[PATCH v2 1/2] ARM: kirkwood: Ensure that kirkwood_ge0[01]_init() finds its clock

Simon Baatz gmbnomis at gmail.com
Tue Jan 29 19:03:41 EST 2013

On Tue, Jan 29, 2013 at 09:08:46PM +0100, Sebastian Hesselbarth wrote:
> On 01/29/2013 08:42 PM, Simon Baatz wrote:
> >On Mon, Jan 28, 2013 at 07:48:24PM -0500, Jason Cooper wrote:
> >>On Mon, Jan 28, 2013 at 11:31:48PM +0100, Simon Baatz wrote:
> >>>Nothing special here. My config originally based on a Debian config
> >>>for a Kirkwood kernel.  Thus, amongst other drivers, mv643xx_eth is
> >>>build as a module and is loaded from an initrd.
> >>>Because all relevant drivers are loaded as modules, I need my
> >>>runit patch to boot at all.
> >>
> >>Let's back up.  If you config early printk and COMMON_CLK_DEBUG and a
> >>vanilla v3.8-rc5 with your current config, what happens?
> >
> >I thought it's clear what happens. "runit" is requested in the dts by
> >serial, spi, watchdog, nand, i2c.  Each of these are either not built
> >or built as a module in my config, except serial.
> Simon,
> it is clear what happens but just to blindly disable clock gating will
> not help here. What you are suffering are several issues not only one.

Sure it is more than one issue. That's why I ran different scenarios.

> >of_serial.c does the following in of_platform_serial_setup():
> >
> >	if (of_property_read_u32(np, "clock-frequency",&clk)) {
> >
> >		/* Get clk rate through clk driver if present */
> >		info->clk = clk_get(&ofdev->dev, NULL);
> >		if (IS_ERR(info->clk)) {
> >			dev_warn(&ofdev->dev,
> >				"clk or clock-frequency not defined\n");
> >			return PTR_ERR(info->clk);
> >		}
> >
> >		clk_prepare_enable(info->clk);
> >		clk = clk_get_rate(info->clk);
> >	}
> >
> >and since "clock-frequency" is still given in the standard DTS for
> >the IB-NAS 6210, it does not enable the clock.
> >Thus, no driver uses the clock, it gets disabled and the system locks
> >up.
> >The system boots when removing "clock-frequency" from the DTS.
> >
> >Which lead to two questions:
> >- Is it safe to remove "clock-frequency" now that we have the clocks
> >   in place?
> Safe, as long as you replace it with the corresponding clocks=<&..> property.
> >- The behavior of of_serial.c looks strange to me, is this really the
> >desired behavior?
> I guess it is, rely on clock-frequency because a lot of boards still use it.
> There was no clocks property in of_serial when we started with kirkwood and
> dove. I think we can switch now to clocks property which will also remove
> all hard coded occurrences of tclk frequency.
> >For the "runit" clock, this means that any time you hit a
> >configuration that does not keep the clock enabled, the system will
> >lockup.  (We have gone through this more than once now. Especially,
> >this hits you hard when you try to support a new board and disable as
> >much as possible in the config/dts for a start...).
> Well, if there is no device/driver using runit it should be safe to disable
> it. If there is a driver using it, we need a clocks property for it. And
> as you already stated, serial is using it. And you want serial in every
> minimal kernel, don't you?

>From f479db4:

 Marvell engineers tell us:

 It seems that many units use the RUNIT clock.
 So it's not possible to clock gate it.

 Currently the SPI, NAND and TWSI driver will clk_prepaure_enable()
 this clk, but since we have no idea what ... is, and turning this clk
 off results in a hard lock, unconditionally enable runit.

Thus, if we know better than that, that's fine, but please don't tell
me that this is "blindly" enabling clocks.

