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

From: Rafael J. Wysocki
Date: Fri Sep 26 2014 - 09:46:50 EST

On Friday, September 26, 2014 11:54:42 AM Li, Aubrey wrote:
> 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.
> >>>> --------------040808000309050202010005
> >>>> Content-Type: text/plain; charset=UTF-8
> >>>> Content-Transfer-Encoding: 7bit
> >>>>
> >>>>
> >>>> 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,

That was supposed to be an exception.

> 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.

Please feel free to submit a patch adding a command line switch to set the
initial value of /sys/power/pm_async. Maybe people won't complain about it.

Rafael

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