powerpc/pseries: Export hardware trace macro dump via debugfs

This patch adds debugfs interface to export Hardware Trace Macro (HTM)
function data in a LPAR. New hypervisor call "H_HTM" has been
defined to setup, configure, control and dump the HTM data.
This patch supports only dumping of HTM data in a LPAR.
New debugfs folder called "htmdump" has been added under
/sys/kernel/debug/arch path which contains files need to
pass required parameters for the H_HTM dump function. New Kconfig
option called "CONFIG_HTMDUMP" is added in platform/pseries
for the same.

With this module loaded, list of files in debugfs path

/sys/kernel/debug/powerpc/htmdump
coreindexonchip  htmtype  nodalchipindex  nodeindex  trace

Signed-off-by: Abhishek Dubey <adubey@linux.ibm.com>
Co-developed-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Reviewed-by: Athira Rajeev <atrajeev@linux.vnet.ibm.com>
Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Link: https://patch.msgid.link/20250113164039.302017-2-adubey@linux.ibm.com

arch/powerpc/platforms/pseries/Kconfig

@@ -128,6 +128,15 @@ config CMM
 	  will be reused for other LPARs. The interface allows firmware to
 	  balance memory across many LPARs.
 
+config HTMDUMP
+	tristate "PowerVM data dumper"
+	depends on PPC_PSERIES && DEBUG_FS
+	default m
+	help
+	  Select this option, if you want to enable the kernel debugfs
+	  interface to dump the Hardware Trace Macro (HTM) function data
+	  in the LPAR.
+
 config HV_PERF_CTRS
 	bool "Hypervisor supplied PMU events (24x7 & GPCI)"
 	default y

arch/powerpc/platforms/pseries/Makefile

@@ -19,6 +19,7 @@ obj-$(CONFIG_HVC_CONSOLE)	+= hvconsole.o
 obj-$(CONFIG_HVCS)		+= hvcserver.o
 obj-$(CONFIG_HCALL_STATS)	+= hvCall_inst.o
 obj-$(CONFIG_CMM)		+= cmm.o
+obj-$(CONFIG_HTMDUMP)		+= htmdump.o
 obj-$(CONFIG_IO_EVENT_IRQ)	+= io_event_irq.o
 obj-$(CONFIG_LPARCFG)		+= lparcfg.o
 obj-$(CONFIG_IBMVIO)		+= vio.o

arch/powerpc/platforms/pseries/htmdump.c

@@ -0,0 +1,121 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (C) IBM Corporation, 2024
+ */
+
+#define pr_fmt(fmt) "htmdump: " fmt
+
+#include <linux/debugfs.h>
+#include <linux/module.h>
+#include <asm/io.h>
+#include <asm/machdep.h>
+#include <asm/plpar_wrappers.h>
+
+static void *htm_buf;
+static u32 nodeindex;
+static u32 nodalchipindex;
+static u32 coreindexonchip;
+static u32 htmtype;
+static struct dentry *htmdump_debugfs_dir;
+
+static ssize_t htmdump_read(struct file *filp, char __user *ubuf,
+			     size_t count, loff_t *ppos)
+{
+	void *htm_buf = filp->private_data;
+	unsigned long page, read_size, available;
+	loff_t offset;
+	long rc;
+
+	page = ALIGN_DOWN(*ppos, PAGE_SIZE);
+	offset = (*ppos) % PAGE_SIZE;
+
+	rc = htm_get_dump_hardware(nodeindex, nodalchipindex, coreindexonchip,
+				   htmtype, virt_to_phys(htm_buf), PAGE_SIZE, page);
+
+	switch (rc) {
+	case H_SUCCESS:
+	/* H_PARTIAL for the case where all available data can't be
+	 * returned due to buffer size constraint.
+	 */
+	case H_PARTIAL:
+		break;
+	/* H_NOT_AVAILABLE indicates reading from an offset outside the range,
+	 * i.e. past end of file.
+	 */
+	case H_NOT_AVAILABLE:
+		return 0;
+	case H_BUSY:
+	case H_LONG_BUSY_ORDER_1_MSEC:
+	case H_LONG_BUSY_ORDER_10_MSEC:
+	case H_LONG_BUSY_ORDER_100_MSEC:
+	case H_LONG_BUSY_ORDER_1_SEC:
+	case H_LONG_BUSY_ORDER_10_SEC:
+	case H_LONG_BUSY_ORDER_100_SEC:
+		return -EBUSY;
+	case H_PARAMETER:
+	case H_P2:
+	case H_P3:
+	case H_P4:
+	case H_P5:
+	case H_P6:
+		return -EINVAL;
+	case H_STATE:
+		return -EIO;
+	case H_AUTHORITY:
+		return -EPERM;
+	}
+
+	available = PAGE_SIZE;
+	read_size = min(count, available);
+	*ppos += read_size;
+	return simple_read_from_buffer(ubuf, count, &offset, htm_buf, available);
+}
+
+static const struct file_operations htmdump_fops = {
+	.llseek = NULL,
+	.read	= htmdump_read,
+	.open	= simple_open,
+};
+
+static int htmdump_init_debugfs(void)
+{
+	htm_buf = kmalloc(PAGE_SIZE, GFP_KERNEL);
+	if (!htm_buf) {
+		pr_err("Failed to allocate htmdump buf\n");
+		return -ENOMEM;
+	}
+
+	htmdump_debugfs_dir = debugfs_create_dir("htmdump",
+						  arch_debugfs_dir);
+
+	debugfs_create_u32("nodeindex", 0600,
+			htmdump_debugfs_dir, &nodeindex);
+	debugfs_create_u32("nodalchipindex", 0600,
+			htmdump_debugfs_dir, &nodalchipindex);
+	debugfs_create_u32("coreindexonchip", 0600,
+			htmdump_debugfs_dir, &coreindexonchip);
+	debugfs_create_u32("htmtype", 0600,
+			htmdump_debugfs_dir, &htmtype);
+	debugfs_create_file("trace", 0400, htmdump_debugfs_dir, htm_buf, &htmdump_fops);
+
+	return 0;
+}
+
+static int __init htmdump_init(void)
+{
+	if (htmdump_init_debugfs())
+		return -ENOMEM;
+
+	return 0;
+}
+
+static void __exit htmdump_exit(void)
+{
+	debugfs_remove_recursive(htmdump_debugfs_dir);
+	kfree(htm_buf);
+}
+
+module_init(htmdump_init);
+module_exit(htmdump_exit);
+MODULE_DESCRIPTION("PHYP Hardware Trace Macro (HTM) data dumper");
+MODULE_LICENSE("GPL");