[PATCH v3 5/6] bus: Add Baikal-T1 APB-bus driver

[Serge Semin <Sergey.Semin@baikalelectronics.ru>]

Baikal-T1 AXI-APB bridge is used to access the SoC subsystem CSRs.
IO requests are routed to this bus by means of the DW AMBA 3 AXI
Interconnect. In case if an attempted APB transaction stays with no
response for a pre-defined time an interrupt occurs and the bus gets
freed for a next operation. This driver provides the interrupt handler
to detect the erroneous address, prints an error message about the
address fault, updates an errors counter. The counter and the APB-bus
operations timeout can be accessed via corresponding sysfs nodes.
A dedicated sysfs-node can be also used to artificially cause the
bus errors described above.

Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Cc: Alexey Malahov <Alexey.Malahov@baikalelectronics.ru>
Cc: Paul Burton <paulburton@kernel.org>
Cc: Olof Johansson <olof@lixom.net>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: linux-mips@vger.kernel.org
Cc: soc@kernel.org
Cc: devicetree@vger.kernel.org

---

Changelog v2:
- Fix commit message and Kconfig help text spelling.
- Move driver from soc to the bus subsystem.
- Convert a simple EHB driver to the Baikal-T1 AXI-bus one.
- Convert registers MMIO to the regmap.
- Add reset line support.
- Remove probe-status info string printout.
- Since the driver depends on the OF config we can remove of_match_ptr()
  macro utilization.
- Don't print error-message if no platform IRQ found. Just return an error.

Changelog v3:
- Discard CONFIG_OF dependency since there is none at compile-time.
---
 drivers/bus/Kconfig   |  15 ++
 drivers/bus/Makefile  |   1 +
 drivers/bus/bt1-apb.c | 421 ++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 437 insertions(+)
 create mode 100644 drivers/bus/bt1-apb.c

diff --git a/drivers/bus/Kconfig b/drivers/bus/Kconfig
index 1080dd26e268..030f0e59f193 100644
--- a/drivers/bus/Kconfig
+++ b/drivers/bus/Kconfig
@@ -29,6 +29,21 @@ config BRCMSTB_GISB_ARB
 	  arbiter. This driver provides timeout and target abort error handling
 	  and internal bus master decoding.
 
+config BT1_APB
+	tristate "Baikal-T1 APB-bus driver"
+	depends on MIPS_BAIKAL_T1 || COMPILE_TEST
+	select REGMAP_MMIO
+	help
+	  Baikal-T1 AXI-APB bridge is used to access the SoC subsystem CSRs.
+	  IO requests are routed to this bus by means of the DW AMBA 3 AXI
+	  Interconnect. In case of any APB protocol collisions, slave device
+	  not responding on timeout an IRQ is raised with an erroneous address
+	  reported to the APB terminator (APB Errors Handler Block). This
+	  driver provides the interrupt handler to detect the erroneous
+	  address, prints an error message about the address fault, updates an
+	  errors counter. The counter and the APB-bus operations timeout can be
+	  accessed via corresponding sysfs nodes.
+
 config BT1_AXI
 	tristate "Baikal-T1 AXI-bus driver"
 	depends on MIPS_BAIKAL_T1 || COMPILE_TEST
diff --git a/drivers/bus/Makefile b/drivers/bus/Makefile
index eaa25d171ebd..08ccbfaf7705 100644
--- a/drivers/bus/Makefile
+++ b/drivers/bus/Makefile
@@ -13,6 +13,7 @@ obj-$(CONFIG_MOXTET)		+= moxtet.o
 # DPAA2 fsl-mc bus
 obj-$(CONFIG_FSL_MC_BUS)	+= fsl-mc/
 
