drm: bridge/dw_hdmi: add support for multi-byte register width access

On rockchip rk3288, only word(32-bit) accesses are
permitted for hdmi registers.  Byte width accesses (writeb,
readb) generate an imprecise external abort.
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

@@ -128,18 +128,41 @@ struct dw_hdmi {
 
 	unsigned int sample_rate;
 	int ratio;
+
+	void (*write)(struct dw_hdmi *hdmi, u8 val, int offset);
+	u8 (*read)(struct dw_hdmi *hdmi, int offset);
 };
 
-static inline void hdmi_writeb(struct dw_hdmi *hdmi, u8 val, int offset)
+static void dw_hdmi_writel(struct dw_hdmi *hdmi, u8 val, int offset)
+{
+	writel(val, hdmi->regs + (offset << 2));
+}
+
+static u8 dw_hdmi_readl(struct dw_hdmi *hdmi, int offset)
+{
+	return readl(hdmi->regs + (offset << 2));
+}
+
+static void dw_hdmi_writeb(struct dw_hdmi *hdmi, u8 val, int offset)
 {
 	writeb(val, hdmi->regs + offset);
 }
 
-static inline u8 hdmi_readb(struct dw_hdmi *hdmi, int offset)
+static u8 dw_hdmi_readb(struct dw_hdmi *hdmi, int offset)
 {
 	return readb(hdmi->regs + offset);
 }
 
+static inline void hdmi_writeb(struct dw_hdmi *hdmi, u8 val, int offset)
+{
+	hdmi->write(hdmi, val, offset);
+}
+
+static inline u8 hdmi_readb(struct dw_hdmi *hdmi, int offset)
+{
+	return hdmi->read(hdmi, offset);
+}
+
 static void hdmi_modb(struct dw_hdmi *hdmi, u8 data, u8 mask, unsigned reg)
 {
 	u8 val = hdmi_readb(hdmi, reg) & ~mask;
@@ -1511,6 +1534,7 @@ int dw_hdmi_bind(struct device *dev, struct device *master,
 	struct device_node *ddc_node;
 	struct dw_hdmi *hdmi;
 	int ret;
+	u32 val = 1;
 
 	hdmi = devm_kzalloc(dev, sizeof(*hdmi), GFP_KERNEL);
 	if (!hdmi)
@@ -1523,6 +1547,22 @@ int dw_hdmi_bind(struct device *dev, struct device *master,
 	hdmi->ratio = 100;
 	hdmi->encoder = encoder;
 
+	of_property_read_u32(np, "reg-io-width", &val);
+
+	switch (val) {
+	case 4:
+		hdmi->write = dw_hdmi_writel;
+		hdmi->read = dw_hdmi_readl;
+		break;
+	case 1:
+		hdmi->write = dw_hdmi_writeb;
+		hdmi->read = dw_hdmi_readb;
+		break;
+	default:
+		dev_err(dev, "reg-io-width must be 1 or 4\n");
+		return -EINVAL;
+	}
+
 	ddc_node = of_parse_phandle(np, "ddc-i2c-bus", 0);
 	if (ddc_node) {
 		hdmi->ddc = of_find_i2c_adapter_by_node(ddc_node);