linux-kernel - Re: [PATCH 1/5] drm/omap: Fix suspend resume regression after platform data removal

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Date:   Thu, 11 Jun 2020 17:00:59 +0300
From:   Grygorii Strashko <grygorii.strashko@...com>
To:     Tomi Valkeinen <tomi.valkeinen@...com>,
        Tony Lindgren <tony@...mide.com>
CC:     <linux-omap@...r.kernel.org>, "Andrew F . Davis" <afd@...com>,
        Dave Gerlach <d-gerlach@...com>,
        Faiz Abbas <faiz_abbas@...com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Keerthy <j-keerthy@...com>, Nishanth Menon <nm@...com>,
        Peter Ujfalusi <peter.ujfalusi@...com>,
        Roger Quadros <rogerq@...com>, Suman Anna <s-anna@...com>,
        Tero Kristo <t-kristo@...com>, <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <dri-devel@...ts.freedesktop.org>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>
Subject: Re: [PATCH 1/5] drm/omap: Fix suspend resume regression after
 platform data removal



On 09/06/2020 18:26, Tomi Valkeinen wrote:
> On 09/06/2020 18:19, Tony Lindgren wrote:
>>> But there's an extra runtime PM reference (dev.power.usage_count) that seems
>>> to come out of nowhere. So when omap_drm_suspend is finished, there's still
>>> usage_count of 1, and dispc never suspends fully.
>>
>> Hmm no idea about that. My guess is that there might be an issue that was
>> masked earlier with omap_device calling the child runtime_suspend.
> 
> Yes. It's how PM works. It calls pm_runtime_get_noresume() before starting the suspend of a device. So I guess omapdrm's suspend has been broken all the time, but it was "fixed" by omap_device.
> 

I think I might have an idea what is going wrong.

Before:
+----------------------+
|omap_device_pm_domain |
+---------------+------+------+
                 | device      |
                 +-------------+
                 | omap_device |
                 +-------------+

omap_device is embedded in DD device and PM handled by omap_device_pm_domain.

static int _od_suspend_noirq(struct device *dev)
{
...

	ret = pm_generic_suspend_noirq(dev);
[1] ^^ device suspend_noirq call

	if (!ret && !pm_runtime_status_suspended(dev)) {
		if (pm_generic_runtime_suspend(dev) == 0) {
[2] ^^ device pm_runtime_suspend force call

			omap_device_idle(pdev);
[3] ^^ omap_device disable
			od->flags |= OMAP_DEVICE_SUSPENDED;
		}
	}

	return ret;
}

Now:
+------------+
|ti sysc dev |
+-+----------+
   |
   |
   |   +-------------+
   |   | device      |
   +-->+             |
       +-------------+

With new approach the omap_device is not embedded in DD Device anymore,
instead ti-sysc (hwmod replacement) became parent of DD Device.

As result suspend sequence became the following
(Note. All PM runtime PUT calls became NOP during suspend by design):

device
|-> suspend() - in case of dss omap_drm_suspend() and Co if defined
|-> suspend_noirq() - in case of dss *not defined", equal to step [1] above
..

ti sysc dev (ti-sysc is parent, so called after device)
|-> sysc_noirq_suspend
    |-> pm_runtime_force_suspend()
	|-> sysc_runtime_suspend() - equal to step [3] above

And step [2] is missing as of now!

I think, suspend might be fixed if all devices, which are now child of ti-sysc, will do
pm_runtime_force_xxx() calls at noirq suspend stage by adding:

	SET_NOIRQ_SYSTEM_SLEEP_PM_OPS(pm_runtime_force_suspend,
				      pm_runtime_force_resume)

Am I missing smth?

-- 
Best regards,
grygorii