drivers/soc/litex: add LiteX SoC Controller driver

This commit adds driver for the FPGA-based LiteX SoC
Controller from LiteX SoC builder.

Co-developed-by: Mateusz Holenko <mholenko@antmicro.com>
Signed-off-by: Mateusz Holenko <mholenko@antmicro.com>
Signed-off-by: Pawel Czarnecki <pczarnecki@internships.antmicro.com>
Signed-off-by: Stafford Horne <shorne@gmail.com>

MAINTAINERS

@@ -10177,6 +10177,8 @@ M:	Karol Gugala <kgugala@antmicro.com>
 M:	Mateusz Holenko <mholenko@antmicro.com>
 S:	Maintained
 F:	Documentation/devicetree/bindings/*/litex,*.yaml
+F:	drivers/soc/litex/litex_soc_ctrl.c
+F:	include/linux/litex.h
 
 LIVE PATCHING
 M:	Josh Poimboeuf <jpoimboe@redhat.com>

drivers/soc/Kconfig

@@ -9,6 +9,7 @@ source "drivers/soc/bcm/Kconfig"
 source "drivers/soc/fsl/Kconfig"
 source "drivers/soc/imx/Kconfig"
 source "drivers/soc/ixp4xx/Kconfig"
+source "drivers/soc/litex/Kconfig"
 source "drivers/soc/mediatek/Kconfig"
 source "drivers/soc/qcom/Kconfig"
 source "drivers/soc/renesas/Kconfig"

drivers/soc/Makefile

@@ -14,6 +14,7 @@ obj-$(CONFIG_ARCH_GEMINI)	+= gemini/
 obj-y				+= imx/
 obj-$(CONFIG_ARCH_IXP4XX)	+= ixp4xx/
 obj-$(CONFIG_SOC_XWAY)		+= lantiq/
+obj-$(CONFIG_LITEX_SOC_CONTROLLER) += litex/
 obj-y				+= mediatek/
 obj-y				+= amlogic/
 obj-y				+= qcom/

drivers/soc/litex/Kconfig

@@ -0,0 +1,19 @@
+# SPDX-License_Identifier: GPL-2.0
+
+menu "Enable LiteX SoC Builder specific drivers"
+
+config LITEX
+	bool
+
+config LITEX_SOC_CONTROLLER
+	tristate "Enable LiteX SoC Controller driver"
+	depends on OF || COMPILE_TEST
+	select LITEX
+	help
+	  This option enables the SoC Controller Driver which verifies
+	  LiteX CSR access and provides common litex_get_reg/litex_set_reg
+	  accessors.
+	  All drivers that use functions from litex.h must depend on
+	  LITEX.
+
+endmenu

drivers/soc/litex/Makefile

@@ -0,0 +1,3 @@
+# SPDX-License_Identifier: GPL-2.0
+
+obj-$(CONFIG_LITEX_SOC_CONTROLLER)	+= litex_soc_ctrl.o

