[RFC 1/2] PM / Domains: Power on domain early during system resume

[Krzysztof Kozlowski]

When resuming the system the power domain has to be powered on early so
any runtime PM aware devices could resume.

This fixes following scenario reproduced on Exynos DRM:
1. Power domain is off before suspending the system.
2. System is suspended to RAM.
3. Resuming starts. The Exynos DRM driver resume callback is called.
4. The Exynos DRM driver calls drm_helper_resume_force_mode which turns
   the screen on by calling exynos_dsi_dpms with DRM_MODE_DPMS_ON.
5. The Exynos DSI driver calls pm_runtime_get. The driver runtime
   resumes and this should turn LCD power domain on.
6. Unfortunately the domain cannot be turned on because system resume is
   in progress and genpd->prepared_count is positive.

Steps to reproduce:
1. Add runtime PM to Exynos DSI driver.
2. Build Exynos DRM/FB without FRAMEBUFFER_CONSOLE.
3. Enable the connector and screen (e.g. with modeset-vsync application).
4. echo 3 > /sys/devices/platform/exynos-drm/graphics/fb0/blank
5. echo mem > /sys/power/state
6. Resume.
[   77.712469] PM: early resume of devices complete after 3.854 msecs
[   77.712739] exynos-dsi 11c80000.dsi: pm_genpd_resume()
[   77.712758] exynos4-fimc 11800000.fimc: pm_genpd_resume()
[   77.712774] exynos4-fimc 11810000.fimc: pm_genpd_resume()
[   77.712787] exynos-drm-fimc 11820000.fimc: pm_genpd_resume()
[   77.712802] exynos-drm-fimc 11830000.fimc: pm_genpd_resume()
[   77.712815] s5p-mipi-csis 11880000.csis: pm_genpd_resume()
[   77.712829] s5p-mipi-csis 11890000.csis: pm_genpd_resume()
[   77.712843] exynos-fimc-lite 12390000.fimc-lite: pm_genpd_resume()
[   77.712856] exynos-fimc-lite 123a0000.fimc-lite: pm_genpd_resume()
[   77.713788] exynos4-fb 11c00000.fimd: pm_genpd_resume()
[   77.713912] wake disabled for irq 184
[   77.713923] wake disabled for irq 185
[   77.714082] wake disabled for irq 173
[   77.715676] wake disabled for irq 176
[   77.718540] exynos4-fb 11c00000.fimd: pm_genpd_runtime_resume()
[   77.718567] exynos4-fb 11c00000.fimd: state restore latency exceeded, new value 1708 ns
[   77.718636] exynos-dsi 11c80000.dsi: pm_genpd_runtime_resume()
[   77.892366] exynos-dsi 11c80000.dsi: PLL failed to stabilize
[   77.892377] exynos-dsi 11c80000.dsi: failed to configure DSI PLL
[   78.192168] exynos-dsi 11c80000.dsi: timeout waiting for reset
[   78.211578] exynos-dsi 11c80000.dsi: waiting for bus lanes timed out
[   78.307173] exynos-dsi 11c80000.dsi: xfer timed out: d1 00 (null)
[   78.307190] panel_s6e8aa0 11c80000.dsi.0: error -110 reading dcs seq(0xd1)
[   78.307199] panel_s6e8aa0 11c80000.dsi.0: read id failed

Signed-off-by: Krzysztof Kozlowski <k.kozlowski at samsung.com>
---
 drivers/base/power/domain.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/base/power/domain.c b/drivers/base/power/domain.c
index 40bc2f4072cc..4fdfe404a04c 100644
--- a/drivers/base/power/domain.c
+++ b/drivers/base/power/domain.c
@@ -179,8 +179,7 @@ static int __pm_genpd_poweron(struct generic_pm_domain *genpd)
 	}
 	finish_wait(&genpd->status_wait_queue, &wait);
 
-	if (genpd->status == GPD_STATE_ACTIVE
-	    || (genpd->prepared_count > 0 && genpd->suspend_power_off))
+	if (genpd->status == GPD_STATE_ACTIVE)
 		return 0;
 
 	if (genpd->status != GPD_STATE_POWER_OFF) {
-- 
1.9.1