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

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Date:   Mon, 17 Aug 2020 13:27:42 +0100
From:   Lukasz Luba <lukasz.luba@....com>
To:     Krzysztof Kozlowski <krzk@...nel.org>
Cc:     Marek Szyprowski <m.szyprowski@...sung.com>,
        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()



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:
>>> 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.
>>
>> 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.

Regards,
Lukasz