drm: bridge/dw_hdmi: clear i2cmphy_stat0 reg in hdmi_phy_wait_i2c_done

HDMI_IH_I2CMPHY_STAT0 is a clear on write register, which indicates i2cm
operation status(i2c transfer done or error), every hdmi phy register
configuration must check this register to make sure the configuration
has complete. But the indication bit should be cleared after check, otherwise
the corresponding bit will hold on forever, this may give a wrong signal for
next check.

Signed-off-by: Andy Yan <andy.yan@rock-chips.com>
Tested-by: Russell King <rmk+kernel@arm.linux.org.uk>
Acked-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>

drivers/gpu/drm/bridge/dw_hdmi.c

@@ -666,11 +666,15 @@ static inline void hdmi_phy_test_dout(struct dw_hdmi *hdmi,
 
 static bool hdmi_phy_wait_i2c_done(struct dw_hdmi *hdmi, int msec)
 {
-	while ((hdmi_readb(hdmi, HDMI_IH_I2CMPHY_STAT0) & 0x3) == 0) {
+	u32 val;
+
+	while ((val = hdmi_readb(hdmi, HDMI_IH_I2CMPHY_STAT0) & 0x3) == 0) {
 		if (msec-- == 0)
 			return false;
 		udelay(1000);
 	}
+	hdmi_writeb(hdmi, val, HDMI_IH_I2CMPHY_STAT0);
+
 	return true;
 }