ethtool occationally fails to communicate with with ucc_geth

ethtool occationally fails to communicate with with ucc_geth

[Lennart Sorensen]

We are occationally seeing ethtool fail to communicate with ucc_geth.
I think I have tracked down why it happens, but I don't see a good way
to fix it.

When the phy state changes, adjust_link() checks if the state has changed
and if the link is up.  If it is it does:

                if (new_state) {
                        /*
                         * To change the MAC configuration we need to disable
                         * the controller. To do so, we have to either grab
                         * ugeth->lock, which is a bad idea since 'graceful
                         * stop' commands might take quite a while, or we can
                         * quiesce driver's activity.
                         */
                        ugeth_quiesce(ugeth);
                        ugeth_disable(ugeth, COMM_DIR_RX_AND_TX);

                        out_be32(&ug_regs->maccfg2, tempval);
                        out_be32(&uf_regs->upsmr, upsmr);

                        ugeth_enable(ugeth, COMM_DIR_RX_AND_TX);
                        ugeth_activate(ugeth);
                }

The problem I believe is that ugeth_quiesce() does netif_device_detach
which clears __LINK_STATE_PRESENT, and hence makes dev_ethtool fail
due to:

        if (!dev || !netif_device_present(dev))
                return -ENODEV;

So if ethtool happens to be run between ugeth_quiesce() and
ugeth_activate(), it fails as if the device simply doesn't exist, which
is of course not true, it's just temporarily disabled.

I don't see any obvious way to make the ethtool requests block while the
adjust_link does it's business.  It seems that that making the device
disappear is the wrong thing to do though.

I am able to make it happen if I do:

'while ethtool ifname; do :; done' while plugging and unplugging the
cable for a few minutes.

Any suggestions?

-- 
len Sorensen

Re: ethtool occationally fails to communicate with with ucc_geth

[Ben Hutchings]

On Wed, 2013-02-06 at 15:05 -0500, Lennart Sorensen wrote:
> We are occationally seeing ethtool fail to communicate with ucc_geth.
> I think I have tracked down why it happens, but I don't see a good way
> to fix it.
> 
> When the phy state changes, adjust_link() checks if the state has changed
> and if the link is up.  If it is it does:
> 
>                 if (new_state) {
>                         /*
>                          * To change the MAC configuration we need to disable
>                          * the controller. To do so, we have to either grab
>                          * ugeth->lock, which is a bad idea since 'graceful
>                          * stop' commands might take quite a while, or we can
>                          * quiesce driver's activity.
>                          */
>                         ugeth_quiesce(ugeth);
>                         ugeth_disable(ugeth, COMM_DIR_RX_AND_TX);
> 
>                         out_be32(&ug_regs->maccfg2, tempval);
>                         out_be32(&uf_regs->upsmr, upsmr);
> 
>                         ugeth_enable(ugeth, COMM_DIR_RX_AND_TX);
>                         ugeth_activate(ugeth);
>                 }
> 
> The problem I believe is that ugeth_quiesce() does netif_device_detach
> which clears __LINK_STATE_PRESENT, and hence makes dev_ethtool fail
> due to:
> 
>         if (!dev || !netif_device_present(dev))
>                 return -ENODEV;
> 
> So if ethtool happens to be run between ugeth_quiesce() and
> ugeth_activate(), it fails as if the device simply doesn't exist, which
> is of course not true, it's just temporarily disabled.
[...]
> Any suggestions?

This seems to be a workaround for a bug in phylib: phy_state_machine()
calls netif_carrier_on() before adjust_link(), so the TX scheduler can
start immediately even though the MAC has not been configured.

A better workaround would be to use netif_carrier_{off,on}() in
ugeth_{quiesce,activate}() respectively instead of
netif_device_{detach,attach}().  But I think phylib really ought to be
fixed.

Ben.

-- 
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

Re: ethtool occationally fails to communicate with with ucc_geth

[Lennart Sorensen]

On Wed, Feb 06, 2013 at 09:08:32PM +0000, Ben Hutchings wrote:
> This seems to be a workaround for a bug in phylib: phy_state_machine()
> calls netif_carrier_on() before adjust_link(), so the TX scheduler can
> start immediately even though the MAC has not been configured.
> 
> A better workaround would be to use netif_carrier_{off,on}() in
> ugeth_{quiesce,activate}() respectively instead of
> netif_device_{detach,attach}().  But I think phylib really ought to be
> fixed.

I am willing to try things, but this is certainly in parts of the network
stack I don't normally poke around in and hence don't know how works.

I just managed to track it down this far. :)

I can try the carrier_off/on in place of the detach/attach and see if
it works.

-- 
Len Sorensen