+obj-$(CONFIG_BT1_APB)		+= bt1-apb.o
 obj-$(CONFIG_BT1_AXI)		+= bt1-axi.o
 obj-$(CONFIG_IMX_WEIM)		+= imx-weim.o
 obj-$(CONFIG_MIPS_CDMM)		+= mips_cdmm.o
diff --git a/drivers/bus/bt1-apb.c b/drivers/bus/bt1-apb.c
new file mode 100644
index 000000000000..295cfa83aa23
--- /dev/null
+++ b/drivers/bus/bt1-apb.c
@@ -0,0 +1,421 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2020 BAIKAL ELECTRONICS, JSC
+ *
+ * Authors:
+ *   Serge Semin <Sergey.Semin@baikalelectronics.ru>
+ *
+ * Baikal-T1 APB-bus driver
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/types.h>
+#include <linux/device.h>
+#include <linux/atomic.h>
+#include <linux/platform_device.h>
+#include <linux/interrupt.h>
+#include <linux/nmi.h>
+#include <linux/regmap.h>
+#include <linux/clk.h>
+#include <linux/reset.h>
+#include <linux/time64.h>
+#include <linux/clk.h>
+#include <linux/sysfs.h>
+
+#define APB_EHB_ISR			0x00
+#define APB_EHB_ISR_PENDING		BIT(0)
+#define APB_EHB_ISR_MASK		BIT(1)
+#define APB_EHB_ADDR			0x04
+#define APB_EHB_TIMEOUT			0x08
+
+#define APB_EHB_TIMEOUT_MIN		0x000003FFU
+#define APB_EHB_TIMEOUT_MAX		0xFFFFFFFFU
+
+/*
+ * struct bt1_apb - Baikal-T1 APB EHB private data
+ * @dev: Pointer to the device structure.
+ * @regs: APB EHB registers map.
+ * @res: No-device error injection memory region.
+ * @irq: Errors IRQ number.
+ * @rate: APB-bus reference clock rate.
+ * @pclk: APB-reference clock.
+ * @prst: APB domain reset line.
+ * @count: Number of errors detected.
+ */
+struct bt1_apb {
+	struct device *dev;
+
+	struct regmap *regs;
+	void __iomem *res;
+	int irq;
+
+	unsigned long rate;
+	struct clk *pclk;
+
+	struct reset_control *prst;
+
+	atomic_t count;
+};
+
+static const struct regmap_config bt1_apb_regmap_cfg = {
+	.reg_bits = 32,
+	.val_bits = 32,
+	.reg_stride = 4,
+	.max_register = APB_EHB_TIMEOUT,
+	.fast_io = true
+};
+
+static inline unsigned long bt1_apb_n_to_timeout_us(struct bt1_apb *apb, u32 n)
+{
+	u64 timeout = (u64)n * USEC_PER_SEC;
+
+	do_div(timeout, apb->rate);
+
+	return timeout;
+
+}
+
+static inline unsigned long bt1_apb_timeout_to_n_us(struct bt1_apb *apb,
+						    unsigned long timeout)
+{
+	u64 n = (u64)timeout * apb->rate;
+
+	do_div(n, USEC_PER_SEC);
+
+	return n;
+
+}
+
+static irqreturn_t bt1_apb_isr(int irq, void *data)
+{
+	struct bt1_apb *apb = data;
+	u32 addr = 0;
+
+	regmap_read(apb->regs, APB_EHB_ADDR, &addr);
+
+	dev_crit_ratelimited(apb->dev,
+		"APB-bus fault %d: Slave access timeout at 0x%08x\n",
+		atomic_inc_return(&apb->count),
+		addr);
+
+	/*
+	 * Print backtrace on each CPU. This might be pointless if the fault
+	 * has happened on the same CPU as the IRQ handler is executed or
+	 * the other core proceeded further execution despite the error.
+	 * But if it's not, by looking at the trace we would get straight to
+	 * the cause of the problem.
+	 */
+	trigger_all_cpu_backtrace();
+
+	regmap_update_bits(apb->regs, APB_EHB_ISR, APB_EHB_ISR_PENDING, 0);
+
+	return IRQ_HANDLED;
+}
+
+static void bt1_apb_clear_data(void *data)
+{
+	struct bt1_apb *apb = data;
+	struct platform_device *pdev = to_platform_device(apb->dev);
+
+	platform_set_drvdata(pdev, NULL);
+}
+
+static struct bt1_apb *bt1_apb_create_data(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	struct bt1_apb *apb;
+	int ret;
+
+	apb = devm_kzalloc(dev, sizeof(*apb), GFP_KERNEL);
+	if (!apb)
