[PATCH] drm/panfrost: Unprepare clocks on system suspend

[Michał Kopeć]

With GPU_PM_CLK_DIS, system suspend only disables the GPU clocks, which
leaves them prepared. Some providers power a clock down only in
unprepare: MediaTek PLLs are switched off in mtk_pll_unprepare(). On
MT8188 this keeps MFGPLL running through suspend, and TF-A refuses the
26 MHz-off state because of it:

  suspend: bus26m total blocked = 0x40040000

The SoC then only reaches a shallower sleep state, never signals sleep
to the EC, and the EC reports a sleep hang and wakes the system.

Use clk_disable_unprepare() on suspend and clk_prepare_enable() on
resume. Both run in process context, so preparing is allowed.

Fixes: 56e76c017918 ("drm/panfrost: Implement ability to turn on/off GPU clocks 
in suspend")
Signed-off-by: Michał Kopeć <michal@nozomi.space>
---
 drivers/gpu/drm/panfrost/panfrost_device.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/panfrost/panfrost_device.c 
b/drivers/gpu/drm/panfrost/panfrost_device.c
index 485349faf2511..3f1a8109a79a4 100644
--- a/drivers/gpu/drm/panfrost/panfrost_device.c
+++ b/drivers/gpu/drm/panfrost/panfrost_device.c
@@ -507,12 +507,12 @@ static int panfrost_device_resume(struct device *dev)
        }
 
        if (pfdev->comp->pm_features & BIT(GPU_PM_CLK_DIS)) {
-               ret = clk_enable(pfdev->clock);
+               ret = clk_prepare_enable(pfdev->clock);
                if (ret)
                        goto err_clk;
 
                if (pfdev->bus_clock) {
-                       ret = clk_enable(pfdev->bus_clock);
+                       ret = clk_prepare_enable(pfdev->bus_clock);
                        if (ret)
                                goto err_bus_clk;
                }
@@ -526,10 +526,10 @@ static int panfrost_device_resume(struct device *dev)
 
 err_resume:
        if (pfdev->comp->pm_features & BIT(GPU_PM_CLK_DIS) && pfdev->bus_clock)
-               clk_disable(pfdev->bus_clock);
+               clk_disable_unprepare(pfdev->bus_clock);
 err_bus_clk:
        if (pfdev->comp->pm_features & BIT(GPU_PM_CLK_DIS))
-               clk_disable(pfdev->clock);
+               clk_disable_unprepare(pfdev->clock);
 err_clk:
        if (pfdev->comp->pm_features & BIT(GPU_PM_VREG_OFF))
                dev_pm_opp_set_opp(dev, NULL);
@@ -545,11 +545,15 @@ static int panfrost_device_suspend(struct device *dev)
        if (ret)
                return ret;
 
+       /*
+        * Unprepare as well: some clock providers, e.g. MediaTek PLLs, only
+        * power down in unprepare, and a running GPU PLL blocks system sleep.
+        */
        if (pfdev->comp->pm_features & BIT(GPU_PM_CLK_DIS)) {
                if (pfdev->bus_clock)
-                       clk_disable(pfdev->bus_clock);
+                       clk_disable_unprepare(pfdev->bus_clock);
 
-               clk_disable(pfdev->clock);
+               clk_disable_unprepare(pfdev->clock);
        }
 
        if (pfdev->comp->pm_features & BIT(GPU_PM_VREG_OFF))

base-commit: 70456f05d4b6396b22048c4b8cd3cb98ecf9f9e3
-- 
2.55.0