drivers/soc/litex/litex_soc_ctrl.c

@@ -0,0 +1,176 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * LiteX SoC Controller Driver
+ *
+ * Copyright (C) 2020 Antmicro <www.antmicro.com>
+ *
+ */
+
+#include <linux/litex.h>
+#include <linux/device.h>
+#include <linux/errno.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+#include <linux/printk.h>
+#include <linux/module.h>
+#include <linux/errno.h>
+#include <linux/io.h>
+
+/*
+ * LiteX SoC Generator, depending on the configuration, can split a single
+ * logical CSR (Control&Status Register) into a series of consecutive physical
+ * registers.
+ *
+ * For example, in the configuration with 8-bit CSR Bus, 32-bit aligned (the
+ * default one for 32-bit CPUs) a 32-bit logical CSR will be generated as four
+ * 32-bit physical registers, each one containing one byte of meaningful data.
+ *
+ * For details see: https://github.com/enjoy-digital/litex/wiki/CSR-Bus
+ *
+ * The purpose of `litex_set_reg`/`litex_get_reg` is to implement the logic
+ * of writing to/reading from the LiteX CSR in a single place that can be
+ * then reused by all LiteX drivers.
+ */
+
+/**
+ * litex_set_reg() - Writes the value to the LiteX CSR (Control&Status Register)
+ * @reg: Address of the CSR
+ * @reg_size: The width of the CSR expressed in the number of bytes
+ * @val: Value to be written to the CSR
+ *
+ * In the currently supported LiteX configuration (8-bit CSR Bus, 32-bit aligned),
+ * a 32-bit LiteX CSR is generated as 4 consecutive 32-bit physical registers,
+ * each one containing one byte of meaningful data.
+ *
+ * This function splits a single possibly multi-byte write into a series of
+ * single-byte writes with a proper offset.
+ */
+void litex_set_reg(void __iomem *reg, unsigned long reg_size,
+		    unsigned long val)
+{
+	unsigned long shifted_data, shift, i;
+
+	for (i = 0; i < reg_size; ++i) {
+		shift = ((reg_size - i - 1) * LITEX_SUBREG_SIZE_BIT);
+		shifted_data = val >> shift;
+
+		WRITE_LITEX_SUBREGISTER(shifted_data, reg, i);
+	}
+}
+EXPORT_SYMBOL_GPL(litex_set_reg);
+
+/**
+ * litex_get_reg() - Reads the value of the LiteX CSR (Control&Status Register)
+ * @reg: Address of the CSR
+ * @reg_size: The width of the CSR expressed in the number of bytes
+ *
+ * Return: Value read from the CSR
+ *
+ * In the currently supported LiteX configuration (8-bit CSR Bus, 32-bit aligned),
+ * a 32-bit LiteX CSR is generated as 4 consecutive 32-bit physical registers,
+ * each one containing one byte of meaningful data.
+ *
+ * This function generates a series of single-byte reads with a proper offset
+ * and joins their results into a single multi-byte value.
+ */
+unsigned long litex_get_reg(void __iomem *reg, unsigned long reg_size)
+{
+	unsigned long shifted_data, shift, i;
+	unsigned long result = 0;
+
+	for (i = 0; i < reg_size; ++i) {
+		shifted_data = READ_LITEX_SUBREGISTER(reg, i);
+
+		shift = ((reg_size - i - 1) * LITEX_SUBREG_SIZE_BIT);
+		result |= (shifted_data << shift);
+	}
+
+	return result;
+}
+EXPORT_SYMBOL_GPL(litex_get_reg);
+
+#define SCRATCH_REG_OFF         0x04
+#define SCRATCH_REG_VALUE       0x12345678
+#define SCRATCH_TEST_VALUE      0xdeadbeef
+
+/*
+ * Check LiteX CSR read/write access
+ *
+ * This function reads and writes a scratch register in order to verify if CSR
+ * access works.
+ *
+ * In case any problems are detected, the driver should panic.
+ *
+ * Access to the LiteX CSR is, by design, done in CPU native endianness.
+ * The driver should not dynamically configure access functions when
+ * the endianness mismatch is detected. Such situation indicates problems in
+ * the soft SoC design and should be solved at the LiteX generator level,
+ * not in the software.
+ */
+static int litex_check_csr_access(void __iomem *reg_addr)
+{
+	unsigned long reg;
+
+	reg = litex_read32(reg_addr + SCRATCH_REG_OFF);
+
+	if (reg != SCRATCH_REG_VALUE) {
+		panic("Scratch register read error - the system is probably broken! Expected: 0x%x but got: 0x%lx",
+			SCRATCH_REG_VALUE, reg);
+		return -EINVAL;
+	}
+
+	litex_write32(reg_addr + SCRATCH_REG_OFF, SCRATCH_TEST_VALUE);
+	reg = litex_read32(reg_addr + SCRATCH_REG_OFF);
+
+	if (reg != SCRATCH_TEST_VALUE) {
+		panic("Scratch register write error - the system is probably broken! Expected: 0x%x but got: 0x%lx",
+			SCRATCH_TEST_VALUE, reg);
+		return -EINVAL;
+	}
+
+	/* restore original value of the SCRATCH register */
+	litex_write32(reg_addr + SCRATCH_REG_OFF, SCRATCH_REG_VALUE);
+
+	pr_info("LiteX SoC Controller driver initialized");
+
+	return 0;
+}
+
+struct litex_soc_ctrl_device {
+	void __iomem *base;
+};
+
+static const struct of_device_id litex_soc_ctrl_of_match[] = {
+	{.compatible = "litex,soc-controller"},
+	{},
+};
+
+MODULE_DEVICE_TABLE(of, litex_soc_ctrl_of_match);
+
+static int litex_soc_ctrl_probe(struct platform_device *pdev)
+{
+	struct litex_soc_ctrl_device *soc_ctrl_dev;
+
+	soc_ctrl_dev = devm_kzalloc(&pdev->dev, sizeof(*soc_ctrl_dev), GFP_KERNEL);
+	if (!soc_ctrl_dev)
+		return -ENOMEM;
+
+	soc_ctrl_dev->base = devm_platform_ioremap_resource(pdev, 0);
+	if (IS_ERR(soc_ctrl_dev->base))
+		return PTR_ERR(soc_ctrl_dev->base);
+
+	return litex_check_csr_access(soc_ctrl_dev->base);
+}
+
+static struct platform_driver litex_soc_ctrl_driver = {
+	.driver = {
+		.name = "litex-soc-controller",
+		.of_match_table = of_match_ptr(litex_soc_ctrl_of_match)
+	},
+	.probe = litex_soc_ctrl_probe,
+};
+
+module_platform_driver(litex_soc_ctrl_driver);
+MODULE_DESCRIPTION("LiteX SoC Controller driver");
+MODULE_AUTHOR("Antmicro <www.antmicro.com>");
+MODULE_LICENSE("GPL v2");

