mt7621-qtn-rgmii: enable RGMII connected Quantenna QV840

Write a magic value to a magic destination.  This might
be specific to the Mitrastar designed ZyXEL WAP6805.

Signed-off-by: Bjørn Mork <bjorn@mork.no>

package/kernel/mt7621-qtn-rgmii/Makefile

@@ -0,0 +1,45 @@
+#
+# Copyright (C) 2020 OpenWrt.org
+#
+# This is free software, licensed under the GNU General Public License v2.
+# See /LICENSE for more information.
+#
+
+include $(TOPDIR)/rules.mk
+include $(INCLUDE_DIR)/kernel.mk
+
+PKG_NAME:=mt7621-qtn-rgmii
+PKG_RELEASE:=1
+PKG_LICENSE:=GPL-2.0
+
+PKG_MAINTAINER:=Bjørn Mork <bjorn@mork.no>
+
+include $(INCLUDE_DIR)/package.mk
+
+define KernelPackage/mt7621-qtn-rgmii
+  SECTION:=kernel
+  SUBMENU:=Other modules
+  TITLE:=Enable RGMII connected Quantenna module on MT7621
+  DEPENDS:=@TARGET_ramips_mt7621
+  HIDDEN:=1
+  FILES:=$(PKG_BUILD_DIR)/mt7621-qtn-rgmii.ko
+  AUTOLOAD:=$(call AutoLoad,30,mt7621-qtn-rgmii,1)
+endef
+
+define KernelPackage/mt7621-qtn-rgmii/description
+  Enable RGMII connected Quantenna module on MT7621.
+
+  The Mitrastar designed ZyXEL WAP6805 has a Quantenna QV840
+  module connected to the RGMII pins of the MT7621 SoC. For
+  unknown reasons, it is necessary to change the value of
+  the register at 0x1e110008 from default (usually 0xc000c)
+  to 0x9000c for this connection wo work.
+
+  This driver simply does that without much fuzz.
+endef
+
+define Build/Compile
+        $(KERNEL_MAKE) M=$(PKG_BUILD_DIR) modules
+endef
+
+$(eval $(call KernelPackage,mt7621-qtn-rgmii))

package/kernel/mt7621-qtn-rgmii/src/Makefile

@@ -0,0 +1 @@
+obj-m += mt7621-qtn-rgmii.o

package/kernel/mt7621-qtn-rgmii/src/mt7621-qtn-rgmii.c

@@ -0,0 +1,48 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (c) 2020  Bjørn Mork <bjorn@mork.no>
+ */
+#include <linux/io.h>
+#include <linux/module.h>
+
+#define MODULE_NAME "mt7621-qtn-rgmii"
+#define RGMII_REG_BASE	0x1e110008
+#define RGMII_REG_SIZE	4
+#define RGMII_REG_VALUE	0x9000c
+
+static u32 oldval;
+
+static int __init mt7621_qtn_rgmii_init(void)
+{
+	void __iomem *base = ioremap(RGMII_REG_BASE, RGMII_REG_SIZE);
+
+	if (!base)
+		return -ENOMEM;
+	oldval = ioread32(base);
+	if (oldval != RGMII_REG_VALUE) {
+		iowrite32(RGMII_REG_VALUE, base);
+		pr_info(MODULE_NAME ": changed register 0x%08x value from 0x%08x to 0x%08x\n", RGMII_REG_BASE, oldval,  RGMII_REG_VALUE);
+	}
+	iounmap(base);
+	return 0;
+}
+
+static void __exit mt7621_qtn_rgmii_exit(void)
+{
+	void __iomem *base = ioremap(RGMII_REG_BASE, RGMII_REG_SIZE);
+
+	if (!base)
+		return;
+	if (oldval != RGMII_REG_VALUE) {
+		iowrite32(oldval, base);
+		pr_info(MODULE_NAME ": reset register 0x%08x back to 0x%08x\n", RGMII_REG_BASE, oldval);
+	}
+	iounmap(base);
+}
+
+module_init(mt7621_qtn_rgmii_init);
+module_exit(mt7621_qtn_rgmii_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Bjørn Mork <bjorn@mork.no>");
+MODULE_DESCRIPTION("Enable RGMII connected Quantenna module on MT7621");