[PATCH v4 2/2] soc: sprd: Add Spreadtrum special bits updating support

[Baolin Wang]

The spreadtrum platform uses a special set/clear method to update
registers' bits, which can remove the race of updating the global
registers between the multiple subsystems. Thus we can register
a physical regmap bus into syscon core to support this.

Signed-off-by: Baolin Wang <baolin.wang7@xxxxxxxxx>
---
 drivers/soc/Kconfig            |  1 +
 drivers/soc/Makefile           |  1 +
 drivers/soc/sprd/Kconfig       | 16 +++++++
 drivers/soc/sprd/Makefile      |  2 +
 drivers/soc/sprd/sprd_syscon.c | 86 ++++++++++++++++++++++++++++++++++
 5 files changed, 106 insertions(+)
 create mode 100644 drivers/soc/sprd/Kconfig
 create mode 100644 drivers/soc/sprd/Makefile
 create mode 100644 drivers/soc/sprd/sprd_syscon.c

diff --git a/drivers/soc/Kconfig b/drivers/soc/Kconfig
index 425ab6f7e375..8cfbf2dc518d 100644
--- a/drivers/soc/Kconfig
+++ b/drivers/soc/Kconfig
@@ -23,5 +23,6 @@ source "drivers/soc/versatile/Kconfig"
 source "drivers/soc/xilinx/Kconfig"
 source "drivers/soc/zte/Kconfig"
 source "drivers/soc/kendryte/Kconfig"
+source "drivers/soc/sprd/Kconfig"
 
 endmenu
diff --git a/drivers/soc/Makefile b/drivers/soc/Makefile
index 36452bed86ef..7d156a6dd536 100644
--- a/drivers/soc/Makefile
+++ b/drivers/soc/Makefile
@@ -29,3 +29,4 @@ obj-$(CONFIG_PLAT_VERSATILE)	+= versatile/
 obj-y				+= xilinx/
 obj-$(CONFIG_ARCH_ZX)		+= zte/
 obj-$(CONFIG_SOC_KENDRYTE)	+= kendryte/
+obj-$(CONFIG_ARCH_SPRD)		+= sprd/
diff --git a/drivers/soc/sprd/Kconfig b/drivers/soc/sprd/Kconfig
new file mode 100644
index 000000000000..38d1f5971a28
--- /dev/null
+++ b/drivers/soc/sprd/Kconfig
@@ -0,0 +1,16 @@
+# SPDX-License-Identifier: GPL-2.0-only
+#
+# SPRD SoC drivers
+#
+
+menu "Spreadtrum SoC drivers"
+	depends on ARCH_SPRD || COMPILE_TEST
+
+config SPRD_SYSCON
+	tristate "Spreadtrum syscon support"
+	depends on ARCH_SPRD || COMPILE_TEST
+	help
+	  Say yes here to add support for the Spreadtrum syscon driver,
+	  which is used to implement the atomic method of bits updating.
+
+endmenu
diff --git a/drivers/soc/sprd/Makefile b/drivers/soc/sprd/Makefile
new file mode 100644
index 000000000000..4d7715553cf6
--- /dev/null
+++ b/drivers/soc/sprd/Makefile
@@ -0,0 +1,2 @@
+# SPDX-License-Identifier: GPL-2.0-only
+obj-$(CONFIG_SPRD_SYSCON) += sprd_syscon.o
diff --git a/drivers/soc/sprd/sprd_syscon.c b/drivers/soc/sprd/sprd_syscon.c
new file mode 100644
index 000000000000..cdc326ef94e5
--- /dev/null
+++ b/drivers/soc/sprd/sprd_syscon.c
@@ -0,0 +1,86 @@
+//SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2020 Spreadtrum Communications Inc.
+ */
+#include <linux/io.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/mfd/syscon.h>
+#include <linux/of.h>
+#include <linux/regmap.h>
+
+#define SPRD_REG_SET_OFFSET	0x1000
+#define SPRD_REG_CLR_OFFSET	0x2000
+
+/*
+ * The Spreadtrum platform defines a special set/clear method to update
+ * registers' bits, which means it can write values to the register's SET
+ * address (offset is 0x1000) to set bits, and write values to the register's
+ * CLEAR address (offset is 0x2000) to clear bits.
+ *
+ * This set/clear method can help to remove the race of accessing the global
+ * registers between the multiple subsystems instead of using hardware
+ * spinlocks.
+ *
+ * Note: there is a potential risk when users want to set and clear bits
+ * at the same time, since the set/clear method will always do bits setting
+ * before bits clearing, which may cause some unexpected results if the
+ * operation sequence is strict. Thus we recommend that do not set and
+ * clear bits at the same time if you are not sure about the results.
+ */
+static int sprd_syscon_update_bits(void *context, unsigned int reg,
+				   unsigned int mask, unsigned int val)
+{
+	void __iomem *base = context;
+	unsigned int set, clr;
+
+	set = val & mask;
+	clr = ~set & mask;
+
+	if (set)
+		writel(set, base + reg + SPRD_REG_SET_OFFSET);
+
+	if (clr)
+		writel(clr, base + reg + SPRD_REG_CLR_OFFSET);
+
+	WARN_ONCE(set && clr, "%s: non-atomic update", __func__);
+	return 0;
+}
+
+static int sprd_syscon_read(void *context, unsigned int reg, unsigned int *val)
+{
+	void __iomem *base = context;
+
+	*val = readl(base + reg);
+	return 0;
+}
+
+static int sprd_syscon_write(void *context, unsigned int reg, unsigned int val)
+{
+	void __iomem *base = context;
+
+	writel(val, base + reg);
+	return 0;
+}
+
+static struct regmap_bus sprd_syscon_regmap = {
+	.fast_io = true,
+	.reg_write = sprd_syscon_write,
+	.reg_read = sprd_syscon_read,
+	.reg_update_bits = sprd_syscon_update_bits,
+	.val_format_endian_default = REGMAP_ENDIAN_LITTLE,
+};
+
+struct regmap *syscon_regmap_init(struct device_node *np, void __iomem *base,
+				  struct regmap_config *syscon_config)
+{
+	if (of_device_is_compatible(np, "sprd,atomic-syscon"))
+		return regmap_init(NULL, &sprd_syscon_regmap, base,
+				   syscon_config);
+
+	return regmap_init_mmio(NULL, base, syscon_config);
+}
+
+MODULE_DESCRIPTION("Spreadtrum syscon support");
+MODULE_AUTHOR("Baolin Wang <baolin.wang@xxxxxxxxxx>");
+MODULE_LICENSE("GPL v2");
-- 
2.17.1