include/linux/litex.h

@@ -0,0 +1,102 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Common LiteX header providing
+ * helper functions for accessing CSRs.
+ *
+ * Implementation of the functions is provided by
+ * the LiteX SoC Controller driver.
+ *
+ * Copyright (C) 2019-2020 Antmicro <www.antmicro.com>
+ */
+
+#ifndef _LINUX_LITEX_H
+#define _LINUX_LITEX_H
+
+#include <linux/io.h>
+#include <linux/types.h>
+#include <linux/compiler_types.h>
+
+/*
+ * The parameters below are true for LiteX SoCs configured for 8-bit CSR Bus,
+ * 32-bit aligned.
+ *
+ * Supporting other configurations will require extending the logic in this
+ * header and in the LiteX SoC controller driver.
+ */
+#define LITEX_REG_SIZE	  0x4
+#define LITEX_SUBREG_SIZE	0x1
+#define LITEX_SUBREG_SIZE_BIT	 (LITEX_SUBREG_SIZE * 8)
+
+#define WRITE_LITEX_SUBREGISTER(val, base_offset, subreg_id) \
+	writel((u32 __force)cpu_to_le32(val), base_offset + (LITEX_REG_SIZE * subreg_id))
+
+#define READ_LITEX_SUBREGISTER(base_offset, subreg_id) \
+	le32_to_cpu((__le32 __force)readl(base_offset + (LITEX_REG_SIZE * subreg_id)))
+
+void litex_set_reg(void __iomem *reg, unsigned long reg_sz, unsigned long val);
+
+unsigned long litex_get_reg(void __iomem *reg, unsigned long reg_sz);
+
+static inline void litex_write8(void __iomem *reg, u8 val)
+{
+	WRITE_LITEX_SUBREGISTER(val, reg, 0);
+}
+
+static inline void litex_write16(void __iomem *reg, u16 val)
+{
+	WRITE_LITEX_SUBREGISTER(val >> 8, reg, 0);
+	WRITE_LITEX_SUBREGISTER(val, reg, 1);
+}
+
+static inline void litex_write32(void __iomem *reg, u32 val)
+{
+	WRITE_LITEX_SUBREGISTER(val >> 24, reg, 0);
+	WRITE_LITEX_SUBREGISTER(val >> 16, reg, 1);
+	WRITE_LITEX_SUBREGISTER(val >> 8, reg, 2);
+	WRITE_LITEX_SUBREGISTER(val, reg, 3);
+}
+
+static inline void litex_write64(void __iomem *reg, u64 val)
+{
+	WRITE_LITEX_SUBREGISTER(val >> 56, reg, 0);
+	WRITE_LITEX_SUBREGISTER(val >> 48, reg, 1);
+	WRITE_LITEX_SUBREGISTER(val >> 40, reg, 2);
+	WRITE_LITEX_SUBREGISTER(val >> 32, reg, 3);
+	WRITE_LITEX_SUBREGISTER(val >> 24, reg, 4);
+	WRITE_LITEX_SUBREGISTER(val >> 16, reg, 5);
+	WRITE_LITEX_SUBREGISTER(val >> 8, reg, 6);
+	WRITE_LITEX_SUBREGISTER(val, reg, 7);
+}
+
+static inline u8 litex_read8(void __iomem *reg)
+{
+	return READ_LITEX_SUBREGISTER(reg, 0);
+}
+
+static inline u16 litex_read16(void __iomem *reg)
+{
+	return (READ_LITEX_SUBREGISTER(reg, 0) << 8)
+		| (READ_LITEX_SUBREGISTER(reg, 1));
+}
+
+static inline u32 litex_read32(void __iomem *reg)
+{
+	return (READ_LITEX_SUBREGISTER(reg, 0) << 24)
+		| (READ_LITEX_SUBREGISTER(reg, 1) << 16)
+		| (READ_LITEX_SUBREGISTER(reg, 2) << 8)
+		| (READ_LITEX_SUBREGISTER(reg, 3));
+}
+
+static inline u64 litex_read64(void __iomem *reg)
+{
+	return ((u64)READ_LITEX_SUBREGISTER(reg, 0) << 56)
+		| ((u64)READ_LITEX_SUBREGISTER(reg, 1) << 48)
+		| ((u64)READ_LITEX_SUBREGISTER(reg, 2) << 40)
+		| ((u64)READ_LITEX_SUBREGISTER(reg, 3) << 32)
+		| ((u64)READ_LITEX_SUBREGISTER(reg, 4) << 24)
+		| ((u64)READ_LITEX_SUBREGISTER(reg, 5) << 16)
+		| ((u64)READ_LITEX_SUBREGISTER(reg, 6) << 8)
+		| ((u64)READ_LITEX_SUBREGISTER(reg, 7));
+}
+
+#endif /* _LINUX_LITEX_H */