drm/sun4i: hdmi: Implement I2C adapter for A10s DDC bus

The documentation for drm_do_get_edid in drivers/gpu/drm/drm_edid.c states:
"As in the general case the DDC bus is accessible by the kernel at the I2C
level, drivers must make all reasonable efforts to expose it as an I2C
adapter and use drm_get_edid() instead of abusing this function."

Exposing the DDC bus as an I2C adapter is more beneficial as it can be used
for purposes other than reading the EDID such as modifying the EDID or
using the HDMI DDC pins as an I2C bus through the I2C dev interface from
userspace (e.g. i2c-tools).

Implement this for A10s.
Signed-off-by: Jonathan Liu <net147@gmail.com>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>

drivers/gpu/drm/sun4i/Makefile

@@ -2,6 +2,7 @@ sun4i-drm-y += sun4i_drv.o
 sun4i-drm-y += sun4i_framebuffer.o
 
 sun4i-drm-hdmi-y += sun4i_hdmi_enc.o
+sun4i-drm-hdmi-y += sun4i_hdmi_i2c.o
 sun4i-drm-hdmi-y += sun4i_hdmi_ddc_clk.o
 sun4i-drm-hdmi-y += sun4i_hdmi_tmds_clk.o
 

drivers/gpu/drm/sun4i/sun4i_hdmi.h

@@ -96,6 +96,7 @@
 #define SUN4I_HDMI_DDC_CTRL_ENABLE		BIT(31)
 #define SUN4I_HDMI_DDC_CTRL_START_CMD		BIT(30)
 #define SUN4I_HDMI_DDC_CTRL_FIFO_DIR_MASK	BIT(8)
+#define SUN4I_HDMI_DDC_CTRL_FIFO_DIR_WRITE	(1 << 8)
 #define SUN4I_HDMI_DDC_CTRL_FIFO_DIR_READ	(0 << 8)
 #define SUN4I_HDMI_DDC_CTRL_RESET		BIT(0)
 
@@ -105,14 +106,34 @@
 #define SUN4I_HDMI_DDC_ADDR_OFFSET(off)		(((off) & 0xff) << 8)
 #define SUN4I_HDMI_DDC_ADDR_SLAVE(addr)		((addr) & 0xff)
 
+#define SUN4I_HDMI_DDC_INT_STATUS_REG		0x50c
+#define SUN4I_HDMI_DDC_INT_STATUS_ILLEGAL_FIFO_OPERATION	BIT(7)
+#define SUN4I_HDMI_DDC_INT_STATUS_DDC_RX_FIFO_UNDERFLOW		BIT(6)
+#define SUN4I_HDMI_DDC_INT_STATUS_DDC_TX_FIFO_OVERFLOW		BIT(5)
+#define SUN4I_HDMI_DDC_INT_STATUS_FIFO_REQUEST			BIT(4)
+#define SUN4I_HDMI_DDC_INT_STATUS_ARBITRATION_ERROR		BIT(3)
+#define SUN4I_HDMI_DDC_INT_STATUS_ACK_ERROR			BIT(2)
+#define SUN4I_HDMI_DDC_INT_STATUS_BUS_ERROR			BIT(1)
+#define SUN4I_HDMI_DDC_INT_STATUS_TRANSFER_COMPLETE		BIT(0)
+
 #define SUN4I_HDMI_DDC_FIFO_CTRL_REG	0x510
 #define SUN4I_HDMI_DDC_FIFO_CTRL_CLEAR		BIT(31)
+#define SUN4I_HDMI_DDC_FIFO_CTRL_RX_THRES(n)	(((n) & 0xf) << 4)
+#define SUN4I_HDMI_DDC_FIFO_CTRL_RX_THRES_MASK	GENMASK(7, 4)
+#define SUN4I_HDMI_DDC_FIFO_CTRL_RX_THRES_MAX	(BIT(4) - 1)
+#define SUN4I_HDMI_DDC_FIFO_CTRL_TX_THRES(n)	((n) & 0xf)
+#define SUN4I_HDMI_DDC_FIFO_CTRL_TX_THRES_MASK	GENMASK(3, 0)
+#define SUN4I_HDMI_DDC_FIFO_CTRL_TX_THRES_MAX	(BIT(4) - 1)
 
 #define SUN4I_HDMI_DDC_FIFO_DATA_REG	0x518
+
 #define SUN4I_HDMI_DDC_BYTE_COUNT_REG	0x51c
+#define SUN4I_HDMI_DDC_BYTE_COUNT_MAX		(BIT(10) - 1)
 
 #define SUN4I_HDMI_DDC_CMD_REG		0x520
 #define SUN4I_HDMI_DDC_CMD_EXPLICIT_EDDC_READ	6
+#define SUN4I_HDMI_DDC_CMD_IMPLICIT_READ	5
+#define SUN4I_HDMI_DDC_CMD_IMPLICIT_WRITE	3
 
 #define SUN4I_HDMI_DDC_CLK_REG		0x528
 #define SUN4I_HDMI_DDC_CLK_M(m)			(((m) & 0x7) << 3)
@@ -146,6 +167,8 @@ struct sun4i_hdmi {
 	struct clk		*ddc_clk;
 	struct clk		*tmds_clk;
 
+	struct i2c_adapter	*i2c;
+
 	struct sun4i_drv	*drv;
 
 	bool			hdmi_monitor;
@@ -153,5 +176,6 @@ struct sun4i_hdmi {
 
 int sun4i_ddc_create(struct sun4i_hdmi *hdmi, struct clk *clk);
 int sun4i_tmds_create(struct sun4i_hdmi *hdmi);
+int sun4i_hdmi_i2c_create(struct device *dev, struct sun4i_hdmi *hdmi);
 
 #endif /* _SUN4I_HDMI_H_ */

drivers/gpu/drm/sun4i/sun4i_hdmi_enc.c

@@ -29,8 +29,6 @@
 #include "sun4i_hdmi.h"
 #include "sun4i_tcon.h"
 
-#define DDC_SEGMENT_ADDR	0x30
-
 static inline struct sun4i_hdmi *
 drm_encoder_to_sun4i_hdmi(struct drm_encoder *encoder)
 {
@@ -184,93 +182,13 @@ static const struct drm_encoder_funcs sun4i_hdmi_funcs = {
 	.destroy	= drm_encoder_cleanup,
 };
 
-static int sun4i_hdmi_read_sub_block(struct sun4i_hdmi *hdmi,
-				     unsigned int blk, unsigned int offset,
-				     u8 *buf, unsigned int count)
-{
-	unsigned long reg;
-	int i;
-
-	reg = readl(hdmi->base + SUN4I_HDMI_DDC_CTRL_REG);
-	reg &= ~SUN4I_HDMI_DDC_CTRL_FIFO_DIR_MASK;
-	writel(reg | SUN4I_HDMI_DDC_CTRL_FIFO_DIR_READ,
-	       hdmi->base + SUN4I_HDMI_DDC_CTRL_REG);
-
-	writel(SUN4I_HDMI_DDC_ADDR_SEGMENT(offset >> 8) |
-	       SUN4I_HDMI_DDC_ADDR_EDDC(DDC_SEGMENT_ADDR << 1) |
-	       SUN4I_HDMI_DDC_ADDR_OFFSET(offset) |
-	       SUN4I_HDMI_DDC_ADDR_SLAVE(DDC_ADDR),
-	       hdmi->base + SUN4I_HDMI_DDC_ADDR_REG);
-
-	reg = readl(hdmi->base + SUN4I_HDMI_DDC_FIFO_CTRL_REG);
-	writel(reg | SUN4I_HDMI_DDC_FIFO_CTRL_CLEAR,
-	       hdmi->base + SUN4I_HDMI_DDC_FIFO_CTRL_REG);
-
-	writel(count, hdmi->base + SUN4I_HDMI_DDC_BYTE_COUNT_REG);
-	writel(SUN4I_HDMI_DDC_CMD_EXPLICIT_EDDC_READ,
-	       hdmi->base + SUN4I_HDMI_DDC_CMD_REG);
-
-	reg = readl(hdmi->base + SUN4I_HDMI_DDC_CTRL_REG);
-	writel(reg | SUN4I_HDMI_DDC_CTRL_START_CMD,
-	       hdmi->base + SUN4I_HDMI_DDC_CTRL_REG);
-
-	if (readl_poll_timeout(hdmi->base + SUN4I_HDMI_DDC_CTRL_REG, reg,
-			       !(reg & SUN4I_HDMI_DDC_CTRL_START_CMD),
-			       100, 100000))
-		return -EIO;
-
-	for (i = 0; i < count; i++)
-		buf[i] = readb(hdmi->base + SUN4I_HDMI_DDC_FIFO_DATA_REG);
-
-	return 0;
-}
-
-static int sun4i_hdmi_read_edid_block(void *data, u8 *buf, unsigned int blk,
-				      size_t length)
-{
-	struct sun4i_hdmi *hdmi = data;
-	int retry = 2, i;
-
-	do {
-		for (i = 0; i < length; i += SUN4I_HDMI_DDC_FIFO_SIZE) {
-			unsigned char offset = blk * EDID_LENGTH + i;
-			unsigned int count = min((unsigned int)SUN4I_HDMI_DDC_FIFO_SIZE,
-						 length - i);
-			int ret;
-
-			ret = sun4i_hdmi_read_sub_block(hdmi, blk, offset,
-							buf + i, count);
-			if (ret)
-				return ret;
-		}
-	} while (!drm_edid_block_valid(buf, blk, true, NULL) && (retry--));
-
-	return 0;
-}
-
 static int sun4i_hdmi_get_modes(struct drm_connector *connector)
 {
 	struct sun4i_hdmi *hdmi = drm_connector_to_sun4i_hdmi(connector);
-	unsigned long reg;
 	struct edid *edid;
 	int ret;
 