+		return ERR_PTR(-ENOMEM);
+
+	ret = devm_add_action(dev, bt1_apb_clear_data, apb);
+	if (ret) {
+		dev_err(dev, "Can't add APB EHB data clear action\n");
+		return ERR_PTR(ret);
+	}
+
+	apb->dev = dev;
+	atomic_set(&apb->count, 0);
+	platform_set_drvdata(pdev, apb);
+
+	return apb;
+}
+
+static int bt1_apb_request_regs(struct bt1_apb *apb)
+{
+	struct platform_device *pdev = to_platform_device(apb->dev);
+	void __iomem *regs;
+
+	regs = devm_platform_ioremap_resource_byname(pdev, "ehb");
+	if (IS_ERR(regs)) {
+		dev_err(apb->dev, "Couldn't map APB EHB registers\n");
+		return PTR_ERR(regs);
+	}
+
+	apb->regs = devm_regmap_init_mmio(apb->dev, regs, &bt1_apb_regmap_cfg);
+	if (IS_ERR(apb->regs)) {
+		dev_err(apb->dev, "Couldn't create APB EHB regmap\n");
+		return PTR_ERR(apb->regs);
+	}
+
+	apb->res = devm_platform_ioremap_resource_byname(pdev, "nodev");
+	if (IS_ERR(apb->res)) {
+		dev_err(apb->dev, "Couldn't map reserved region\n");
+		return PTR_ERR(apb->res);
+	}
+
+	return 0;
+}
+
+static int bt1_apb_request_rst(struct bt1_apb *apb)
+{
+	int ret;
+
+	apb->prst = devm_reset_control_get_optional_exclusive(apb->dev, "prst");
+	if (IS_ERR(apb->prst)) {
+		dev_warn(apb->dev, "Couldn't get reset control line\n");
+		return PTR_ERR(apb->prst);
+	}
+
+	ret = reset_control_deassert(apb->prst);
+	if (ret)
+		dev_err(apb->dev, "Failed to deassert the reset line\n");
+
+	return ret;
+}
+
+static void bt1_apb_disable_clk(void *data)
+{
+	struct bt1_apb *apb = data;
+
+	clk_disable_unprepare(apb->pclk);
+}
+
+static int bt1_apb_request_clk(struct bt1_apb *apb)
+{
+	int ret;
+
+	apb->pclk = devm_clk_get(apb->dev, "pclk");
+	if (IS_ERR(apb->pclk)) {
+		dev_err(apb->dev, "Couldn't get APB clock descriptor\n");
+		return PTR_ERR(apb->pclk);
+	}
+
+	ret = clk_prepare_enable(apb->pclk);
+	if (ret) {
+		dev_err(apb->dev, "Couldn't enable the APB clock\n");
+		return ret;
+	}
+
+	ret = devm_add_action_or_reset(apb->dev, bt1_apb_disable_clk, apb);
+	if (ret) {
+		dev_err(apb->dev, "Can't add APB EHB clocks disable action\n");
+		return ret;
+	}
+
+	apb->rate = clk_get_rate(apb->pclk);
+	if (!apb->rate) {
+		dev_err(apb->dev, "Invalid clock rate\n");
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+static void bt1_apb_clear_irq(void *data)
+{
+	struct bt1_apb *apb = data;
+
+	regmap_update_bits(apb->regs, APB_EHB_ISR, APB_EHB_ISR_MASK, 0);
+}
+
+static int bt1_apb_request_irq(struct bt1_apb *apb)
+{
+	struct platform_device *pdev = to_platform_device(apb->dev);
+	int ret;
+
+	apb->irq = platform_get_irq(pdev, 0);
+	if (apb->irq < 0)
+		return apb->irq;
+
+	ret = devm_request_irq(apb->dev, apb->irq, bt1_apb_isr, IRQF_SHARED,
+			       "bt1-apb", apb);
+	if (ret) {
+		dev_err(apb->dev, "Couldn't request APB EHB IRQ\n");
+		return ret;
+	}
+
+	ret = devm_add_action(apb->dev, bt1_apb_clear_irq, apb);
+	if (ret) {
+		dev_err(apb->dev, "Can't add APB EHB IRQs clear action\n");
+		return ret;
+	}
+
+	/* Unmask IRQ and clear it' pending flag. */
+	regmap_update_bits(apb->regs, APB_EHB_ISR,
+			   APB_EHB_ISR_PENDING | APB_EHB_ISR_MASK,
+			   APB_EHB_ISR_MASK);
+
+	return 0;
+}
+
+static ssize_t count_show(struct device *dev, struct device_attribute *attr,
+			  char *buf)
+{
+	struct bt1_apb *apb = dev_get_drvdata(dev);
+
+	return scnprintf(buf, PAGE_SIZE, "%d\n", atomic_read(&apb->count));
+}
+static DEVICE_ATTR_RO(count);
+
