Re: [PATCH] ACPI / platform / LPSS: disable async suspend/resume of LPSS devices

["Li, Aubrey" <aubrey.li@linux.intel.com>]

On 2014/9/26 4:08, Rafael J. Wysocki wrote:
> On Thursday, September 25, 2014 10:07:44 AM Li, Aubrey wrote:
>> On 2014/9/25 4:32, Rafael J. Wysocki wrote:
>>> On Wednesday, September 24, 2014 11:19:22 PM Fu, Zhonghui wrote:
>>>> This is a multi-part message in MIME format.
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>>>>
>>>> On 2014/9/23 7:17, Rafael J. Wysocki wrote:
>>>>> On Monday, September 22, 2014 10:45:42 PM Fu, Zhonghui wrote:
>>>>> [cut]
>>>>>
>>>>>>>>> This operation is reading data from Operation Region of one operand object in name space. I don't know the reason of hang at this point. Could you please give out some explanation about this?
>>>>>>>> I don't know the exact reason why this particular read hangs, but this means
>>>>>>>> that, perhaps, instead of disabling async suspend/resume for all LPSS devices
>>>>>>>> altogether, perhaps we can serialize their acpi_dev_resume_early()?
>>>>>>>>
>>>>>>>> Rafael
>>>>>>> Do you mean keeping other phases(prepare, suspend, suspend_late, suspend_noirq, resume_noirq, resume, complete) of suspend/resume asynchronous, and only serializing "resume_early" phase for all LPSS devices?
>>>>>>>
>>>>>>> Thanks,
>>>>>>> Zhonghui
>>>>>> Hi, Rafael
>>>>>>
>>>>>> Could you please confirm my understanding?
>>>>> This is not what I meant.
>>>>>
>>>>> Since we have a PM domain for the LPSS devices already, why don't we add an
>>>>> internal lock to that PM domain and acquire it over executing either
>>>>> acpi_dev_suspend_late() (during suspend) or acpi_dev_resume_early() (during
>>>>> resume) for all of them?
>>>> I seem find the root cause of this issue. Because this "hang" issue is occurred on ASUS T100(Baytrail-T platform), so I checked its DSDT and found that URT and I2C controllers depend on(_DEP) PEPD device(description in Windows is "power engine plug-in"). That is, URT and I2C controllers can not transition to ACPI_STATE_D0 state until PEPD device has completed this transition during resuming. But, the ACPI subsystem in the 3.16 kernel doesn't support "_DEP" feature. So, if enabling async suspend/resume for LPSS devices, their "_DEP" relationship with PEPD device will be broken and incur "hang" during the transition to ACPI_STATE_D0, please see the following code, it is from dpm_resume_early function in drivers/base/power/main.c file:
>>>>
>>>> list_for_each_entry(dev, &dpm_late_early_list, power.entry) {
>>>>                 reinit_completion(&dev->power.completion);
>>>>                 if (is_async(dev)) {
>>>>                         get_device(dev);
>>>>                         async_schedule(async_resume_early, dev);
>>>>                 }
>>>>         }
>>>>
>>>>         while (!list_empty(&dpm_late_early_list)) {
>>>>                 dev = to_device(dpm_late_early_list.next);
>>>>                 get_device(dev);
>>>>                 list_move_tail(&dev->power.entry, &dpm_suspended_list);
>>>>                 mutex_unlock(&dpm_list_mtx);
>>>>
>>>>                 if (!is_async(dev)) {    // PEPD is not configured as async device now.
>>>>                         int error;
>>>>
>>>>                         error = device_resume_early(dev, state, false);
>>>>                         if (error) {
>>>>                                 suspend_stats.failed_resume_early++;
>>>>                                 dpm_save_failed_step(SUSPEND_RESUME_EARLY);
>>>>                                 dpm_save_failed_dev(dev_name(dev));
>>>>                                 pm_dev_err(dev, state, " early", error);
>>>>                         }
>>>>                 }
>>>>                 mutex_lock(&dpm_list_mtx);
>>>>                 put_device(dev);
>>>>         }
>>>>
>>>>
>>>> Based on the above analysis,I move the resume_early operation of PEPD device to head of dpm_resume_early function and "hang" did not occur any more during resuming(I tested this 10 times).
>>>>
>>>> If disabling async suspend/resume for LPSS devices, PEPD device will be prior to UART and I2C controllers in dpm_late_early_list list and the "_DEP" relationship can be kept. Maybe,the "_DEP" ACPI feature will be supported in future kernel, so, I think simply disabling async suspend/resume for LPSS devices is a acceptable workaround now, and need not add new mechanism to deal with this issue.
>>>>
>>>> BTW, I will take two week's leave and can't reply email during this time. Sorry.
>>>
>>> OK, thanks for the analysis.  In that case we really may be better off by
>>> disabling the runtime PM of LPSS devices for now until we figure out how this
>>> can be addressed properly.
>>
>> Please let me know if the patch need to be refined, I can do it before
>> October 1st, then one-week Chinese National holiday.
> 
> The patch is fine.  In fact, I'm going to push it to Linus shortly.
> 
>> Besides this patch, we leave the non-LPSS devices as async
>> suspend/resume, the risk is unknown.
> 
> No, we don't in general.  That is an opt-in, usually on a per-subsystem basis.
> 
>> I wonder if we need to make
>> pm_async parameter configurable thru kernel command line to make android
>> userspace happy?
> 
> There is a sysfs switch for disabling async suspend/resume (/sys/power/pm_async).
> That has to suffice.
> 
Like what you did to pretend echo mem > /sys/power/state, it's hard to
visit sysfs switch from android UI, we want to disable async
suspend/resume from kernel command line, so that we can bypass this
feature after boot.

Thanks,
-Aubrey