-	/* Reset i2c controller */
-	writel(SUN4I_HDMI_DDC_CTRL_ENABLE | SUN4I_HDMI_DDC_CTRL_RESET,
-	       hdmi->base + SUN4I_HDMI_DDC_CTRL_REG);
-	if (readl_poll_timeout(hdmi->base + SUN4I_HDMI_DDC_CTRL_REG, reg,
-			       !(reg & SUN4I_HDMI_DDC_CTRL_RESET),
-			       100, 2000))
-		return -EIO;
-
-	writel(SUN4I_HDMI_DDC_LINE_CTRL_SDA_ENABLE |
-	       SUN4I_HDMI_DDC_LINE_CTRL_SCL_ENABLE,
-	       hdmi->base + SUN4I_HDMI_DDC_LINE_CTRL_REG);
-
-	clk_prepare_enable(hdmi->ddc_clk);
-	clk_set_rate(hdmi->ddc_clk, 100000);
-
-	edid = drm_do_get_edid(connector, sun4i_hdmi_read_edid_block, hdmi);
+	edid = drm_get_edid(connector, hdmi->i2c);
 	if (!edid)
 		return 0;
 
@@ -282,8 +200,6 @@ static int sun4i_hdmi_get_modes(struct drm_connector *connector)
 	ret = drm_add_edid_modes(connector, edid);
 	kfree(edid);
 
-	clk_disable_unprepare(hdmi->ddc_clk);
-
 	return ret;
 }
 
@@ -407,9 +323,9 @@ static int sun4i_hdmi_bind(struct device *dev, struct device *master,
 		SUN4I_HDMI_PLL_CTRL_PLL_EN;
 	writel(reg, hdmi->base + SUN4I_HDMI_PLL_CTRL_REG);
 
-	ret = sun4i_ddc_create(hdmi, hdmi->tmds_clk);
+	ret = sun4i_hdmi_i2c_create(dev, hdmi);
 	if (ret) {
-		dev_err(dev, "Couldn't create the DDC clock\n");
+		dev_err(dev, "Couldn't create the HDMI I2C adapter\n");
 		return ret;
 	}
 
