linux-kernel - Re: [PATCH] memory: samsung: exynos5422-dmc: propagate error from exynos5_counters

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Message-ID: <78c95f58-8142-7607-6d74-5cfa6a7ffb77@samsung.com>
Date:   Tue, 4 Aug 2020 14:19:25 +0200
From:   Marek Szyprowski <m.szyprowski@...sung.com>
To:     Lukasz Luba <lukasz.luba@....com>, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org
Cc:     Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        linux-samsung-soc@...r.kernel.org,
        Chanwoo Choi <cw00.choi@...sung.com>
Subject: Re: [PATCH] memory: samsung: exynos5422-dmc: propagate error from
 exynos5_counters_get()

Hi Lukasz,

On 04.08.2020 11:11, Lukasz Luba wrote:
> Hi Marek,
>
> On 8/4/20 7:12 AM, Marek Szyprowski wrote:
>> exynos5_counters_get() might fail with -EPROBE_DEFER if the driver for
>> devfreq event counter is not yet probed. Propagate that error value to
>> the caller to ensure that the exynos5422-dmc driver will be probed again
>> when devfreq event contuner is available.
>>
>> This fixes boot hang if both exynos5422-dmc and exynos-ppmu drivers are
>> compiled as modules.
>>
>> Signed-off-by: Marek Szyprowski <m.szyprowski@...sung.com>
>> ---
>>   drivers/memory/samsung/exynos5422-dmc.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/memory/samsung/exynos5422-dmc.c 
>> b/drivers/memory/samsung/exynos5422-dmc.c
>> index b9c7956e5031..639811a3eecb 100644
>> --- a/drivers/memory/samsung/exynos5422-dmc.c
>> +++ b/drivers/memory/samsung/exynos5422-dmc.c
>> @@ -914,7 +914,7 @@ static int exynos5_dmc_get_status(struct device 
>> *dev,
>>       } else {
>>           ret = exynos5_counters_get(dmc, &load, &total);
>>           if (ret < 0)
>> -            return -EINVAL;
>> +            return ret;
>>             /* To protect from overflow, divide by 1024 */
>>           stat->busy_time = load >> 10;
>>
>
> Thank you for the patch, LGTM.
> Some questions are still there, though. The function
> exynos5_performance_counters_init() should capture that the counters
> couldn't be enabled or set. So the functions:
> exynos5_counters_enable_edev() and exynos5_counters_set_event()
> must pass gently because devfreq device is registered.
> Then devfreq checks device status, and reaches the state when
> counters 'get' function returns that they are not ready...
>
> If that is a kind of 2-stage initialization, maybe we should add
> another 'check' in the exynos5_performance_counters_init() and call
> the devfreq_event_get_event() to make sure that we are ready to go,
> otherwise return ret from that function (which is probably EPROBE_DEFER)
> and not register the devfreq device.

I've finally investigated this further and it turned out that the issue 
is elsewhere. The $subject patch can be discarded, as it doesn't fix 
anything. The -EPROBE_DEFER is properly returned by 
exynos5_performance_counters_init(), which redirects exynos5_dmc_probe() 
to remove_clocks label. This causes disabling mout_bpll/fout_bpll clocks 
what in turn *sometimes* causes boot hang. This random behavior mislead 
me that the $subject patch fixes the issue, but then longer tests 
revealed that it didn't change anything.

It looks that the proper fix would be to keep fout_bpll enabled all the 
time.

>
> Marek do want to submit such patch or I should bake it and submit on top
> of this patch?
>
> Could you tell me how I can reproduce this? Do you simply load one
> module after another (exynos-ppmu than exynos5422-dmc) or in parallel?

I've just boot zImage built from multi_v7_defconfig with modules 
installed. Modules are automatically loaded by udev during boot.

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland