drm/omap: hdmi4_cec: Fix CEC clock handling for PM

If CONFIG_OMAP4_DSS_HDMI_CEC is enabled in .config, deeper SoC idle
states are blocked because the CEC clock gets always enabled on init.

Let's fix the issue by moving the CEC clock handling to happen later in
hdmi_cec_adap_enable() as suggested by Hans Verkuil <hverkuil@xs4all.nl>.
This way the CEC clock gets only enabled when needed. This can be tested
by doing cec-ctl --playback to enable the CEC, and doing cec-ctl --clear
to disable it.

Let's also fix the typo for "divider" in the comments while at it.

Fixes: 8d7f934 ("omapdrm: hdmi4_cec: add OMAP4 HDMI CEC support")
Suggested-by: Hans Verkuil <hverkuil@xs4all.nl>
Cc: Hans Verkuil <hverkuil@xs4all.nl>
Cc: Jyri Sarha <jsarha@ti.com>
Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>
Reviewed-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190326151438.32414-1-tony@atomide.com

drivers/gpu/drm/omapdrm/dss/hdmi4_cec.c

@@ -175,23 +175,32 @@ static int hdmi_cec_adap_enable(struct cec_adapter *adap, bool enable)
 		REG_FLD_MOD(core->base, HDMI_CORE_SYS_INTR_UNMASK4, 0, 3, 3);
 		hdmi_wp_clear_irqenable(core->wp, HDMI_IRQ_CORE);
 		hdmi_wp_set_irqstatus(core->wp, HDMI_IRQ_CORE);
+		REG_FLD_MOD(core->wp->base, HDMI_WP_CLK, 0, 5, 0);
 		hdmi4_core_disable(core);
 		return 0;
 	}
 	err = hdmi4_core_enable(core);
 	if (err)
 		return err;
 
+	/*
+	 * Initialize CEC clock divider: CEC needs 2MHz clock hence
+	 * set the divider to 24 to get 48/24=2MHz clock
+	 */
+	REG_FLD_MOD(core->wp->base, HDMI_WP_CLK, 0x18, 5, 0);
+
 	/* Clear TX FIFO */
 	if (!hdmi_cec_clear_tx_fifo(adap)) {
 		pr_err("cec-%s: could not clear TX FIFO\n", adap->name);
-		return -EIO;
+		err = -EIO;
+		goto err_disable_clk;
 	}
 
 	/* Clear RX FIFO */
 	if (!hdmi_cec_clear_rx_fifo(adap)) {
 		pr_err("cec-%s: could not clear RX FIFO\n", adap->name);
-		return -EIO;
+		err = -EIO;
+		goto err_disable_clk;
 	}
 
 	/* Clear CEC interrupts */
@@ -236,6 +245,12 @@ static int hdmi_cec_adap_enable(struct cec_adapter *adap, bool enable)
 		hdmi_write_reg(core->base, HDMI_CEC_INT_STATUS_1, temp);
 	}
 	return 0;
+
+err_disable_clk:
+	REG_FLD_MOD(core->wp->base, HDMI_WP_CLK, 0, 5, 0);
+	hdmi4_core_disable(core);
+
+	return err;
 }
 
 static int hdmi_cec_adap_log_addr(struct cec_adapter *adap, u8 log_addr)
@@ -333,11 +348,8 @@ int hdmi4_cec_init(struct platform_device *pdev, struct hdmi_core_data *core,
 		return ret;
 	core->wp = wp;
 
-	/*
-	 * Initialize CEC clock divider: CEC needs 2MHz clock hence
-	 * set the devider to 24 to get 48/24=2MHz clock
-	 */
-	REG_FLD_MOD(core->wp->base, HDMI_WP_CLK, 0x18, 5, 0);
+	/* Disable clock initially, hdmi_cec_adap_enable() manages it */
+	REG_FLD_MOD(core->wp->base, HDMI_WP_CLK, 0, 5, 0);
 
 	ret = cec_register_adapter(core->adap, &pdev->dev);
 	if (ret < 0) {