Re: [RFC 2/2] net: emac: add support for device-tree based PHY discovery and setup

On 02/14/2017 04:16 PM, Christian Lamparter wrote:

On Tuesday, February 14, 2017 12:38:42 AM CET Christian Lamparter wrote:

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diff --git a/drivers/net/ethernet/ibm/emac/core.c b/drivers/net/ethernet/ibm/emac/core.c
--- a/drivers/net/ethernet/ibm/emac/core.c
+++ b/drivers/net/ethernet/ibm/emac/core.c

@@ -2420,6 +2421,179 @@ static int emac_read_uint_prop(struct device_node *np, const char *name,

[...] 
+static int emac_mii_bus_reset(struct mii_bus *bus)
+{
+	struct emac_instance *dev = netdev_priv(bus->priv);
+
+	emac_mii_reset_phy(&dev->phy);

This seems wrong, emac_mii_reset_phy() does a BMCR software reset, which
PHYLIB is already going to do (phy_init_hw), yet you do this here at the
MDIO bus level towards a specify PHY, whereas this should be affecting
the MDIO bus itself (and/or *all* PHY child devices for quirks).

Ah, this is a good point. The emac driver has a emac_reset() function
that does disable and enabled the phy clocks. That said, this is already
done by the emac driver during init too. So if I added it, the bus is
reset twice (since it doesn't hurt - I added it back).

The emac_mii_phy_reset() was added because of the Meraki MX60(W).
This is because Cisco's bootloader disables the switch port 
(probably to prevent WAN<->LAN leakage during boot)

[bootlog from the MX60(W)]
|Disabling port 0
|Disabling port 1
|Disabling port 2
|Disabling port 3
|ENET Speed is 1000 Mbps - FULL duplex connection (EMAC0)

Without emac_mii_reset_phy(), the mdiobus_scan() function, which
is called by mdiobus_register will fail with -ENODEV.
| /plb/opb/ethernet@ef600c00: failed to attach dt phy (-19).
This is because get_phy_id() will "mostly read mostly Fs" and abort.

Is the PHY just powered down by chance (BMCR_PWRDN set?) and resetting
it implicitly clears the power down that seems to be what is going on.

Yes, the PHY is just in the BMCR_PDOWN state. I can do the same
on the WNDR4700, by messing with u-boot:

| => mii write 0 0 0x0800
| => mii dump
| 0.     (ffff)                 -- PHY control register --
|  (8000:8000) 0.15    =     1    reset
|  (4000:4000) 0.14    =     1    loopback
|  (2040:2040) 0. 6,13 =   b11    speed selection = ??? Mbps
|  (1000:1000) 0.12    =     1    A/N enable
|  (0800:0800) 0.11    =     1    power-down
|  (0400:0400) 0.10    =     1    isolate
|  (0200:0200) 0. 9    =     1    restart A/N
|  (0100:0100) 0. 8    =     1    duplex = full
|  (0080:0080) 0. 7    =     1    collision test enable
|  (003f:003f) 0. 5- 0 =    63    (reserved)

On the Meraki, the port disabled by the bootloader. 
The reset is still needed.

quoted

Keep in mind that MDIO address 16 is the switch's pseudo PHY address
here, so if you are telling PHYLIB to probe for that address and you
don't get the expected MII_PHYSID1/2 value in return, that usually means
that there was a PHY fixup registered to intercept these reads and make
us return the switch's unique identifier. Reading from the switch's
pseudo PHY at address 16 registers 2/3 (MII_PHYSID1/2) is not guaranteed
to return the switch's unique identifer.

With a MDIO device driver this won't happen because you will be probed
by address, and you can read any switch register you want to and from
there move on with the initialization.

quoted

With emac_mii_reset_phy() in place, it gets detected:
| switch0: Atheros AR8327 rev. 4 switch registered on emac_mdio

Furthermore, this is probably not the only device which need it.
Currently, emac's own phy.c code does call emac_mii_reset_phy() 
as well as part of its probe procedure.
<http://lxr.free-electrons.com/source/drivers/net/ethernet/ibm/emac/phy.c#L522>

Ideally, we would like to reset only the ports which are registered in the DT.

Which you would get for free if you did extend qca8k to support the
8327, because qca8k does implicitly tell the DSA layer to register a
dsa_slave_mii_bus which will probe and attach to per-port built-in PHYs
and that happens only for the ports enabled on your specific board.

No, the Meraki and the modified WNDR4700 still refuse to work. Just >one<
of the phys at address 0-4 need to be powered down to get the following
error:
[    4.425618] DSA: switch 0 0 parsed
[    4.429034] DSA: tree 0 parsed
[    4.435416] qca8k: probe of 4ef600c00.ethern:10 failed with error -5

I'll report back, what exactly is causing the error in this case.

Ok, the -EIO error is coming from this line:
<http://lxr.free-electrons.com/source/drivers/net/phy/phy_device.c?v=4.9#L496>

get_phy_id() gets called as part of mdiobus_register() in dsa_ds_apply()
<http://lxr.free-electrons.com/source/net/dsa/dsa2.c?v=4.9#L322> which is
called as part of the dsa_switch_register().

So, is there a good place to reset the switch/ports? Sure,
doing it in qca8k has the advantage that we know it's 5 ports.
However, I'm wondering, if the dsa or phy driver the right
place for this?

