[PATCH] drm/lcdif: Do not disable clock on already suspended hardware

[Marek Vasut]

In case the LCDIF is enabled in DT but unused, the clock used by the
LCDIF are not enabled. Those clock may even have a use count of 0 in
case there are no other users of those clock. This can happen e.g. in
case the LCDIF drives HDMI bridge which has no panel plugged into the
HDMI connector.

Do not attempt to disable clock in the suspend callback and re-enable
clock in the resume callback unless the LCDIF is enabled and was in
use before the system entered suspend, otherwise the driver might end
up trying to disable clock which are already disabled with use count
0, and would trigger a warning from clock core about this condition.

Note that the lcdif_rpm_suspend() and lcdif_rpm_resume() functions
internally perform the clock disable and enable operations and act
as runtime PM hooks too.

Fixes: 9db35bb349a0 ("drm: lcdif: Add support for i.MX8MP LCDIF variant")
Signed-off-by: Marek Vasut <marex at denx.de>
---
Cc: Daniel Vetter <daniel at ffwll.ch>
Cc: David Airlie <airlied at gmail.com>
Cc: Fabio Estevam <festevam at gmail.com>
Cc: Liu Ying <victor.liu at nxp.com>
Cc: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
Cc: Maxime Ripard <mripard at kernel.org>
Cc: NXP Linux Team <linux-imx at nxp.com>
Cc: Pengutronix Kernel Team <kernel at pengutronix.de>
Cc: Sascha Hauer <s.hauer at pengutronix.de>
Cc: Shawn Guo <shawnguo at kernel.org>
Cc: Stefan Agner <stefan at agner.ch>
Cc: Thomas Zimmermann <tzimmermann at suse.de>
Cc: dri-devel at lists.freedesktop.org
Cc: linux-arm-kernel at lists.infradead.org
---
 drivers/gpu/drm/mxsfb/lcdif_drv.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/mxsfb/lcdif_drv.c b/drivers/gpu/drm/mxsfb/lcdif_drv.c
index ea10bf81582e9..0f895b8a99d62 100644
--- a/drivers/gpu/drm/mxsfb/lcdif_drv.c
+++ b/drivers/gpu/drm/mxsfb/lcdif_drv.c
@@ -343,6 +343,9 @@ static int __maybe_unused lcdif_suspend(struct device *dev)
 	if (ret)
 		return ret;
 
+	if (pm_runtime_suspended(dev))
+		return 0;
+
 	return lcdif_rpm_suspend(dev);
 }
 
@@ -350,7 +353,8 @@ static int __maybe_unused lcdif_resume(struct device *dev)
 {
 	struct drm_device *drm = dev_get_drvdata(dev);
 
-	lcdif_rpm_resume(dev);
+	if (!pm_runtime_suspended(dev))
+		lcdif_rpm_resume(dev);
 
 	return drm_mode_config_helper_resume(drm);
 }
-- 
2.43.0