netdev - Re: [drivers/net/phy/sfp] intermittent failure in state machine checks

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Date:   Thu, 9 Jan 2020 23:50:14 +0000
From:   ѽ҉ᶬḳ℠ <vtol@....net>
To:     Russell King - ARM Linux admin <linux@...linux.org.uk>
Cc:     Andrew Lunn <andrew@...n.ch>, netdev@...r.kernel.org
Subject: Re: [drivers/net/phy/sfp] intermittent failure in state machine
 checks


On 09/01/2020 23:10, Russell King - ARM Linux admin wrote:
>
> Please don't use mii-tool with SFPs that do not have a PHY; the "PHY"
> registers are emulated, and are there just for compatibility. Please
> use ethtool in preference, especially for SFPs.

Sure, just ethtool is not much of help for this particular matter, all 
there is ethtool -m and according to you the EEPROM dump is not to be 
relied on.

>
> CONFIG_DEBUG_GPIO is not the same as having debugfs support enabled.
> If debugfs is enabled, then gpiolib will provide the current state
> of gpios through debugfs.  debugfs is normally mounted on
> /sys/kernel/debug, but may not be mounted by default depending on
> policy.  Looking in /proc/filesystems will tell you definitively
> whether debugfs is enabled or not in the kernel.
debugsfs is mounted but ls -af /sys/kernel/debug/gpio only producing 
(oddly):

/sys/kernel/debug/gpio

>
> So, if that is correct...
>
> Current OpenWRT is derived from 4.19-stable kernels, which include
> experimental patches picked at some point from my "phy" branch, and
> TOS is derived from OpenWRT.

This may not be correct since there are not many device targets in 
OpenWrt that feature a SFP cage (least as of today), the Turris Omnia 
might even be the sole one.
I did not check whether that the code was/is available in OpenWrt, and 
likely it is not, but it was in an earlier TOS version since their 
platforms apparently feature a SFP cage.
> That makes it very difficult for anyone in the mainline kernel
> community to do anything about this; sending you a patch is likely
> useless since you're not going to be able to test it.

I understand, I just reached out all the way upstream since other 
available avenues, and started all the way downstream, did not produce 
anything tangible or even a response.
I am grateful that finally at least you obliged and shed some light on 
the matter. Maybe I should just try finding a module that is declared 
SPF MSA conform...

>
> You think the state machines are doing something clever. They don't.
> They are all very simple and quite dumb.

Not really, I assume it just does what it is supposed to do in line with 
current (industry) standards and best practices.

>
> The only real way to get to the bottom of it is to manually enable
> debug in sfp.c so its possible to watch what happens, not only with
> the hardware signals but also what the state machines are doing.
> However, I'm very certain that there is no problem with the state
> machines, and it is that the Allnet module is raising TX_FAULT.

I am sure it does and I am pursuing Allnet for a response, albeit not 
looking promising at the moment. Once there is however I shall pick up 
the thread again.

> I also think from what you've said above that rebuilding a kernel
> to enable debug in sfp.c is going to not be possible for you.

No, I might be able to get this done for amd64 but with this ARM SoC 
there is all kind of other stuff (SPI, MTD, I2C, u-boot and whatnot) 
involved and I am afraid it will go sideways if I attempt compiling.