Am 2020-04-30 21:38, schrieb Florian Fainelli:
On 4/30/20 12:31 PM, Michael Walle wrote:
Hi Florian,
Am 2020-04-30 20:34, schrieb Florian Fainelli:
On 4/30/20 10:48 AM, Michael Walle wrote:
Hi Andrew,
Am 2020-04-29 18:32, schrieb Andrew Lunn:
On Wed, Apr 29, 2020 at 06:02:13PM +0200, Michael Walle wrote:
Hi Andrew,
> Add infrastructure in ethtool and phylib support for triggering a
> cable test and reporting the results. The Marvell 1G PHY driver is
> then extended to make use of this infrastructure.
I'm currently trying this with the AR8031 PHY. With this PHY, you
have to select the pair which you want to start the test on. So
you'd have to start the test four times in a row for a normal
gigabit cable. Right now, I don't see a way how to do that
efficiently if there is no interrupt. One could start another test
in the get_status() polling if the former was completed
successfully. But then you'd have to wait at least four polling
intervals to get the final result (given a cable with four pairs).
Any other ideas?
Hi Michael
Nice to see some more PHYs getting support for this.
It is important that the start function returns quickly. However,
the
get status function can block. So you could do all the work in the
first call to get status, polling for completion at a faster rate,
etc.
Ok. I do have one problem. TDR works fine for the AR8031 and the
BCM54140 as long as there is no link partner, i.e. open cable,
shorted pairs etc. But as soon as there is a link partner and a
link, both PHYs return garbage. As far as I understand TDR, there
must not be a link, correct? The link partner may send data or
link pulses. No how do you silence the local NIC or even the peer?
Michael do you use the enhanced cable diagnostics (ECD) or the simple
cable diagnostics?
ECD. The registers looks exactly like the one from the Marvell PHYs,
which makes me wonder if both have the same building block or if one
imitated the registers of the other. There are subtle differences
like one bit in the broadcom PHY is "break link" and is self-clearing,
while the bit on the Marvell PHY is described as "perform diagnostics
on link break".
I don't know what simple cable diagnostics should be, I guess the
BCM54140 doesn't support it or its not documented. Actually, ECD
has very little documentation in general.
Yes, there is very little information, even internally. My
understanding
is that diagnostics at run at auto-neg, so you need to break the link,
and when the link comes back up is when you should have per-pair
results. There are also some caveats, like the link parnter must also
have auto-negotiation on for the diagnostics to work.
Ok, that was also my guess.
Having tried to get older Broadcom PHYs to work with
cable diagnostics, you need to calibrate the PHY prior to running
diagnostics and you need to soft reset it.
What do you mean by calibrate it?
You need to tune the AFE and DSP of the PHY in order for it to report
accurate cable lengths. I would not think that you have access to that,
and what I got access to is not really well documented, which is why I
have not had a chance to submit those changes yet.
How accurate are your results when there is no link?
I've only tested with a ~100m cable (or two in a row). The results were
104m to 107m.
-michael
