[PATCH v4 1/2] drm/imx/lcdc: avoid duplicate clk_per enable

[Ze Huang]

The simple-KMS helper calls the pipe update after enabling the CRTC.
On an enable commit, imx_lcdc_pipe_enable() already programs the
mode and enables clk_per. The following pipe update sees the plane move
from no CRTC to the active CRTC, treats it as a mode update, and calls
imx_lcdc_update_hw_registers() again.

That second call has no old CRTC state to disable clk_per first, but it
enables clk_per again at the end. The disable path only drops one
reference, leaving clk_per enabled after each on/off cycle.

Skip the register update from the pipe update path when the CRTC already
needs a modeset. The enable path has already programmed the hardware for
that commit; keep the event handling in pipe update unchanged.

Fixes: c87e859cdeb5 ("drm/imx/lcdc: Implement DRM driver for imx25")
Acked-by: Thomas Zimmermann <tzimmermann at suse.de>
Signed-off-by: Ze Huang <ze.huang at oss.qualcomm.com>
---
 drivers/gpu/drm/imx/lcdc/imx-lcdc.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/imx/lcdc/imx-lcdc.c b/drivers/gpu/drm/imx/lcdc/imx-lcdc.c
index c67fe80b8115..e00e52c1c46e 100644
--- a/drivers/gpu/drm/imx/lcdc/imx-lcdc.c
+++ b/drivers/gpu/drm/imx/lcdc/imx-lcdc.c
@@ -310,7 +310,8 @@ static void imx_lcdc_pipe_update(struct drm_simple_display_pipe *pipe,
 	else if (old_crtc != crtc)
 		mode_changed = true;
 
-	imx_lcdc_update_hw_registers(pipe, old_state, mode_changed);
+	if (!drm_atomic_crtc_needs_modeset(crtc->state))
+		imx_lcdc_update_hw_registers(pipe, old_state, mode_changed);
 
 	if (event) {
 		crtc->state->event = NULL;

-- 
2.55.0