[PATCHv2] drm/omap: Fix issue with clocks left on after resume

[Tony Lindgren <tony@atomide.com>]

On resume, dispc pm_runtime_force_resume() is not enabling the hardware
as we pass the pm_runtime_need_not_resume() test as the device is suspended
with no child devices.

As the resume continues, omap_atomic_comit_tail() calls dispc_runtime_get()
that calls rpm_resume() enabling the hardware, and increasing child_count
for it's parent device.

But at this point device_complete() has not yet been called for dispc. So
when omap_atomic_comit_tail() calls dispc_runtime_put(), it won't idle
the hardware as rpm_suspend() returns -EBUSY, and the clocks are left on
after resume. The parent child count is not decremented as the -EBUSY
cannot be easily handled until later on after device_complete().

This can be easily seen for example after suspending Beagleboard-X15 with
no displays connected, and by reading the CM_DSS_DSS_CLKCTRL register at
0x4a009120 after resume. After a suspend and resume cycle, it shows a
value of 0x00040102 instead of 0x00070000 like it should.

Let's fix the issue by calling dispc_runtime_suspend() and
dispc_runtime_resume() directly from dispc_suspend() and dispc_resume().
This leaves out the PM runtime related issues for system suspend.

We could handle the issue by adding more calls to dispc_runtime_get()
and dispc_runtime_put() from omap_drm_suspend() and omap_drm_resume()
as suggested by Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>.
But that would just add more inter-component calls and more dependencies
to PM runtime for system suspend and does not make things easier in the
long.

See also earlier commit 88d26136a256 ("PM: Prevent runtime suspend during
system resume") and commit ca8199f13498 ("drm/msm/dpu: ensure device
suspend happens during PM sleep") for more information.

Fixes: ecfdedd7da5d ("drm/omap: force runtime PM suspend on system suspend")
Signed-off-by: Tony Lindgren <tony@atomide.com>
---

Changes since v1:
- Updated the description for a typo noticed by Tomi
- Added more info about what all goes wrong

---
 drivers/gpu/drm/omapdrm/dss/dispc.c | 27 ++++++++++++++++++++++++++-
 1 file changed, 26 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/omapdrm/dss/dispc.c b/drivers/gpu/drm/omapdrm/dss/dispc.c
--- a/drivers/gpu/drm/omapdrm/dss/dispc.c
+++ b/drivers/gpu/drm/omapdrm/dss/dispc.c
@@ -182,6 +182,7 @@ struct dispc_device {
 	const struct dispc_features *feat;
 
 	bool is_enabled;
+	bool needs_resume;
 
 	struct regmap *syscon_pol;
 	u32 syscon_pol_offset;
@@ -4887,10 +4888,34 @@ static int dispc_runtime_resume(struct device *dev)
 	return 0;
 }
 
+static int dispc_suspend(struct device *dev)
+{
+	struct dispc_device *dispc = dev_get_drvdata(dev);
+
+	if (!dispc->is_enabled)
+		return 0;
+
+	dispc->needs_resume = true;
+
+	return dispc_runtime_suspend(dev);
+}
+
+static int dispc_resume(struct device *dev)
+{
+	struct dispc_device *dispc = dev_get_drvdata(dev);
+
+	if (!dispc->needs_resume)
+		return 0;
+
+	dispc->needs_resume = false;
+
+	return dispc_runtime_resume(dev);
+}
+
 static const struct dev_pm_ops dispc_pm_ops = {
 	.runtime_suspend = dispc_runtime_suspend,
 	.runtime_resume = dispc_runtime_resume,
-	SET_LATE_SYSTEM_SLEEP_PM_OPS(pm_runtime_force_suspend, pm_runtime_force_resume)
+	SET_LATE_SYSTEM_SLEEP_PM_OPS(dispc_suspend, dispc_resume)
 };
 
 struct platform_driver omap_dispchw_driver = {
-- 
2.31.1
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