@@ -422,13 +338,15 @@ static int sun4i_hdmi_bind(struct device *dev, struct device *master,
 			       NULL);
 	if (ret) {
 		dev_err(dev, "Couldn't initialise the HDMI encoder\n");
-		return ret;
+		goto err_del_i2c_adapter;
 	}
 
 	hdmi->encoder.possible_crtcs = drm_of_find_possible_crtcs(drm,
 								  dev->of_node);
-	if (!hdmi->encoder.possible_crtcs)
-		return -EPROBE_DEFER;
+	if (!hdmi->encoder.possible_crtcs) {
+		ret = -EPROBE_DEFER;
+		goto err_del_i2c_adapter;
+	}
 
 	drm_connector_helper_add(&hdmi->connector,
 				 &sun4i_hdmi_connector_helper_funcs);
@@ -451,6 +369,8 @@ static int sun4i_hdmi_bind(struct device *dev, struct device *master,
 
 err_cleanup_connector:
 	drm_encoder_cleanup(&hdmi->encoder);
+err_del_i2c_adapter:
+	i2c_del_adapter(hdmi->i2c);
 	return ret;
 }
 
@@ -461,6 +381,7 @@ static void sun4i_hdmi_unbind(struct device *dev, struct device *master,
 
 	drm_connector_cleanup(&hdmi->connector);
 	drm_encoder_cleanup(&hdmi->encoder);
+	i2c_del_adapter(hdmi->i2c);
 }
 
 static const struct component_ops sun4i_hdmi_ops = {

drivers/gpu/drm/sun4i/sun4i_hdmi_i2c.c

+/*
+ * Copyright (C) 2016 Maxime Ripard <maxime.ripard@free-electrons.com>
+ * Copyright (C) 2017 Jonathan Liu <net147@gmail.com>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of
+ * the License, or (at your option) any later version.
+ */
+
+#include <linux/clk.h>
+#include <linux/i2c.h>
+#include <linux/iopoll.h>
+
+#include "sun4i_hdmi.h"
+
+#define SUN4I_HDMI_DDC_INT_STATUS_ERROR_MASK ( \
+	SUN4I_HDMI_DDC_INT_STATUS_ILLEGAL_FIFO_OPERATION | \
+	SUN4I_HDMI_DDC_INT_STATUS_DDC_RX_FIFO_UNDERFLOW | \
+	SUN4I_HDMI_DDC_INT_STATUS_DDC_TX_FIFO_OVERFLOW | \
+	SUN4I_HDMI_DDC_INT_STATUS_ARBITRATION_ERROR | \
+	SUN4I_HDMI_DDC_INT_STATUS_ACK_ERROR | \
+	SUN4I_HDMI_DDC_INT_STATUS_BUS_ERROR \
+)
+
+/* FIFO request bit is set when FIFO level is above RX_THRESHOLD during read */
+#define RX_THRESHOLD SUN4I_HDMI_DDC_FIFO_CTRL_RX_THRES_MAX
+/* FIFO request bit is set when FIFO level is below TX_THRESHOLD during write */
+#define TX_THRESHOLD 1
+
+static int fifo_transfer(struct sun4i_hdmi *hdmi, u8 *buf, int len, bool read)
+{
+	/*
+	 * 1 byte takes 9 clock cycles (8 bits + 1 ACK) = 90 us for 100 kHz
+	 * clock. As clock rate is fixed, just round it up to 100 us.
+	 */
+	const unsigned long byte_time_ns = 100;
+	const u32 mask = SUN4I_HDMI_DDC_INT_STATUS_ERROR_MASK |
+			 SUN4I_HDMI_DDC_INT_STATUS_FIFO_REQUEST |
+			 SUN4I_HDMI_DDC_INT_STATUS_TRANSFER_COMPLETE;
+	u32 reg;
+
+	/* Limit transfer length by FIFO threshold */
+	len = min_t(int, len, read ? (RX_THRESHOLD + 1) :
+			      (SUN4I_HDMI_DDC_FIFO_SIZE - TX_THRESHOLD + 1));
+
+	/* Wait until error, FIFO request bit set or transfer complete */
+	if (readl_poll_timeout(hdmi->base + SUN4I_HDMI_DDC_INT_STATUS_REG, reg,
+			       reg & mask, len * byte_time_ns, 100000))
+		return -ETIMEDOUT;
+
+	if (reg & SUN4I_HDMI_DDC_INT_STATUS_ERROR_MASK)
+		return -EIO;
+
+	if (read)
+		readsb(hdmi->base + SUN4I_HDMI_DDC_FIFO_DATA_REG, buf, len);
+	else
+		writesb(hdmi->base + SUN4I_HDMI_DDC_FIFO_DATA_REG, buf, len);
+
+	/* Clear FIFO request bit */
+	writel(SUN4I_HDMI_DDC_INT_STATUS_FIFO_REQUEST,
+	       hdmi->base + SUN4I_HDMI_DDC_INT_STATUS_REG);
+
+	return len;
+}
+
+static int xfer_msg(struct sun4i_hdmi *hdmi, struct i2c_msg *msg)
+{
+	int i, len;
+	u32 reg;
+
+	/* Set FIFO direction */
+	reg = readl(hdmi->base + SUN4I_HDMI_DDC_CTRL_REG);
+	reg &= ~SUN4I_HDMI_DDC_CTRL_FIFO_DIR_MASK;
+	reg |= (msg->flags & I2C_M_RD) ?
+	       SUN4I_HDMI_DDC_CTRL_FIFO_DIR_READ :
+	       SUN4I_HDMI_DDC_CTRL_FIFO_DIR_WRITE;
+	writel(reg, hdmi->base + SUN4I_HDMI_DDC_CTRL_REG);
+
+	/* Set I2C address */
+	writel(SUN4I_HDMI_DDC_ADDR_SLAVE(msg->addr),
+	       hdmi->base + SUN4I_HDMI_DDC_ADDR_REG);
+
+	/* Set FIFO RX/TX thresholds and clear FIFO */
+	reg = readl(hdmi->base + SUN4I_HDMI_DDC_FIFO_CTRL_REG);
+	reg |= SUN4I_HDMI_DDC_FIFO_CTRL_CLEAR;
+	reg &= ~SUN4I_HDMI_DDC_FIFO_CTRL_RX_THRES_MASK;
+	reg |= SUN4I_HDMI_DDC_FIFO_CTRL_RX_THRES(RX_THRESHOLD);
+	reg &= ~SUN4I_HDMI_DDC_FIFO_CTRL_TX_THRES_MASK;
+	reg |= SUN4I_HDMI_DDC_FIFO_CTRL_TX_THRES(TX_THRESHOLD);
+	writel(reg, hdmi->base + SUN4I_HDMI_DDC_FIFO_CTRL_REG);
+	if (readl_poll_timeout(hdmi->base + SUN4I_HDMI_DDC_FIFO_CTRL_REG,
+			       reg,
+			       !(reg & SUN4I_HDMI_DDC_FIFO_CTRL_CLEAR),
