Hi Florian,

On Thu, Sep 7, 2017 at 3:09 PM, Florian Fainelli [off-list ref] wrote:

On 08/23/2017 10:13 AM, Florian Fainelli wrote:

quoted

On 08/23/2017 04:45 AM, Geert Uytterhoeven wrote:

quoted

On Tue, Aug 22, 2017 at 8:49 PM, Florian Fainelli [off-list ref] wrote:

quoted

On 08/22/2017 11:37 AM, Geert Uytterhoeven wrote:

quoted

If an Ethernet device is used while the device is suspended, the system may
crash.

E.g. on sh73a0/kzm9g and r8a73a4/ape6evm, the external Ethernet chip is
driven by a PM controlled clock.  If the Ethernet registers are accessed
while the clock is not running, the system will crash with an imprecise
external abort.

This patch series fixes two of such crashes:
  1. The first patch prevents the PHY polling state machine from accessing
     PHY registers while a device is suspended,
  2. The second patch prevents the net core from trying to transmit packets
     when an smsc911x device is suspended.

Both crashes can be reproduced on sh73a0/kzm9g and r8a73a4/ape6evm during
s2ram (rarely), or by using pm_test (more likely to trigger):

    # echo 0 > /sys/module/printk/parameters/console_suspend
    # echo platform > /sys/power/pm_test
    # echo mem > /sys/power/state

With this series applied, my test systems survive a loop of 100 test
suspends.

It seems to me like part, if not the entire problem is that smsc91xx's
suspend and resume functions are way too simplistic and absolutely do
not manage the PHY during suspend/resume, the PHY state machine is not
even stopped, so of course, this will cause bus errors if you access
those registers.

You are addressing this as part of patch 2, but this seems to me like
this is still a bit incomplete and you'd need at least phy_stop() and/or
phy_suspend() (does a power down of the PHY) and phy_start() and/or
phy_resume() calls to complete the PHY state machine shutdown during
suspend.

Have you tried that?

Unfortunately that doesn't help.
In state PHY_HALTED, the PHY state machine still calls the .adjust_link()
callback while the device is suspended.

Humm that is correct yes.

quoted

Do you have a clue? This is too far beyond my phy-foo...

I was initially contemplating a revert of
7ad813f208533cebfcc32d3d7474dc1677d1b09a ("net: phy: Correctly process
PHY_HALTED in phy_stop_machine()") but this is not the root of the
problem. The problem really is that phy_stop() does not wait for the PHY
state machine to be stopped so you cannot rely on that and past the
function return be offered any guarantees that adjust_link is not called.

We seem to be getting away with that in most drivers because when we see
phydev->link = 0, we either do nothing or actually turn of the HW block.

How about we export phy_stop_machine() to drivers which would provide a
synchronization point that would ensure that no HW accesses are done
past this point?

I am absolutely not clear on the implications of using a freezable
workqueue with respect to the PHY state machine and how devices are
going to wind-up being powered down or not...

Geert, as you may have notice a revert of the change was sent so 4.13
should be fine, but ultimately I would like to put the non-reverted code
back in after we add a few safeguards:

With the revert, I no longer need "[PATCH 1/2] net: phy: Freeze PHY polling
before suspending devices".
I just did more than 50 successful suspend/resume cycles to verify that.

I still need "[PATCH 2/2] net: smsc911x: Quiten netif during suspend", so
I'll submit a v2 for that.

- and you reported the bus errors on smsc911x when we call adjust_link
during suspend, and due to a lack of hard synchronization so phy_stop()
here does not give you enough guarantees to let you turn off power to
the smsc911x block

If that seems accurate then we can work on something that should be
working again (famous last words).

Sounds accurate to me.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds