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Subject[PATCH v6 3/5] drivers/soc/litex: add LiteX SoC Controller driver
From: Pawel Czarnecki <pczarnecki@internships.antmicro.com>

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>
---

Notes:
Changes in v6:
- added dependency on OF || COMPILE_TEST
- used le32_to_cpu(readl(addr)) instead of __raw_readl
and writel(cpu_to_le32(value), addr) instead of __raw_writel
to take advantage of memory barriers provided by readl/writel

Changes in v5:
- removed helper accessors and used __raw_readl/__raw_writel instead
- fixed checking for errors in litex_soc_ctrl_probe

Changes in v4:
- fixed indent in Kconfig's help section
- fixed copyright header
- changed compatible to "litex,soc-controller"
- simplified litex_soc_ctrl_probe
- removed unnecessary litex_soc_ctrl_remove

This commit has been introduced in v3 of the patchset.

It includes a simplified version of common 'litex.h'
header introduced in v2 of the patchset.

MAINTAINERS | 2 +
drivers/soc/Kconfig | 1 +
drivers/soc/Makefile | 1 +
drivers/soc/litex/Kconfig | 15 +++
drivers/soc/litex/Makefile | 3 +
drivers/soc/litex/litex_soc_ctrl.c | 197 +++++++++++++++++++++++++++++
include/linux/litex.h | 45 +++++++
7 files changed, 264 insertions(+)
create mode 100644 drivers/soc/litex/Kconfig
create mode 100644 drivers/soc/litex/Makefile
create mode 100644 drivers/soc/litex/litex_soc_ctrl.c
create mode 100644 include/linux/litex.h