+			       100, 2000))
+		return -EIO;
+
+	/* Set transfer length */
+	writel(msg->len, hdmi->base + SUN4I_HDMI_DDC_BYTE_COUNT_REG);
+
+	/* Set command */
+	writel(msg->flags & I2C_M_RD ?
+	       SUN4I_HDMI_DDC_CMD_IMPLICIT_READ :
+	       SUN4I_HDMI_DDC_CMD_IMPLICIT_WRITE,
+	       hdmi->base + SUN4I_HDMI_DDC_CMD_REG);
+
+	/* Clear interrupt status bits */
+	writel(SUN4I_HDMI_DDC_INT_STATUS_ERROR_MASK |
+	       SUN4I_HDMI_DDC_INT_STATUS_FIFO_REQUEST |
+	       SUN4I_HDMI_DDC_INT_STATUS_TRANSFER_COMPLETE,
+	       hdmi->base + SUN4I_HDMI_DDC_INT_STATUS_REG);
+
+	/* Start command */
+	reg = readl(hdmi->base + SUN4I_HDMI_DDC_CTRL_REG);
+	writel(reg | SUN4I_HDMI_DDC_CTRL_START_CMD,
+	       hdmi->base + SUN4I_HDMI_DDC_CTRL_REG);
+
+	/* Transfer bytes */
+	for (i = 0; i < msg->len; i += len) {
+		len = fifo_transfer(hdmi, msg->buf + i, msg->len - i,
+				    msg->flags & I2C_M_RD);
+		if (len <= 0)
+			return len;
+	}
+
+	/* Wait for command to finish */
+	if (readl_poll_timeout(hdmi->base + SUN4I_HDMI_DDC_CTRL_REG,
+			       reg,
+			       !(reg & SUN4I_HDMI_DDC_CTRL_START_CMD),
+			       100, 100000))
+		return -EIO;
+
+	/* Check for errors */
+	reg = readl(hdmi->base + SUN4I_HDMI_DDC_INT_STATUS_REG);
+	if ((reg & SUN4I_HDMI_DDC_INT_STATUS_ERROR_MASK) ||
+	    !(reg & SUN4I_HDMI_DDC_INT_STATUS_TRANSFER_COMPLETE)) {
+		return -EIO;
+	}
+
+	return 0;
+}
+
+static int sun4i_hdmi_i2c_xfer(struct i2c_adapter *adap,
+			       struct i2c_msg *msgs, int num)
+{
+	struct sun4i_hdmi *hdmi = i2c_get_adapdata(adap);
+	u32 reg;
+	int err, i, ret = num;
+
+	for (i = 0; i < num; i++) {
+		if (!msgs[i].len)
+			return -EINVAL;
+		if (msgs[i].len > SUN4I_HDMI_DDC_BYTE_COUNT_MAX)
+			return -EINVAL;
+	}
+
+	/* Reset I2C controller */
+	writel(SUN4I_HDMI_DDC_CTRL_ENABLE | SUN4I_HDMI_DDC_CTRL_RESET,
+	       hdmi->base + SUN4I_HDMI_DDC_CTRL_REG);
+	if (readl_poll_timeout(hdmi->base + SUN4I_HDMI_DDC_CTRL_REG, reg,
+			       !(reg & SUN4I_HDMI_DDC_CTRL_RESET),
+			       100, 2000))
+		return -EIO;
+
+	writel(SUN4I_HDMI_DDC_LINE_CTRL_SDA_ENABLE |
+	       SUN4I_HDMI_DDC_LINE_CTRL_SCL_ENABLE,
+	       hdmi->base + SUN4I_HDMI_DDC_LINE_CTRL_REG);
+
+	clk_prepare_enable(hdmi->ddc_clk);
+	clk_set_rate(hdmi->ddc_clk, 100000);
+
+	for (i = 0; i < num; i++) {
+		err = xfer_msg(hdmi, &msgs[i]);
+		if (err) {
+			ret = err;
+			break;
+		}
+	}
+
+	clk_disable_unprepare(hdmi->ddc_clk);
+	return ret;
+}
+
+static u32 sun4i_hdmi_i2c_func(struct i2c_adapter *adap)
+{
+	return I2C_FUNC_I2C | I2C_FUNC_SMBUS_EMUL;
+}
+
+static const struct i2c_algorithm sun4i_hdmi_i2c_algorithm = {
+	.master_xfer	= sun4i_hdmi_i2c_xfer,
+	.functionality	= sun4i_hdmi_i2c_func,
+};
+
+int sun4i_hdmi_i2c_create(struct device *dev, struct sun4i_hdmi *hdmi)
+{
+	struct i2c_adapter *adap;
+	int ret = 0;
+
+	ret = sun4i_ddc_create(hdmi, hdmi->tmds_clk);
+	if (ret)
+		return ret;
+
+	adap = devm_kzalloc(dev, sizeof(*adap), GFP_KERNEL);
+	if (!adap)
+		return -ENOMEM;
+
+	adap->owner = THIS_MODULE;
+	adap->class = I2C_CLASS_DDC;
+	adap->algo = &sun4i_hdmi_i2c_algorithm;
+	strlcpy(adap->name, "sun4i_hdmi_i2c adapter", sizeof(adap->name));
+	i2c_set_adapdata(adap, hdmi);
+
+	ret = i2c_add_adapter(adap);
+	if (ret)
+		return ret;
+
+	hdmi->i2c = adap;
+
+	return ret;
+}