drm/panel/raspberrypi-touchscreen: Use independent I2C actions with delay.

We now have the hardware I2C controller pinmuxed to the drive the
display I2C, but this controller does not support clock stretching.
The Atmel micro-controller in the panel requires clock stretching
to allow it to prepare any data to be read.

Split the rpi_touchscreen_i2c_read into two independent transactions with
a delay between them for the Atmel to prepare the data.

Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>

diff --git a/drivers/gpu/drm/panel/panel-raspberrypi-touchscreen.c b/drivers/gpu/drm/panel/panel-raspberrypi-touchscreen.c
index 5e9ccef..7ebb5ee 100644 (file)
--- a/drivers/gpu/drm/panel/panel-raspberrypi-touchscreen.c
+++ b/drivers/gpu/drm/panel/panel-raspberrypi-touchscreen.c
@@ -219,7 +219,35 @@ static struct rpi_touchscreen *panel_to_ts(struct drm_panel *panel)
 
 static int rpi_touchscreen_i2c_read(struct rpi_touchscreen *ts, u8 reg)
 {
-       return i2c_smbus_read_byte_data(ts->i2c, reg);
+       struct i2c_client *client = ts->i2c;
+       struct i2c_msg msgs[1];
+       u8 addr_buf[1] = { reg };
+       u8 data_buf[1] = { 0, };
+       int ret;
+
+       /* Write register address */
+       msgs[0].addr = client->addr;
+       msgs[0].flags = 0;
+       msgs[0].len = ARRAY_SIZE(addr_buf);
+       msgs[0].buf = addr_buf;
+
+       ret = i2c_transfer(client->adapter, msgs, ARRAY_SIZE(msgs));
+       if (ret != ARRAY_SIZE(msgs))
+               return -EIO;
+
+       usleep_range(100, 300);
+
+       /* Read data from register */
+       msgs[0].addr = client->addr;
+       msgs[0].flags = I2C_M_RD;
+       msgs[0].len = 1;
+       msgs[0].buf = data_buf;
+
+       ret = i2c_transfer(client->adapter, msgs, ARRAY_SIZE(msgs));
+       if (ret != ARRAY_SIZE(msgs))
+               return -EIO;
+
+       return data_buf[0];
 }
 
 static void rpi_touchscreen_i2c_write(struct rpi_touchscreen *ts,