+static ssize_t timeout_show(struct device *dev, struct device_attribute *attr,
+			    char *buf)
+{
+	struct bt1_apb *apb = dev_get_drvdata(dev);
+	unsigned long timeout;
+	int ret;
+	u32 n;
+
+	ret = regmap_read(apb->regs, APB_EHB_TIMEOUT, &n);
+	if (ret)
+		return ret;
+
+	timeout = bt1_apb_n_to_timeout_us(apb, n);
+
+	return scnprintf(buf, PAGE_SIZE, "%lu\n", timeout);
+}
+
+static ssize_t timeout_store(struct device *dev,
+			     struct device_attribute *attr,
+			     const char *buf, size_t count)
+{
+	struct bt1_apb *apb = dev_get_drvdata(dev);
+	unsigned long timeout;
+	int ret;
+	u32 n;
+
+	if (kstrtoul(buf, 0, &timeout) < 0)
+		return -EINVAL;
+
+	n = bt1_apb_timeout_to_n_us(apb, timeout);
+	n = clamp(n, APB_EHB_TIMEOUT_MIN, APB_EHB_TIMEOUT_MAX);
+
+	ret = regmap_write(apb->regs, APB_EHB_TIMEOUT, n);
+
+	return ret ?: count;
+}
+static DEVICE_ATTR_RW(timeout);
+
+static int inject_error_show(struct device *dev, struct device_attribute *attr,
+			     char *buf)
+{
+	return scnprintf(buf, PAGE_SIZE, "Error injection: nodev irq\n");
+}
+
+static int inject_error_store(struct device *dev,
+			      struct device_attribute *attr,
+			      const char *data, size_t count)
+{
+	struct bt1_apb *apb = dev_get_drvdata(dev);
+
+	/*
+	 * Either dummy read from the unmapped address in the APB IO area
+	 * or manually set the IRQ status.
+	 */
+	if (!strncmp(data, "nodev", 5))
+		readl(apb->res);
+	else if (!strncmp(data, "irq", 3))
+		regmap_update_bits(apb->regs, APB_EHB_ISR, APB_EHB_ISR_PENDING,
+				   APB_EHB_ISR_PENDING);
+	else
+		return -EINVAL;
+
+	return count;
+}
+static DEVICE_ATTR_RW(inject_error);
+
+static struct attribute *bt1_apb_sysfs_attrs[] = {
+	&dev_attr_count.attr,
+	&dev_attr_timeout.attr,
+	&dev_attr_inject_error.attr,
+	NULL
+};
+ATTRIBUTE_GROUPS(bt1_apb_sysfs);
+
+static void bt1_apb_remove_sysfs(void *data)
+{
+	struct bt1_apb *apb = data;
+
+	device_remove_groups(apb->dev, bt1_apb_sysfs_groups);
+}
+
+static int bt1_apb_init_sysfs(struct bt1_apb *apb)
+{
+	int ret;
+
+	ret = device_add_groups(apb->dev, bt1_apb_sysfs_groups);
+	if (ret) {
+		dev_err(apb->dev, "Failed to create EHB APB sysfs nodes\n");
+		return ret;
+	}
+
+	ret = devm_add_action_or_reset(apb->dev, bt1_apb_remove_sysfs, apb);
+	if (ret)
+		dev_err(apb->dev, "Can't add APB EHB sysfs remove action\n");
+
+	return ret;
+}
+
+static int bt1_apb_probe(struct platform_device *pdev)
+{
+	struct bt1_apb *apb;
+	int ret;
+
+	apb = bt1_apb_create_data(pdev);
+	if (IS_ERR(apb))
+		return PTR_ERR(apb);
+
+	ret = bt1_apb_request_regs(apb);
+	if (ret)
+		return ret;
+
+	ret = bt1_apb_request_rst(apb);
+	if (ret)
+		return ret;
+
+	ret = bt1_apb_request_clk(apb);
+	if (ret)
+		return ret;
+
+	ret = bt1_apb_request_irq(apb);
+	if (ret)
+		return ret;
+
+	ret = bt1_apb_init_sysfs(apb);
+	if (ret)
+		return ret;
+
+	return 0;
+}
+
+static const struct of_device_id bt1_apb_of_match[] = {
+	{ .compatible = "baikal,bt1-apb" },
+	{ }
+};
+MODULE_DEVICE_TABLE(of, bt1_apb_of_match);
+
+static struct platform_driver bt1_apb_driver = {
+	.probe = bt1_apb_probe,
+	.driver = {
+		.name = "bt1-apb",
+		.of_match_table = bt1_apb_of_match
+	}
+};
+module_platform_driver(bt1_apb_driver);
+
+MODULE_AUTHOR("Serge Semin <Sergey.Semin@baikalelectronics.ru>");
+MODULE_DESCRIPTION("Baikal-T1 APB-bus driver");
+MODULE_LICENSE("GPL v2");
-- 
2.26.2