[PATCH] drm/stm: repair runtime power management

[Marek Vasut <marex@denx.de>]

Add missing pm_runtime_get_sync() into ltdc_crtc_atomic_enable() to
match pm_runtime_put_sync() in ltdc_crtc_atomic_disable(), otherwise
the LTDC might suspend via runtime PM, disable clock, and then fail
to resume later on.

The test which triggers it is roughly -- run qt5 application which
uses eglfs platform and etnaviv, stop the application, sleep for 15
minutes, run the application again. This leads to a timeout waiting
for vsync, because the LTDC has suspended, but did not resume.

Fixes: 35ab6cfbf211 ("drm/stm: support runtime power management")
Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Yannick Fertré <yannick.fertre@st.com>
Cc: Philippe Cornu <philippe.cornu@st.com>
Cc: Benjamin Gaignard <benjamin.gaignard@linaro.org>
Cc: Vincent Abriou <vincent.abriou@st.com>
Cc: Maxime Coquelin <mcoquelin.stm32@gmail.com>
Cc: Alexandre Torgue <alexandre.torgue@st.com>
To: dri-devel@lists.freedesktop.org
Cc: linux-stm32@st-md-mailman.stormreply.com
Cc: linux-arm-kernel@lists.infradead.org
---
------------[ cut here ]------------
WARNING: CPU: 0 PID: 297 at drivers/gpu/drm/drm_atomic_helper.c:1494 drm_atomic_helper_wait_for_vblanks+0x1dc/0x200
[CRTC:35:crtc-0] vblank wait timed out
Modules linked in:
CPU: 0 PID: 297 Comm: QSGRenderThread Not tainted 5.6.0-rc3-next-20200228-00010-g318bf0fc08ef #2
Hardware name: STM32 (Device Tree Support)
[<c010f18c>] (unwind_backtrace) from [<c010afb8>] (show_stack+0x10/0x14)
[<c010afb8>] (show_stack) from [<c07b1d3c>] (dump_stack+0xb4/0xd0)
[<c07b1d3c>] (dump_stack) from [<c011d8b8>] (__warn+0xd4/0xf0)
[<c011d8b8>] (__warn) from [<c011dc4c>] (warn_slowpath_fmt+0x78/0xa8)
[<c011dc4c>] (warn_slowpath_fmt) from [<c04a266c>] (drm_atomic_helper_wait_for_vblanks+0x1dc/0x200)
[<c04a266c>] (drm_atomic_helper_wait_for_vblanks) from [<c04a510c>] (drm_atomic_helper_commit_tail+0
x50/0x60)
[<c04a510c>] (drm_atomic_helper_commit_tail) from [<c04a52a8>] (commit_tail+0x12c/0x13c)
[<c04a52a8>] (commit_tail) from [<c04a53b4>] (drm_atomic_helper_commit+0xf4/0x100)
[<c04a53b4>] (drm_atomic_helper_commit) from [<c04a2d38>] (drm_atomic_helper_set_config+0x58/0x6c)
[<c04a2d38>] (drm_atomic_helper_set_config) from [<c04b1994>] (drm_mode_setcrtc+0x450/0x550)
[<c04b1994>] (drm_mode_setcrtc) from [<c04ad570>] (drm_ioctl_kernel+0x90/0xe8)
[<c04ad570>] (drm_ioctl_kernel) from [<c04ad8ac>] (drm_ioctl+0x2e4/0x32c)
[<c04ad8ac>] (drm_ioctl) from [<c0246784>] (vfs_ioctl+0x20/0x38)
[<c0246784>] (vfs_ioctl) from [<c02470f0>] (ksys_ioctl+0xbc/0x7b0)
[<c02470f0>] (ksys_ioctl) from [<c0101000>] (ret_fast_syscall+0x0/0x54)
Exception stack(0xee8f3fa8 to 0xee8f3ff0)
3fa0:                   00000005 adcbeb18 00000005 c06864a2 adcbeb18 00000001
3fc0: 00000005 adcbeb18 c06864a2 00000036 00000029 00000023 00000023 00000007
3fe0: b113b098 adcbeafc b1125413 b6155cf8
---[ end trace 2ad5ba954ceb767a ]---
---
 drivers/gpu/drm/stm/ltdc.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/gpu/drm/stm/ltdc.c b/drivers/gpu/drm/stm/ltdc.c
index 99bf93e8b36f..301de0498078 100644
--- a/drivers/gpu/drm/stm/ltdc.c
+++ b/drivers/gpu/drm/stm/ltdc.c
@@ -425,9 +425,12 @@ static void ltdc_crtc_atomic_enable(struct drm_crtc *crtc,
 				    struct drm_crtc_state *old_state)
 {
 	struct ltdc_device *ldev = crtc_to_ltdc(crtc);
+	struct drm_device *ddev = crtc->dev;
 
 	DRM_DEBUG_DRIVER("\n");
 
+	pm_runtime_get_sync(ddev->dev);
+
 	/* Sets the background color value */
 	reg_write(ldev->regs, LTDC_BCCR, BCCR_BCBLACK);
 
-- 
2.25.0


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