> >Thus, we should keep it enabled even if it is unused, which is
> >exactly the purpose of CLK_IGNORE_UNUSED if I understood this
> >correctly.
> True, but only if it is that important that it should _never_ be gated.
> As long as it is 'only' used by peripheral devices, it should be safe
> to gate it.
> >>Could you also please try kirkwood_defconfig and tell us if it boots?
> >
> >It is very easy to get my system to boot with a stock kernel. Just
> >build one of the drivers I use directly into the kernel and it boots
> >(up to the point where the gbe driver is loaded if built as a module,
> >of course).
> >
> >>>Here are my findings with various patches: ("non-DT" means booting
> >>>the IBNAS6210 with machine ID 1680 â??Marvell DB-88F6281-BP
> >>>Development Boardâ??, which works reasonably well)
> >>>
> >>>3.8-rc5 + runit patch:
> >>>
> >>>DT: Hangs at boot (when loading mv643xx_eth)
> >>>non-DT: Boots ok
> >
> >In the DT case ge0 and ge1 are NULL, and thus, kirkwood_ge0[01]_init()
> >tries to enable NULL clocks, but not the gbe clocks. ->  The clocks
> >get disabled.
> >
> >As described in Sebastian's patch (and also found by Andrew some time
> >ago), this leads to a hanging system when loading the gbe driver.
> If I got all your configs right, this DT case is with serial but no
> clocks property? All other runit "users" are _not_ built into the
> kernel? Maybe it is just a coincidence that it fails when loading
> eth but I guess it hangs because of runit getting gated while serial
> accessing it. When you replace serial's clock-frequency with clocks
> property to "runit" it shouldn't hang.

No, this is the SMI hang already. As stated its "3.8-rc5 + runit
patch".  So runit is running.

And sure, removing "clock-frequency" gets the kernel booting until
the gbe driver loads, as I said above in the same mail.

> (Issue 1: gated runit clock hangs kernel due to serial access)

Yes, and issue 1a: gated runit clock hangs kernel due to "...".

I can't get a stock kernel to boot when additionally disabling the
serial driver altogether (and compiling the Ethernet driver into the
kernel to avoid its lockup).

When the runit clock is enabled all the time, it works. I have no
idea where it gets stuck, since I have no console.  It looks like the
SATA module does something (telling from the LEDs), but booting does
not continue.

So, we have a statement from Marvell not to gate it, we know that it
is needed for "...", can we please not gate it?

> >>>3.8-rc5 + runit patch + ge00/ge01 patch:
> >>>
> >>>DT: Boots ok
> >>>non-DT: Boots ok
> >
> >Since the clocks are found now and kept enabled, DT behaves the same
> >as non-DT.
> >
> >>>
> >>>3.8-rc5 + runit + Sebastians get smi clock patch (modified to use
> >>>legacy clock names):
> >>>
> >>>DT: Boots, but no MAC
> >>>non-DT: Boots ok
> >
> >This is the behavior originally found by Andrew. The clock patch
> >eliminates the lockup, but the hardware forgets its MAC address.
> >
> >>>
> >>>3.8-rc5 + runit + using Sebastians patch + clks not ticking at module
> >>>load:
> >>>
> >>>DT: Boots, but no MAC
> >>>non-DT: Boots, but no MAC
> Ok, here my patch for smi clock enables gbe clock before accessing gbe
> registers.
> (Issue 2: gated gbe clock hangs kernel due to smi access)
> >I think non-DT and DT gated clocks behave differently, since the
> >non-DT ones also enable/disable the PHY.  I explicitly removed the
> >clk_prepare_enable() from kirkwood_ge0[01]_init() in order to see if
> >this makes a difference.
> True, DT gated clocks don't disable PHYs (and never will).
> >(Which reminds me, that we wanted to implement the PHY enabling in
> >the driver.)
> >
> >Apparently, it does not make a difference.
> Leaves Issue 3, gbe forgets about its MAC address when gated or powered
> down. That should be done with local-mac-address passed by DT enabled
> u-boot or any other (dirty) ATAG hack ;)

Fine with all of that. But: I am talking about 3.8 all the time. We
have three options for issues 2 and 3 from my point of view:

1. We do proper fixes in 3.8 for issues 2 and 3.

2. We fix this regression by not gating the clock in both the DT and
the non-DT case, preferably by using the correct clocks in
kirkwood_ge0[01]_init().  Additionally, Jason promises that all gets
well with the DT aware driver in 3.9.  ;-)

3. Do nothing. Simply accept that we broke modular Ethernet for DT
because some code relies on two pointers being set.  When we
introduced a new code path for DT, we forgot about these pointers. 
Bad luck, the solution was not nice anyway and we will do proper
fixes in 3.9.

As should be clear by now, I think we should go for option 2.

- Simon

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