[PATCH v2 1/3] drm/loongson: Add a helper for creating child devices

[Sui Jingfeng <sui.jingfeng@linux.dev>]

In some display subsystems, the functionality of a PCIe device may too
complex to be managed by a single driver. A split of the functionality
into child devices can helpful to achieve better modularity.

Another benefit is that we could migrate the dependency on exterinal
modules to a submodule level with the helper created. For example, it's
not uncommon that some exterinal module will return -EPROBE_DEFER to our
driver during probe time. KMS driver has to tear down everything when it
receives -EPROBE_DEFER, the problem is that it's completely not necessary
and rising cyclic dependency problems if not process correctly.

Add the loongson_create_platform_device() function, which allows the KMS
driver to create sub-devices for it. The manually created decice acts as
agents for the principal part, migrate the potential issue to submodule.

Signed-off-by: Sui Jingfeng <sui.jingfeng@linux.dev>
---
 drivers/gpu/drm/loongson/loongson_device.c | 42 ++++++++++++++++++++++
 drivers/gpu/drm/loongson/lsdc_drv.h        |  6 ++++
 2 files changed, 48 insertions(+)

diff --git a/drivers/gpu/drm/loongson/loongson_device.c b/drivers/gpu/drm/loongson/loongson_device.c
index 9986c8a2a255..b268549d643e 100644
--- a/drivers/gpu/drm/loongson/loongson_device.c
+++ b/drivers/gpu/drm/loongson/loongson_device.c
@@ -4,6 +4,7 @@
  */
 
 #include <linux/pci.h>
+#include <linux/platform_device.h>
 
 #include "lsdc_drv.h"
 
@@ -100,3 +101,44 @@ lsdc_device_probe(struct pci_dev *pdev, enum loongson_chip_id chip_id)
 {
 	return __chip_id_desc_table[chip_id];
 }
+
+int loongson_create_platform_device(struct device *parent,
+				    const char *name, int id,
+				    struct resource *pres,
+				    void *data,
+				    struct platform_device **ppdev)
+{
+	struct platform_device *pdev;
+	int ret;
+
+	pdev = platform_device_alloc(name, id);
+	if (!pdev)
+		return -ENOMEM;
+
+	pdev->dev.parent = parent;
+
+	if (pres) {
+		ret = platform_device_add_resources(pdev, pres, 1);
+		if (ret) {
+			platform_device_put(pdev);
+			return ret;
+		}
+	}
+
+	if (data) {
+		void *pdata = kmalloc(sizeof(void *), GFP_KERNEL);
+
+		*(void **)pdata = data;
+		pdev->dev.platform_data = pdata;
+	}
+
+	ret = platform_device_add(pdev);
+	if (ret) {
+		platform_device_put(pdev);
+		return ret;
+	}
+
+	*ppdev = pdev;
+
+	return 0;
+}
diff --git a/drivers/gpu/drm/loongson/lsdc_drv.h b/drivers/gpu/drm/loongson/lsdc_drv.h
index fbf2d760ef27..a2c6b496a69f 100644
--- a/drivers/gpu/drm/loongson/lsdc_drv.h
+++ b/drivers/gpu/drm/loongson/lsdc_drv.h
@@ -47,6 +47,12 @@ enum loongson_chip_id {
 const struct lsdc_desc *
 lsdc_device_probe(struct pci_dev *pdev, enum loongson_chip_id chip);
 
+int loongson_create_platform_device(struct device *parent,
+				    const char *name, int id,
+				    struct resource *pres,
+				    void *data,
+				    struct platform_device **ppdev);
+
 struct lsdc_kms_funcs;
 
 /* DC specific */
-- 
2.34.1