drm/tilcdc fixing i2c/slave initialization race

In certain senarios drm will initialize before i2c this means that i2c
slave devices like the nxp tda998x will fail to be probed.  This patch
detects this condition then defers the probe of the slave device and
the tilcdc main driver.

Signed-off-by: Darren Etheridge <detheridge@ti.com>
Acked-by: Rob Clark <robdclark@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/tilcdc/tilcdc_drv.c

@@ -26,6 +26,7 @@
 #include "drm_fb_helper.h"
 
 static LIST_HEAD(module_list);
+static bool slave_probing;
 
 void tilcdc_module_init(struct tilcdc_module *mod, const char *name,
 		const struct tilcdc_module_ops *funcs)
@@ -41,6 +42,11 @@ void tilcdc_module_cleanup(struct tilcdc_module *mod)
 	list_del(&mod->list);
 }
 
+void tilcdc_slave_probedefer(bool defered)
+{
+	slave_probing = defered;
+}
+
 static struct of_device_id tilcdc_of_match[];
 
 static struct drm_framebuffer *tilcdc_fb_create(struct drm_device *dev,
@@ -580,6 +586,10 @@ static int tilcdc_pdev_probe(struct platform_device *pdev)
 		return -ENXIO;
 	}
 
+	/* defer probing if slave is in deferred probing */
+	if (slave_probing == true)
+		return -EPROBE_DEFER;
+
 	return drm_platform_init(&tilcdc_driver, pdev);
 }
 

drivers/gpu/drm/tilcdc/tilcdc_drv.h

@@ -117,7 +117,7 @@ struct tilcdc_module {
 void tilcdc_module_init(struct tilcdc_module *mod, const char *name,
 		const struct tilcdc_module_ops *funcs);
 void tilcdc_module_cleanup(struct tilcdc_module *mod);
-
+void tilcdc_slave_probedefer(bool defered);
 
 /* Panel config that needs to be set in the crtc, but is not coming from
  * the mode timings.  The display module is expected to call

drivers/gpu/drm/tilcdc/tilcdc_slave.c

@@ -298,6 +298,7 @@ static int slave_probe(struct platform_device *pdev)
 	struct tilcdc_module *mod;
 	struct pinctrl *pinctrl;
 	uint32_t i2c_phandle;
+	struct i2c_adapter *slavei2c;
 	int ret = -EINVAL;
 
 	/* bail out early if no DT data: */
@@ -306,44 +307,48 @@ static int slave_probe(struct platform_device *pdev)
 		return -ENXIO;
 	}
 
+	/* Bail out early if i2c not specified */
+	if (of_property_read_u32(node, "i2c", &i2c_phandle)) {
+		dev_err(&pdev->dev, "could not get i2c bus phandle\n");
+		return ret;
+	}
+
+	i2c_node = of_find_node_by_phandle(i2c_phandle);
+	if (!i2c_node) {
+		dev_err(&pdev->dev, "could not get i2c bus node\n");
+		return ret;
+	}
+
+	/* but defer the probe if it can't be initialized it might come later */
+	slavei2c = of_find_i2c_adapter_by_node(i2c_node);
+	of_node_put(i2c_node);
+
+	if (!slavei2c) {
+		ret = -EPROBE_DEFER;
+		tilcdc_slave_probedefer(true);
+		dev_err(&pdev->dev, "could not get i2c\n");
+		return ret;
+	}
+
 	slave_mod = kzalloc(sizeof(*slave_mod), GFP_KERNEL);
 	if (!slave_mod)
 		return -ENOMEM;
 
 	mod = &slave_mod->base;
 
+	mod->preferred_bpp = slave_info.bpp;
+
+	slave_mod->i2c = slavei2c;
+
 	tilcdc_module_init(mod, "slave", &slave_module_ops);
 
 	pinctrl = devm_pinctrl_get_select_default(&pdev->dev);
 	if (IS_ERR(pinctrl))
 		dev_warn(&pdev->dev, "pins are not configured\n");
 
-	if (of_property_read_u32(node, "i2c", &i2c_phandle)) {
-		dev_err(&pdev->dev, "could not get i2c bus phandle\n");
-		goto fail;
-	}
-
-	mod->preferred_bpp = slave_info.bpp;
-
-	i2c_node = of_find_node_by_phandle(i2c_phandle);
-	if (!i2c_node) {
-		dev_err(&pdev->dev, "could not get i2c bus node\n");
-		goto fail;
-	}
-
-	slave_mod->i2c = of_find_i2c_adapter_by_node(i2c_node);
-	if (!slave_mod->i2c) {
-		dev_err(&pdev->dev, "could not get i2c\n");
-		goto fail;
-	}
-
-	of_node_put(i2c_node);
+	tilcdc_slave_probedefer(false);
 
 	return 0;
-
-fail:
-	slave_destroy(mod);
-	return ret;
 }
 
 static int slave_remove(struct platform_device *pdev)