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

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Date:   Mon, 24 Aug 2020 09:44:56 +0200
From:   Marek Szyprowski <m.szyprowski@...sung.com>
To:     Lukasz Luba <lukasz.luba@....com>,
        Krzysztof Kozlowski <krzk@...nel.org>
Cc:     linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        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,

On 17.08.2020 14:27, Lukasz Luba wrote:
> On 8/17/20 1:07 PM, Krzysztof Kozlowski wrote:
>> On Tue, Aug 04, 2020 at 01:38:11PM +0100, Lukasz Luba wrote:
>>> On 8/4/20 1:19 PM, Marek Szyprowski wrote:
>>>> On 04.08.2020 11:11, Lukasz Luba wrote:
>>>>> 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.
>>>
>>> Really good investigation, great work Marek!
>>>
>>>>
>>>> It looks that the proper fix would be to keep fout_bpll enabled all 
>>>> the
>>>> time.
>>>
>>> Yes, I agree. I am looking for your next patch to test it then.
>>
>> Hi all,
>>
>> Is the patch still useful then? Shall I apply it?
>
> Marek has created different patch for it, which fixes the clock:
> https://lore.kernel.org/linux-clk/20200807133143.22748-1-m.szyprowski@samsung.com/ 
>
>
> So you don't have to apply this one IMO.

Indeed, you can drop this one.

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