Note: behind the mdiobus_read() at 
<http://lxr.free-electrons.com/source/drivers/net/phy/phy_device.c?v=4.9#L494>
is emac's emac_mdio_read does returning -EREMOTEIO. I don't see that hiding
the error code behind a return 0xffff will help much:
---
For example I disabled just phy2:
| Generic PHY 4ef600c00.ethern:00: attached PHY driver [Generic PHY] (mii_bus:phy_addr=4ef600c00.ethern:00, irq=-1)
| Generic PHY dsa-0.0:01: attached PHY driver [Generic PHY] (mii_bus:phy_addr=dsa-0.0:01, irq=-1)
| qca8k 4ef600c00.ethern:10 lan2: no phy at 2
| qca8k 4ef600c00.ethern:10 lan2: failed to connect to phy2: -19
| emac 4ef600c00.ethernet eth0: error -19 setting up slave phy
| qca8k 4ef600c00.ethern:10: Failed to create slave 3: -19
| Generic PHY dsa-0.0:03: attached PHY driver [Generic PHY] (mii_bus:phy_addr=dsa-0.0:03, irq=-1)
| Generic PHY dsa-0.0:04: attached PHY driver [Generic PHY] (mii_bus:phy_addr=dsa-0.0:04, irq=-1)

And as a result: the switch "lost" the port.

When I tried to unbind the "faulty" switch in order to reset it
and rebind:

root@LEDE:/sys/bus/mdio_bus/drivers/qca8k# echo 4ef600c00.ethern:10 > unbind 
[ 2435.970104] Unable to handle kernel paging request for data at address 0x00000050
[ 2435.977580] Faulting instruction address: 0xc0359ae8
[ 2435.982532] Oops: Kernel access of bad area, sig: 11 [#1]
[ 2435.987901] WNDR4700 Platform
[ 2436.116263] CPU: 0 PID: 663 Comm: ash Not tainted 4.9.8 #0
[ 2436.121729] task: cf974000 task.stack: ce42a000
[ 2436.126238] NIP: c0359ae8 LR: c036a534 CTR: c029b338
[ 2436.131180] REGS: ce42bd10 TRAP: 0300   Not tainted  (4.9.8)
[ 2436.136811] MSR: 00029000 <CE,EE,ME>[ 2436.140260]   CR: 24002288  XER: 00000000
[ 2436.144251] DEAR: 00000050 ESR: 00000000 
GPR00: c036a534 ce42bdc0 cf974000 cfb02800 c03f5553 00000000 cf9e19e0 00000001 
GPR08: cf9e1b00 00000040 00000000 00000001 00780100 00000000 00000000 00000000 
GPR16: 00000000 00000000 10060000 1005cf90 b79a2495 1005cf70 b7a354c4 00000000 
GPR24: cfaf2508 00000001 cfaf24fc cfffbca8 cfaf228c 00000003 cfaf2400 cfb02800 
NIP [c0359ae8] dsa_slave_destroy+0x28/0x78
[ 2436.180491] LR [c036a534] dsa_dst_unapply.part.7+0xa4/0xb70
[ 2436.186033] Call Trace:
[ 2436.188475] [ce42bdc0] [c0359c48] dsa_port_is_cpu+0x1c/0x50 (unreliable)
[ 2436.195161] [ce42bdd0] [c036a534] dsa_dst_unapply.part.7+0xa4/0xb70
[ 2436.201409] [ce42be00] [c0359d60] dsa_unregister_switch+0x3c/0x60
[ 2436.207485] [ce42be20] [c0238a18] mdio_remove+0x24/0x40
[ 2436.212701] [ce42be30] [c01c6544] __device_release_driver+0xa4/0x13c
[ 2436.219034] [ce42be40] [c01c6604] device_release_driver+0x28/0x40
[ 2436.225107] [ce42be50] [c01c4c94] unbind_store+0x6c/0xac
[ 2436.230417] [ce42be70] [c00f8838] kernfs_fop_write+0x128/0x1ac
[ 2436.236247] [ce42be90] [c00a8ce4] __vfs_write+0x28/0x134
[ 2436.241542] [ce42bef0] [c00a9a00] vfs_write+0xd0/0x17c
[ 2436.246665] [ce42bf10] [c00aa758] SyS_write+0x4c/0xa4
[ 2436.251705] [ce42bf40] [c000a848] ret_from_syscall+0x0/0x3c
[ 2436.257266] --- interrupt: c01 at 0xb7a0edc0
[ 2436.257266]     LR = 0xb7a00df0
[ 2436.264631] Instruction dump:
[ 2436.267597] 38210030 4e800020 7c0802a6 9421fff0 bfc10008 7c7f1b78 90010014 892304e8 
[ 2436.275397] 814304e4 39290004 55292036 7d2a4a14 <83c90010> 4bf46641 807f04ec 2f830000 
[ 2436.283367] ---[ end trace e5787cb2a55a0fbd ]---
[ 2436.289726] 
[ 2437.291295] Kernel panic - not syncing: Fatal exception

The panic is caused by dsa_slave_create() not clearing the dangling
ds->ports[port].netdev pointer. The function dsa_user_port_unapply()
relies on it being NULL in order to skip unregistered entries.

Fixed that just recently:

https://git.kernel.org/cgit/linux/kernel/git/davem/net-next.git/commit/?id=382e1eea2d983cd2343482c6a638f497bb44a636

and I am currently in the process of making the bind/unbind working
(without having the PHY detached from the network device), but that's a
stretch, and requires a ton of mucking around with driver references,
current state machine state, target state machine state etc...

Candidate patches for that are located here if you want:

https://github.com/ffainelli/linux/commit/e7e99a9ab998952b9f18e6e396779bb58626e9a5
https://github.com/ffainelli/linux/commit/e005be050cd876189f39c5a89fffa70ee8d6c512

-- 
Florian