On Wed, Jun 17, 2020 at 11:36:42PM +0200, Andrew Lunn wrote:
> On Wed, Jun 17, 2020 at 09:24:50PM +0100, Russell King - ARM Linux admin
> wrote:
> > On Wed, Jun 17, 2020 at 08:43:34PM +0200, Andrew Lunn wrote:
> > > You have explained what the change does. But not why it is
> > > needed. What exactly is happening. To me, the key thing is
> > > understanding why we get -110, and why it is not an actual error we
> > > should be reporting as an error. That is what needs explaining.
> >
> > The patch author really ought to be explaining this... but let me
> > have a go. It's worth pointing out that the comments in the file
> > aren't good English either, so don't really describe what is going
> > on.
> >
> > When this PHY is in EDPD mode, it doesn't always detect a connected
> > cable. The workaround for it involves, when the link is down, and
> > at each read_status() call:
> >
> > - disable EDPD mode, forcing the PHY out of low-power mode
> > - waiting 640ms to see if we have any energy detected from the media
> > - re-enable entry to EDPD mode
> >
> > This is presumably enough to allow the PHY to notice that a cable is
> > connected, and resume normal operations to negotiate with the partner.
> >
> > The problem is that when no media is detected, the 640ms wait times
> > out (as it should, we don't want to wait forever) and the kernel
> > prints a warning.
>
> Hi Russell
>
> Yes, that is what i was thinking.
>
> There probably should be a comment added just to prevent somebody
> swapping it back to phy_read_poll_timeout(). It is not clear that
> -ETIMEOUT is expected under some conditions.
>
> Andrew
Hi Andrew and Russell,
First of all, thanks very much for your comment!
I did not understand Andrew's comments correctly in the previous email,
sorry for my bad English. I found something in the commit 776829de90c597
("net: phy: workaround for buggy cable detection by LAN8700 after cable
plugging") about why it is not an actual error when get a timeout error
in this driver. the commit's link is here:
https://lore.kernel.org/patchwork/patch/590285/
As Russell said, it just for fix a hardware bug on LAN8700 device by wait
640ms, so it should not as an actual error when got timeout.
The following is my understanding:
It leads to unstable detection of plugging in Ethernet cable when LAN87xx
is in Energy Detect Power-Down mode. Because the ENERGYON bit is not set.
For fix this issue, it will disables Energy Detect Power-Down mode and
check ENERGYON bit to waiting for response on link pulses to detect
presence of plugged Ethernet cable in the 640ms. if got the ENERGYON bit
is set, I guess the cable plug-in event was detected and will report an
interrupt after exit lan87xx_read_status() funtion, if the ENERGYON bit
is not set, the plug-in event was not detected. after that, entry Energy
Detect Power-Down mode again.
it will re-call lan87xx_read_status() funtion by interrupt when got the
ENERGYON bit is set. and check link status again. then, It will get a
stable link status for LAN87xx device.
So the timeout for wait 640ms should not as an actual error.
Thanks!
Dejin
