Implement a way to determine when the panel is connected. This is done
by reading REG_ID through I2C. We consider the panel as disconnect
until we retrieve a valid ID.

Signed-off-by: Boris Brezillon <boris.brezil...@bootlin.com>
---
 .../gpu/drm/panel/panel-raspberrypi-touchscreen.c  | 62 ++++++++++++++++++----
 1 file changed, 53 insertions(+), 9 deletions(-)

diff --git a/drivers/gpu/drm/panel/panel-raspberrypi-touchscreen.c 
b/drivers/gpu/drm/panel/panel-raspberrypi-touchscreen.c
index d964d454e4ae..e65caec590d4 100644
--- a/drivers/gpu/drm/panel/panel-raspberrypi-touchscreen.c
+++ b/drivers/gpu/drm/panel/panel-raspberrypi-touchscreen.c
@@ -196,6 +196,7 @@ struct rpi_touchscreen {
        struct drm_panel base;
        struct mipi_dsi_device *dsi;
        struct i2c_client *i2c;
+       bool connected;
 };
 
 static const struct drm_display_mode rpi_touchscreen_modes[] = {
@@ -255,6 +256,9 @@ static int rpi_touchscreen_write(struct rpi_touchscreen 
*ts, u16 reg, u32 val)
 
        mipi_dsi_dcs_write_buffer(ts->dsi, msg, sizeof(msg));
 #else
+       if (!ts->connected)
+               return 0;
+
        rpi_touchscreen_i2c_write(ts, REG_WR_ADDRH, reg >> 8);
        rpi_touchscreen_i2c_write(ts, REG_WR_ADDRL, reg);
        rpi_touchscreen_i2c_write(ts, REG_WRITEH, val >> 8);
@@ -268,6 +272,9 @@ static int rpi_touchscreen_disable(struct drm_panel *panel)
 {
        struct rpi_touchscreen *ts = panel_to_ts(panel);
 
+       if (!ts->connected)
+               return 0;
+
        rpi_touchscreen_i2c_write(ts, REG_PWM, 0);
 
        rpi_touchscreen_i2c_write(ts, REG_POWERON, 0);
@@ -286,6 +293,9 @@ static int rpi_touchscreen_enable(struct drm_panel *panel)
        struct rpi_touchscreen *ts = panel_to_ts(panel);
        int i;
 
+       if (!ts->connected)
+               return 0;
+
        rpi_touchscreen_i2c_write(ts, REG_POWERON, 1);
        /* Wait for nPWRDWN to go low to indicate poweron is done. */
        for (i = 0; i < 100; i++) {
@@ -330,6 +340,10 @@ static int rpi_touchscreen_get_modes(struct drm_panel 
*panel)
        struct drm_device *drm = panel->drm;
        unsigned int i, num = 0;
        static const u32 bus_format = MEDIA_BUS_FMT_RGB888_1X24;
+       struct rpi_touchscreen *ts = panel_to_ts(panel);
+
+       if (!ts->connected)
+               return 0;
 
        for (i = 0; i < ARRAY_SIZE(rpi_touchscreen_modes); i++) {
                const struct drm_display_mode *m = &rpi_touchscreen_modes[i];
@@ -362,7 +376,34 @@ static int rpi_touchscreen_get_modes(struct drm_panel 
*panel)
        return num;
 }
 
+static int rpi_touchscreen_detect(struct drm_panel *panel)
+{
+       struct rpi_touchscreen *ts = panel_to_ts(panel);
+       int ver;
+
+       if (ts->connected)
+               return connector_status_connected;
+
+       ver = rpi_touchscreen_i2c_read(ts, REG_ID);
+       switch (ver) {
+       case 0xde: /* ver 1 */
+       case 0xc3: /* ver 2 */
+               ts->connected = true;
+
+               /* Turn off at boot, so we can cleanly sequence powering on. */
+               rpi_touchscreen_i2c_write(ts, REG_POWERON, 0);
+
+               return connector_status_connected;
+
+       default:
+               break;
+       }
+
+       return connector_status_disconnected;
+}
+
 static const struct drm_panel_funcs rpi_touchscreen_funcs = {
+       .detect = rpi_touchscreen_detect,
        .disable = rpi_touchscreen_disable,
        .unprepare = rpi_touchscreen_noop,
        .prepare = rpi_touchscreen_noop,
@@ -393,22 +434,24 @@ static int rpi_touchscreen_probe(struct i2c_client *i2c,
        ts->i2c = i2c;
 
        ver = rpi_touchscreen_i2c_read(ts, REG_ID);
-       if (ver < 0) {
-               dev_err(dev, "Atmel I2C read failed: %d\n", ver);
-               return -ENODEV;
-       }
-
        switch (ver) {
        case 0xde: /* ver 1 */
        case 0xc3: /* ver 2 */
+               ts->connected = true;
+
+               /* Turn off at boot, so we can cleanly sequence powering on. */
+               rpi_touchscreen_i2c_write(ts, REG_POWERON, 0);
                break;
        default:
-               dev_err(dev, "Unknown Atmel firmware revision: 0x%02x\n", ver);
-               return -ENODEV;
+               if (ver < 0)
+                       dev_err(dev, "Atmel I2C read failed: %d\n", ver);
+               else
+                       dev_err(dev,
+                               "Unknown Atmel firmware revision: 0x%02x\n",
+                               ver);
+               break;
        }
 
-       /* Turn off at boot, so we can cleanly sequence powering on. */
-       rpi_touchscreen_i2c_write(ts, REG_POWERON, 0);
 
        /* Look up the DSI host.  It needs to probe before we do. */
        endpoint = of_graph_get_next_endpoint(dev->of_node, NULL);
@@ -432,6 +475,7 @@ static int rpi_touchscreen_probe(struct i2c_client *i2c,
 
        ts->base.dev = dev;
        ts->base.funcs = &rpi_touchscreen_funcs;
+       ts->base.polled = DRM_CONNECTOR_POLL_CONNECT;
 
        /* This appears last, as it's what will unblock the DSI host
         * driver's component bind function.
-- 
2.14.1

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