diff --git a/MAINTAINERS b/MAINTAINERS
index 39be98db7418..4d70a1b22a87 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -9840,6 +9840,8 @@ 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>
diff --git a/drivers/soc/Kconfig b/drivers/soc/Kconfig
index 425ab6f7e375..d097d070f579 100644
--- a/drivers/soc/Kconfig
+++ b/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"
diff --git a/drivers/soc/Makefile b/drivers/soc/Makefile
index 36452bed86ef..0b16108823ef 100644
--- a/drivers/soc/Makefile
+++ b/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/
diff --git a/drivers/soc/litex/Kconfig b/drivers/soc/litex/Kconfig
new file mode 100644
index 000000000000..c974ec3846bc
--- /dev/null
+++ b/drivers/soc/litex/Kconfig
@@ -0,0 +1,15 @@
+# SPDX-License_Identifier: GPL-2.0
+
+menu "Enable LiteX SoC Builder specific drivers"
+
+config LITEX_SOC_CONTROLLER
+ tristate "Enable LiteX SoC Controller driver"
+ depends on OF || COMPILE_TEST
+ 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_SOC_CONTROLLER.
+
+endmenu
diff --git a/drivers/soc/litex/Makefile b/drivers/soc/litex/Makefile
new file mode 100644
index 000000000000..98ff7325b1c0
--- /dev/null
+++ b/drivers/soc/litex/Makefile
@@ -0,0 +1,3 @@
+# SPDX-License_Identifier: GPL-2.0
+
+obj-$(CONFIG_LITEX_SOC_CONTROLLER) += litex_soc_ctrl.o
diff --git a/drivers/soc/litex/litex_soc_ctrl.c b/drivers/soc/litex/litex_soc_ctrl.c
new file mode 100644
index 000000000000..319be92fc63f
--- /dev/null
+++ b/drivers/soc/litex/litex_soc_ctrl.c
@@ -0,0 +1,197 @@
+// 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/of_platform.h>
+#include <linux/platform_device.h>
+#include <linux/printk.h>
+#include <linux/module.h>
+#include <linux/errno.h>
+#include <linux/io.h>
+
+/*
+ * The parameters below are true for LiteX SoC
+ * configured for 8-bit CSR Bus, 32-bit aligned.
+ *
+ * Supporting other configurations will require
+ * extending the logic in this header.
+ */
+#define LITEX_REG_SIZE 0x4
+#define LITEX_SUBREG_SIZE 0x1
+#define LITEX_SUBREG_SIZE_BIT (LITEX_SUBREG_SIZE * 8)
+
+static DEFINE_SPINLOCK(csr_lock);
+
+/*
+ * 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.
+ */
+void litex_set_reg(void __iomem *reg, unsigned long reg_size,
+ unsigned long val)
+{
+ unsigned long shifted_data, shift, i;
+ unsigned long flags;
+
+ spin_lock_irqsave(&csr_lock, flags);
+
+ for (i = 0; i < reg_size; ++i) {
+ shift = ((reg_size - i - 1) * LITEX_SUBREG_SIZE_BIT);
+ shifted_data = val >> shift;
+
+ writel(cpu_to_le32(shifted_data), reg + (LITEX_REG_SIZE * i));
+ }
+
+ spin_unlock_irqrestore(&csr_lock, flags);
+}
+
+unsigned long litex_get_reg(void __iomem *reg, unsigned long reg_size)
+{
+ unsigned long shifted_data, shift, i;
+ unsigned long result = 0;
+ unsigned long flags;
+
+ spin_lock_irqsave(&csr_lock, flags);
+
+ for (i = 0; i < reg_size; ++i) {
+ shifted_data = le32_to_cpu(readl(reg + (LITEX_REG_SIZE * i)));
+
+ shift = ((reg_size - i - 1) * LITEX_SUBREG_SIZE_BIT);
+ result |= (shifted_data << shift);
+ }
+
+ spin_unlock_irqrestore(&csr_lock, flags);
+
+ return result;
+}
+
+static int accessors_ok;
+
+/*
+ * Check if accessors are safe to be used by other drivers
+ * returns true if yes - false if not
+ */
+int litex_check_accessors(void)
+{
+ return accessors_ok;
+}
+
+#define SCRATCH_REG_OFF 0x04
+#define SCRATCH_REG_SIZE 4
+#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
+ * and not set `accessors_ok` flag. As a result no other
+ * LiteX driver should access CSR bus.
+ *
+ * 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_get_reg(reg_addr + SCRATCH_REG_OFF, SCRATCH_REG_SIZE);
+
+ if (reg != SCRATCH_REG_VALUE) {
+ panic("Scratch register read error! Expected: 0x%x but got: 0x%lx",
+ SCRATCH_REG_VALUE, reg);
+ return -EINVAL;
+ }
+
+ litex_set_reg(reg_addr + SCRATCH_REG_OFF,
+ SCRATCH_REG_SIZE, SCRATCH_TEST_VALUE);
+ reg = litex_get_reg(reg_addr + SCRATCH_REG_OFF, SCRATCH_REG_SIZE);
+
+ if (reg != SCRATCH_TEST_VALUE) {
+ panic("Scratch register write error! Expected: 0x%x but got: 0x%lx",
+ SCRATCH_TEST_VALUE, reg);
+ return -EINVAL;
+ }
+
+ /* restore original value of the SCRATCH register */
+ litex_set_reg(reg_addr + SCRATCH_REG_OFF,
+ SCRATCH_REG_SIZE, SCRATCH_REG_VALUE);
+
+ /* Set flag for other drivers */
+ accessors_ok = 1;
+ 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 device *dev;
+ struct device_node *node;
+ struct litex_soc_ctrl_device *soc_ctrl_dev;
+
+ dev = &pdev->dev;
+ node = dev->of_node;
+ if (!node)
+ return -ENODEV;
+
+ soc_ctrl_dev = devm_kzalloc(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");
diff --git a/include/linux/litex.h b/include/linux/litex.h
new file mode 100644
index 000000000000..f31062436273
--- /dev/null
+++ b/include/linux/litex.h
@@ -0,0 +1,45 @@
+/* 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>
+
+/*
+ * litex_check_accessors is a function implemented in
+ * drivers/soc/litex/litex_soc_controller.c
+ * checking if the common LiteX CSR accessors
+ * are safe to be used by the drivers;
+ * returns true (1) if yes - false (0) if not
+ *
+ * Important: All drivers that use litex_set_reg/litex_get_reg
+ * functions should make sure that LiteX SoC Controller driver
+ * has verified LiteX CSRs read and write operations before
+ * issuing any read/writes to the LiteX peripherals.
+ *
+ * Exemplary snippet that can be used at the beginning
+ * of the driver's probe() function to ensure that LiteX
+ * SoC Controller driver is properely initialized:
+ *
+ * if (!litex_check_accessors())
+ * return -EPROBE_DEFER;
+ */
+int litex_check_accessors(void);
+
+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);
+
+
+#endif /* _LINUX_LITEX_H */
--
2.25.1
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