drm/ingenic: Add support for reserved memory

Add support for static memory reserved from Device Tree. Since we're
using GEM buffers backed by CMA, it is interesting to have an option to
specify the CMA area where the GEM buffers will be allocated.

v2: Don't abort probe if reserved memory cannot be obtained. The driver
    will still work fine provided the kernel configuration is sane.
Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200926170501.1109197-3-paul@crapouillou.net

drivers/gpu/drm/ingenic/ingenic-drm-drv.c

@@ -14,6 +14,7 @@
 #include <linux/module.h>
 #include <linux/mutex.h>
 #include <linux/of_device.h>
+#include <linux/of_reserved_mem.h>
 #include <linux/platform_device.h>
 #include <linux/regmap.h>
 
@@ -837,6 +838,11 @@ static void ingenic_drm_unbind_all(void *d)
 	component_unbind_all(priv->dev, &priv->drm);
 }
 
+static void __maybe_unused ingenic_drm_release_rmem(void *d)
+{
+	of_reserved_mem_device_release(d);
+}
+
 static int ingenic_drm_bind(struct device *dev, bool has_components)
 {
 	struct platform_device *pdev = to_platform_device(dev);
@@ -858,6 +864,19 @@ static int ingenic_drm_bind(struct device *dev, bool has_components)
 		return -EINVAL;
 	}
 
+	if (IS_ENABLED(CONFIG_OF_RESERVED_MEM)) {
+		ret = of_reserved_mem_device_init(dev);
+
+		if (ret && ret != -ENODEV)
+			dev_warn(dev, "Failed to get reserved memory: %d\n", ret);
+
+		if (!ret) {
+			ret = devm_add_action_or_reset(dev, ingenic_drm_release_rmem, dev);
+			if (ret)
+				return ret;
+		}
+	}
+
 	priv = devm_drm_dev_alloc(dev, &ingenic_drm_driver_data,
 				  struct ingenic_drm, drm);
 	if (IS_ERR(priv))