drivers/misc: add Aspeed LPC snoop driver

This driver enables the LPC snoop hardware on the ASPEED BMC
which generates an interrupt upon every write to an I/O port
by the host.

This is typically used to monitor BIOS boot progress by listening
to well-known debug port 80h.

The functionality in this commit just saves all snooped values
to a circular 2K buffer in the kernel, subsequent commits can
act on the values to do things with them.

Signed-off-by: Robert Lippert <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/misc/Kconfig

···
 	  ioctl()s, the driver also provides a read/write interface to a BMC ram
 	  region where the host LPC read/write region can be buffered.
 
+config ASPEED_LPC_SNOOP
+	tristate "Aspeed ast2500 HOST LPC snoop support"
+	depends on (ARCH_ASPEED || COMPILE_TEST) && REGMAP && MFD_SYSCON
+	help
+	  Provides a driver to control the LPC snoop interface which
+	  allows the BMC to listen on and save the data written by
+	  the host to an arbitrary LPC I/O port.
+
 config PCI_ENDPOINT_TEST
 	depends on PCI
 	select CRC32

drivers/misc/Makefile

···
 obj-$(CONFIG_VEXPRESS_SYSCFG)	+= vexpress-syscfg.o
 obj-$(CONFIG_CXL_BASE)		+= cxl/
 obj-$(CONFIG_ASPEED_LPC_CTRL)	+= aspeed-lpc-ctrl.o
+obj-$(CONFIG_ASPEED_LPC_SNOOP)	+= aspeed-lpc-snoop.o
 obj-$(CONFIG_PCI_ENDPOINT_TEST)	+= pci_endpoint_test.o
 
 lkdtm-$(CONFIG_LKDTM)		+= lkdtm_core.o

drivers/misc/aspeed-lpc-snoop.c

···
+/*
+ * Copyright 2017 Google Inc
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version
+ * 2 of the License, or (at your option) any later version.
+ *
+ * Provides a simple driver to control the ASPEED LPC snoop interface which
+ * allows the BMC to listen on and save the data written by
+ * the host to an arbitrary LPC I/O port.
+ *
+ * Typically used by the BMC to "watch" host boot progress via port
+ * 0x80 writes made by the BIOS during the boot process.
+ */
+
+#include <linux/bitops.h>
+#include <linux/interrupt.h>
+#include <linux/kfifo.h>
+#include <linux/mfd/syscon.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+#include <linux/regmap.h>
+
+#define DEVICE_NAME	"aspeed-lpc-snoop"
+
+#define NUM_SNOOP_CHANNELS 2
+#define SNOOP_FIFO_SIZE 2048
+
+#define HICR5	0x0
+#define HICR5_EN_SNP0W		BIT(0)
+#define HICR5_ENINT_SNP0W	BIT(1)
+#define HICR5_EN_SNP1W		BIT(2)
+#define HICR5_ENINT_SNP1W	BIT(3)
+
+#define HICR6	0x4
+#define HICR6_STR_SNP0W		BIT(0)
+#define HICR6_STR_SNP1W		BIT(1)
+#define SNPWADR	0x10
+#define SNPWADR_CH0_MASK	GENMASK(15, 0)
+#define SNPWADR_CH0_SHIFT	0
+#define SNPWADR_CH1_MASK	GENMASK(31, 16)
+#define SNPWADR_CH1_SHIFT	16
+#define SNPWDR	0x14
+#define SNPWDR_CH0_MASK		GENMASK(7, 0)
+#define SNPWDR_CH0_SHIFT	0
+#define SNPWDR_CH1_MASK		GENMASK(15, 8)
+#define SNPWDR_CH1_SHIFT	8
+#define HICRB	0x80
+#define HICRB_ENSNP0D		BIT(14)
+#define HICRB_ENSNP1D		BIT(15)
+
+struct aspeed_lpc_snoop {
+	struct regmap		*regmap;
+	int			irq;
+	struct kfifo		snoop_fifo[NUM_SNOOP_CHANNELS];
+};
+
+/* Save a byte to a FIFO and discard the oldest byte if FIFO is full */
+static void put_fifo_with_discard(struct kfifo *fifo, u8 val)
+{
+	if (!kfifo_initialized(fifo))
+		return;
+	if (kfifo_is_full(fifo))
+		kfifo_skip(fifo);
+	kfifo_put(fifo, val);
+}
+
+static irqreturn_t aspeed_lpc_snoop_irq(int irq, void *arg)
+{
+	struct aspeed_lpc_snoop *lpc_snoop = arg;
+	u32 reg, data;
+
+	if (regmap_read(lpc_snoop->regmap, HICR6, &reg))
+		return IRQ_NONE;
+
+	/* Check if one of the snoop channels is interrupting */
+	reg &= (HICR6_STR_SNP0W | HICR6_STR_SNP1W);
+	if (!reg)
+		return IRQ_NONE;
+
+	/* Ack pending IRQs */
+	regmap_write(lpc_snoop->regmap, HICR6, reg);
+
+	/* Read and save most recent snoop'ed data byte to FIFO */
+	regmap_read(lpc_snoop->regmap, SNPWDR, &data);
+
+	if (reg & HICR6_STR_SNP0W) {
+		u8 val = (data & SNPWDR_CH0_MASK) >> SNPWDR_CH0_SHIFT;
+
+		put_fifo_with_discard(&lpc_snoop->snoop_fifo[0], val);
+	}
+	if (reg & HICR6_STR_SNP1W) {
+		u8 val = (data & SNPWDR_CH1_MASK) >> SNPWDR_CH1_SHIFT;
+
+		put_fifo_with_discard(&lpc_snoop->snoop_fifo[1], val);
+	}
+
+	return IRQ_HANDLED;
+}
+
+static int aspeed_lpc_snoop_config_irq(struct aspeed_lpc_snoop *lpc_snoop,
+				       struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	int rc;
+
+	lpc_snoop->irq = platform_get_irq(pdev, 0);
+	if (!lpc_snoop->irq)
+		return -ENODEV;
+
+	rc = devm_request_irq(dev, lpc_snoop->irq,
+			      aspeed_lpc_snoop_irq, IRQF_SHARED,
+			      DEVICE_NAME, lpc_snoop);
+	if (rc < 0) {
+		dev_warn(dev, "Unable to request IRQ %d\n", lpc_snoop->irq);
+		lpc_snoop->irq = 0;
+		return rc;
+	}
+
+	return 0;
+}
+
+static int aspeed_lpc_enable_snoop(struct aspeed_lpc_snoop *lpc_snoop,
+				  int channel, u16 lpc_port)
+{
+	int rc = 0;
+	u32 hicr5_en, snpwadr_mask, snpwadr_shift, hicrb_en;
+
+	/* Create FIFO datastructure */
+	rc = kfifo_alloc(&lpc_snoop->snoop_fifo[channel],
+			 SNOOP_FIFO_SIZE, GFP_KERNEL);
+	if (rc)
+		return rc;
+
+	/* Enable LPC snoop channel at requested port */
+	switch (channel) {
+	case 0:
+		hicr5_en = HICR5_EN_SNP0W | HICR5_ENINT_SNP0W;
+		snpwadr_mask = SNPWADR_CH0_MASK;
+		snpwadr_shift = SNPWADR_CH0_SHIFT;
+		hicrb_en = HICRB_ENSNP0D;
+		break;
+	case 1:
+		hicr5_en = HICR5_EN_SNP1W | HICR5_ENINT_SNP1W;
+		snpwadr_mask = SNPWADR_CH1_MASK;
+		snpwadr_shift = SNPWADR_CH1_SHIFT;
+		hicrb_en = HICRB_ENSNP1D;
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	regmap_update_bits(lpc_snoop->regmap, HICR5, hicr5_en, hicr5_en);
+	regmap_update_bits(lpc_snoop->regmap, SNPWADR, snpwadr_mask,
+			   lpc_port << snpwadr_shift);
+	regmap_update_bits(lpc_snoop->regmap, HICRB, hicrb_en, hicrb_en);
+
+	return rc;
+}
+
+static void aspeed_lpc_disable_snoop(struct aspeed_lpc_snoop *lpc_snoop,
+				     int channel)
+{
+	switch (channel) {
+	case 0:
+		regmap_update_bits(lpc_snoop->regmap, HICR5,
+				   HICR5_EN_SNP0W | HICR5_ENINT_SNP0W,
+				   0);
+		break;
+	case 1:
+		regmap_update_bits(lpc_snoop->regmap, HICR5,
+				   HICR5_EN_SNP1W | HICR5_ENINT_SNP1W,
+				   0);
+		break;
+	default:
+		return;
+	}
+
+	kfifo_free(&lpc_snoop->snoop_fifo[channel]);
+}
+
+static int aspeed_lpc_snoop_probe(struct platform_device *pdev)
+{
+	struct aspeed_lpc_snoop *lpc_snoop;
+	struct device *dev;
+	u32 port;
+	int rc;
+
+	dev = &pdev->dev;
+
+	lpc_snoop = devm_kzalloc(dev, sizeof(*lpc_snoop), GFP_KERNEL);
+	if (!lpc_snoop)
+		return -ENOMEM;
+
+	lpc_snoop->regmap = syscon_node_to_regmap(
+			pdev->dev.parent->of_node);
+	if (IS_ERR(lpc_snoop->regmap)) {
+		dev_err(dev, "Couldn't get regmap\n");
+		return -ENODEV;
+	}
+
+	dev_set_drvdata(&pdev->dev, lpc_snoop);
+
+	rc = of_property_read_u32_index(dev->of_node, "snoop-ports", 0, &port);
+	if (rc) {
+		dev_err(dev, "no snoop ports configured\n");
+		return -ENODEV;
+	}
+
+	rc = aspeed_lpc_snoop_config_irq(lpc_snoop, pdev);
+	if (rc)
+		return rc;
+
+	rc = aspeed_lpc_enable_snoop(lpc_snoop, 0, port);
+	if (rc)
+		return rc;
+
+	/* Configuration of 2nd snoop channel port is optional */
+	if (of_property_read_u32_index(dev->of_node, "snoop-ports",
+				       1, &port) == 0) {
+		rc = aspeed_lpc_enable_snoop(lpc_snoop, 1, port);
+		if (rc)
+			aspeed_lpc_disable_snoop(lpc_snoop, 0);
+	}
+
+	return rc;
+}
+
+static int aspeed_lpc_snoop_remove(struct platform_device *pdev)
+{
+	struct aspeed_lpc_snoop *lpc_snoop = dev_get_drvdata(&pdev->dev);
+
+	/* Disable both snoop channels */
+	aspeed_lpc_disable_snoop(lpc_snoop, 0);
+	aspeed_lpc_disable_snoop(lpc_snoop, 1);
+
+	return 0;
+}
+
+static const struct of_device_id aspeed_lpc_snoop_match[] = {
+	{ .compatible = "aspeed,ast2500-lpc-snoop" },
+	{ },
+};
+
+static struct platform_driver aspeed_lpc_snoop_driver = {
+	.driver = {
+		.name		= DEVICE_NAME,
+		.of_match_table = aspeed_lpc_snoop_match,
+	},
+	.probe = aspeed_lpc_snoop_probe,
+	.remove = aspeed_lpc_snoop_remove,
+};
+
+module_platform_driver(aspeed_lpc_snoop_driver);
+
+MODULE_DEVICE_TABLE(of, aspeed_lpc_snoop_match);
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Robert Lippert <[e-mail]>");
+MODULE_DESCRIPTION("Linux driver to control Aspeed LPC snoop functionality");