288@...ilicon.com Subject: Re: [PATCH] net: phy: genphy_loopback: fix loopback failed when speed is unknown On Thu, Mar 31, 2022 at 04:26:47PM +0200, Andrew Lunn wrote: > > In this case, as speed and duplex both are unknown, ctl is just set to 0x4000. > > However, the follow code sets mask to ~0 for function phy_modify(): > > int genphy_loopback(struct phy_device *phydev, bool enable) > > { > > if (enable) { > > ... > > phy_modify(phydev, MII_BMCR, ~0, ctl); > > ... > > } > > so all other bits of BMCR will be cleared and just set bit 14, I use phy trace to > > prove that: > > > > $ cat /sys/kernel/debug/tracing/trace > > # tracer: nop > > # > > # entries-in-buffer/entries-written: 923/923 #P:128 > > # > > # _-----=> irqs-off/BH-disabled > > # / _----=> need-resched > > # | / _---=> hardirq/softirq > > # || / _--=> preempt-depth > > # ||| / _-=> migrate-disable > > # |||| / delay > > # TASK-PID CPU# ||||| TIMESTAMP FUNCTION > > # | | | ||||| | | > > kworker/u257:2-694 [015] ..... 209.263912: mdio_access: mii-0000:bd:00.1 read phy:0x03 reg:0x00 val:0x1040 > > kworker/u257:2-694 [015] ..... 209.263951: mdio_access: mii-0000:bd:00.1 read phy:0x03 reg:0x01 val:0x7989 > > kworker/u257:2-694 [015] ..... 209.263990: mdio_access: mii-0000:bd:00.1 read phy:0x03 reg:0x01 val:0x7989 > > kworker/u257:2-694 [015] ..... 209.264028: mdio_access: mii-0000:bd:00.1 read phy:0x03 reg:0x09 val:0x0200 > > kworker/u257:2-694 [015] ..... 209.264067: mdio_access: mii-0000:bd:00.1 read phy:0x03 reg:0x0a val:0x0000 > > ethtool-1148 [007] ..... 209.665693: mdio_access: mii-0000:bd:00.1 read phy:0x03 reg:0x00 val:0x1040 > > ethtool-1148 [007] ..... 209.665706: mdio_access: mii-0000:bd:00.1 write phy:0x03 reg:0x00 val:0x1840 > > ethtool-1148 [007] ..... 210.588139: mdio_access: mii-0000:bd:00.1 read phy:0x03 reg:0x00 val:0x1840 > > ethtool-1148 [007] ..... 210.588152: mdio_access: mii-0000:bd:00.1 write phy:0x03 reg:0x00 val:0x1040 > > ethtool-1148 [007] ..... 210.615900: mdio_access: mii-0000:bd:00.1 read phy:0x03 reg:0x00 val:0x1040 > > ethtool-1148 [007] ..... 210.615912: mdio_access: mii-0000:bd:00.1 write phy:0x03 reg:0x00 val:0x4000 //here just set bit 14 > > > > So phy speed will be set to 10M in this case, if previous speed of > > device before going down is 10M, loopback test is pass. Only > > previous speed is 100M or 1000M, loopback test is failed. > > O.K. So it should be set into 10M half duplex. But why does this cause > it not to loopback packets? Does the PHY you are using not actually > support 10 Half? Why does it need to be the same speed as when the > link was up? And why does it actually set LSTATUS indicating there is > link? > > Is this a generic problem, all PHYs are like this, or is this specific > to the PHY you are using? Maybe this PHY needs its own loopback > function because it does something odd? It looks for me like attempt to fix loopback test for setup without active link partner. Correct? Regards, Oleksij -- Pengutronix e.K. | | Steuerwalder Str. 21 | http://www.pengutronix.de/ | 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |
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