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

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Date:   Tue, 4 Aug 2020 09:06:01 +0100
From:   Lukasz Luba <lukasz.luba@....com>
To:     Marek Szyprowski <m.szyprowski@...sung.com>,
        linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-samsung-soc@...r.kernel.org
Cc:     willy.mh.wolff.ml@...il.com, k.konieczny@...sung.com,
        cw00.choi@...sung.com, b.zolnierkie@...sung.com, krzk@...nel.org,
        chanwoo@...nel.org, myungjoo.ham@...sung.com,
        kyungmin.park@...sung.com, s.nawrocki@...sung.com, kgene@...nel.org
Subject: Re: [PATCH v2 2/2] memory: samsung: exynos5422-dmc: Add module param
 to control IRQ mode

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@...il.com>
>>> Signed-off-by: Lukasz Luba <lukasz.luba@....com>
>>
>> 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