Re: [PATCH] memory: samsung: exynos5422-dmc: propagate error from exynos5_counters_get()

From: Marek Szyprowski
Date: Tue Aug 04 2020 - 08:33:30 EST

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@xxxxxxxxxxx>
>> ---
>>   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

> 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