drm: bridge: dw-hdmi: Handle overflow workaround based on device version

Use the device version queried at runtime instead of the device type
provided through platform data to handle the overflow workaround. This
will make support of other SoCs integrating the same HDMI TX controller
version easier.

Among the supported platforms only i.MX6DL and i.MX6Q have been
identified as needing the workaround. Disabling it on Rockchip RK3288
(which integrates a v2.00a controller) didn't produce any error or
artifact.
Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Reviewed-by: Jose Abreu <joabreu@synopsys.com>
Signed-off-by: Archit Taneja <architt@codeaurora.org>
Link: http://patchwork.freedesktop.org/patch/msgid/20170117082910.27023-16-laurent.pinchart+renesas@ideasonboard.com

drivers/gpu/drm/bridge/dw-hdmi.c

@@ -117,8 +117,10 @@ struct dw_hdmi {
 	struct drm_connector connector;
 	struct drm_bridge bridge;
 
-	struct platform_device *audio;
 	enum dw_hdmi_devtype dev_type;
+	unsigned int version;
+
+	struct platform_device *audio;
 	struct device *dev;
 	struct clk *isfr_clk;
 	struct clk *iahb_clk;
@@ -1323,19 +1325,38 @@ static void hdmi_enable_audio_clk(struct dw_hdmi *hdmi)
 /* Workaround to clear the overflow condition */
 static void dw_hdmi_clear_overflow(struct dw_hdmi *hdmi)
 {
-	int count;
+	unsigned int count;
+	unsigned int i;
 	u8 val;
 
-	/* TMDS software reset */
-	hdmi_writeb(hdmi, (u8)~HDMI_MC_SWRSTZ_TMDSSWRST_REQ, HDMI_MC_SWRSTZ);
+	/*
+	 * Under some circumstances the Frame Composer arithmetic unit can miss
+	 * an FC register write due to being busy processing the previous one.
+	 * The issue can be worked around by issuing a TMDS software reset and
+	 * then write one of the FC registers several times.
+	 *
+	 * The number of iterations matters and depends on the HDMI TX revision
+	 * (and possibly on the platform). So far only i.MX6Q (v1.30a) and
+	 * i.MX6DL (v1.31a) have been identified as needing the workaround, with
+	 * 4 and 1 iterations respectively.
+	 */
 
-	val = hdmi_readb(hdmi, HDMI_FC_INVIDCONF);
-	if (hdmi->dev_type == IMX6DL_HDMI) {
-		hdmi_writeb(hdmi, val, HDMI_FC_INVIDCONF);
+	switch (hdmi->version) {
+	case 0x130a:
+		count = 4;
+		break;
+	case 0x131a:
+		count = 1;
+		break;
+	default:
 		return;
 	}
 
-	for (count = 0; count < 4; count++)
+	/* TMDS software reset */
+	hdmi_writeb(hdmi, (u8)~HDMI_MC_SWRSTZ_TMDSSWRST_REQ, HDMI_MC_SWRSTZ);
+
+	val = hdmi_readb(hdmi, HDMI_FC_INVIDCONF);
+	for (i = 0; i < count; i++)
 		hdmi_writeb(hdmi, val, HDMI_FC_INVIDCONF);
 }
 
@@ -1832,7 +1853,6 @@ __dw_hdmi_probe(struct platform_device *pdev,
 	int irq;
 	int ret;
 	u32 val = 1;
-	u16 version;
 	u8 prod_id0;
 	u8 prod_id1;
 	u8 config0;
@@ -1917,7 +1937,7 @@ __dw_hdmi_probe(struct platform_device *pdev,
 	}
 
 	/* Product and revision IDs */
-	version = (hdmi_readb(hdmi, HDMI_DESIGN_ID) << 8)
+	hdmi->version = (hdmi_readb(hdmi, HDMI_DESIGN_ID) << 8)
 		      | (hdmi_readb(hdmi, HDMI_REVISION_ID) << 0);
 	prod_id0 = hdmi_readb(hdmi, HDMI_PRODUCT_ID0);
 	prod_id1 = hdmi_readb(hdmi, HDMI_PRODUCT_ID1);
@@ -1925,13 +1945,13 @@ __dw_hdmi_probe(struct platform_device *pdev,
 	if (prod_id0 != HDMI_PRODUCT_ID0_HDMI_TX ||
 	    (prod_id1 & ~HDMI_PRODUCT_ID1_HDCP) != HDMI_PRODUCT_ID1_HDMI_TX) {
 		dev_err(dev, "Unsupported HDMI controller (%04x:%02x:%02x)\n",
-			version, prod_id0, prod_id1);
+			hdmi->version, prod_id0, prod_id1);
 		ret = -ENODEV;
 		goto err_iahb;
 	}
 
 	dev_info(dev, "Detected HDMI TX controller v%x.%03x %s HDCP\n",
-		 version >> 12, version & 0xfff,
+		 hdmi->version >> 12, hdmi->version & 0xfff,
 		 prod_id1 & HDMI_PRODUCT_ID1_HDCP ? "with" : "without");
 
 	initialize_hdmi_ih_mutes(hdmi);