Re: [PATCH v2 2/2] memory: samsung: exynos5422-dmc: Add module param to control IRQ mode

[Lukasz Luba]

Hi Marek,

On 8/3/20 4:35 PM, Marek Szyprowski wrote:
> Hi All,
>
> On 03.08.2020 17:30, Marek Szyprowski wrote:
> > On 10.07.2020 21:11, Lukasz Luba wrote:
> > > The driver can operate in two modes relaying on devfreq monitoring
> > > mechanism which periodically checks the device status or it can use
> > > interrupts when they are provided by loaded Device Tree. The newly
> > > introduced module parameter can be used to choose between devfreq
> > > monitoring and internal interrupts without modifying the Device Tree.
> > > It also sets devfreq monitoring as default when the parameter is not set
> > > (also the case for default when the driver is not built as a module).
> > >
> > > Reported-by: Willy Wolff <willy.mh.wolff.ml@xxxxxxxxx>
> > > Signed-off-by: Lukasz Luba <lukasz.luba@xxxxxxx>
> >
> > I've got back from my holidays and noticed that in meantime this
> > commit got merged as commit 4fc9a0470d2d. It revealed that there is a
> > race between registering exynos5422-dmc driver and exynos-ppmu driver,
> > which can be observed sometimes as the following message and freeze on
> > Odroid XU3 with multi_v7_defconfig:
> >
> > [    8.767708] exynos5-dmc 10c20000.memory-controller: couldn't probe
> > performance counters
> >
> > I will check this later why the EPROBE_DEFER error is not properly
> > propagated and why it causes a freeze.
>
> It looks that simply propagating return value from
> exynos5_counters_get() in exynos5_dmc_get_status() fixes the boot:
>
> # dmesg | grep dmc
> [    8.838754] exynos-ppmu: new PPMU device registered 10d00000.ppmu
> (ppmu-event3-dmc0_0)
> [    8.861344] exynos-ppmu: new PPMU device registered 10d10000.ppmu
> (ppmu-event3-dmc0_1)
> [    8.868488] exynos5-dmc 10c20000.memory-controller: couldn't probe
> performance counters
> [    8.874417] exynos-ppmu: new PPMU device registered 10d60000.ppmu
> (ppmu-event3-dmc1_0)
> [    8.886612] exynos-ppmu: new PPMU device registered 10d70000.ppmu
> (ppmu-event3-dmc1_1)
> [    9.396769] exynos5-dmc 10c20000.memory-controller: DMC initialized,
> in irq mode: 0
>
> I'm still curious why it freezes if getting performance counters is not
> possible.
>
> Best regards

Thank you for investigating this issue. Indeed, it's odd why it freezes.
I've seen you patch with the fix.

Regards,
Lukasz