bus: add bus driver for accessing Allwinner A64 DE2

The "Display Engine 2.0" (usually called DE2) on the Allwinner A64 SoC
is different from the ones on other Allwinner SoCs. It requires a SRAM
region to be claimed, otherwise all DE2 subblocks won't be accessible.

Add a bus driver for the Allwinner A64 DE2 part which claims the SRAM
region when probing.

Signed-off-by: Icenowy Zheng <[e-mail]>
Signed-off-by: Maxime Ripard <[e-mail]>

drivers/bus/Kconfig

···
 	  Controller (BSC, sometimes called "LBSC within Bus Bridge", or
 	  "External Bus Interface") as found on several Renesas ARM SoCs.
 
+config SUN50I_DE2_BUS
+	bool "Allwinner A64 DE2 Bus Driver"
+	  default ARM64
+	  depends on ARCH_SUNXI
+	  select SUNXI_SRAM
+	  help
+	  Say y here to enable support for Allwinner A64 DE2 bus driver. It's
+	  mostly transparent, but a SRAM region needs to be claimed in the SRAM
+	  controller to make the all blocks in the DE2 part accessible.
+
 config SUNXI_RSB
 	tristate "Allwinner sunXi Reduced Serial Bus Driver"
 	  default MACH_SUN8I || MACH_SUN9I || ARM64

drivers/bus/Makefile

···
 
 obj-$(CONFIG_OMAP_OCP2SCP)	+= omap-ocp2scp.o
 obj-$(CONFIG_QCOM_EBI2)		+= qcom-ebi2.o
+obj-$(CONFIG_SUN50I_DE2_BUS)	+= sun50i-de2.o
 obj-$(CONFIG_SUNXI_RSB)		+= sunxi-rsb.o
 obj-$(CONFIG_SIMPLE_PM_BUS)	+= simple-pm-bus.o
 obj-$(CONFIG_TEGRA_ACONNECT)	+= tegra-aconnect.o

drivers/bus/sun50i-de2.c

···
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Allwinner A64 Display Engine 2.0 Bus Driver
+ *
+ * Copyright (C) 2018 Icenowy Zheng <[e-mail]>
+ */
+
+#include <linux/of_platform.h>
+#include <linux/platform_device.h>
+#include <linux/soc/sunxi/sunxi_sram.h>
+
+static int sun50i_de2_bus_probe(struct platform_device *pdev)
+{
+	struct device_node *np = pdev->dev.of_node;
+	int ret;
+
+	ret = sunxi_sram_claim(&pdev->dev);
+	if (ret) {
+		dev_err(&pdev->dev, "Error couldn't map SRAM to device\n");
+		return ret;
+	}
+
+	of_platform_populate(np, NULL, NULL, &pdev->dev);
+
+	return 0;
+}
+
+static int sun50i_de2_bus_remove(struct platform_device *pdev)
+{
+	sunxi_sram_release(&pdev->dev);
+	return 0;
+}
+
+static const struct of_device_id sun50i_de2_bus_of_match[] = {
+	{ .compatible = "allwinner,sun50i-a64-de2", },
+	{ /* sentinel */ }
+};
+
+static struct platform_driver sun50i_de2_bus_driver = {
+	.probe = sun50i_de2_bus_probe,
+	.remove = sun50i_de2_bus_remove,
+	.driver = {
+		.name = "sun50i-de2-bus",
+		.of_match_table = sun50i_de2_bus_of_match,
+	},
+};
+
+builtin_platform_driver(sun50i_de2_bus_driver);