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

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Date:   Mon, 3 Aug 2020 17:35:55 +0200
From:   Marek Szyprowski <m.szyprowski@...sung.com>
To:     Lukasz Luba <lukasz.luba@....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 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
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland