lib: Add register read/write tracing support

Generic MMIO read/write i.e., __raw_{read,write}{b,l,w,q} accessors
are typically used to read/write from/to memory mapped registers
and can cause hangs or some undefined behaviour in following few
cases,

* If the access to the register space is unclocked, for example: if
  there is an access to multimedia(MM) block registers without MM
  clocks.

* If the register space is protected and not set to be accessible from
  non-secure world, for example: only EL3 (EL: Exception level) access
  is allowed and any EL2/EL1 access is forbidden.

* If xPU(memory/register protection units) is controlling access to
  certain memory/register space for specific clients.

and more...

Such cases usually results in instant reboot/SErrors/NOC or interconnect
hangs and tracing these register accesses can be very helpful to debug
such issues during initial development stages and also in later stages.

So use ftrace trace events to log such MMIO register accesses which
provides rich feature set such as early enablement of trace events,
filtering capability, dumping ftrace logs on console and many more.

Sample output:

rwmmio_write: __qcom_geni_serial_console_write+0x160/0x1e0 width=32 val=0xa0d5d addr=0xfffffbfffdbff700
rwmmio_post_write: __qcom_geni_serial_console_write+0x160/0x1e0 width=32 val=0xa0d5d addr=0xfffffbfffdbff700
rwmmio_read: qcom_geni_serial_poll_bit+0x94/0x138 width=32 addr=0xfffffbfffdbff610
rwmmio_post_read: qcom_geni_serial_poll_bit+0x94/0x138 width=32 val=0x0 addr=0xfffffbfffdbff610

Co-developed-by: Sai Prakash Ranjan <[email protected]>
Signed-off-by: Prasad Sodagudi <[email protected]>
Signed-off-by: Sai Prakash Ranjan <[email protected]>
Acked-by: Steven Rostedt (Google) <[email protected]>
Signed-off-by: Arnd Bergmann <[email protected]>

arch/Kconfig

@@ -1396,6 +1396,9 @@ config ARCH_HAS_ELFCORE_COMPAT
 config ARCH_HAS_PARANOID_L1D_FLUSH
 	bool
 
+config ARCH_HAVE_TRACE_MMIO_ACCESS
+	bool
+
 config DYNAMIC_SIGFRAME
 	bool
 

arch/arm64/Kconfig

@@ -49,6 +49,7 @@ config ARM64
 	select ARCH_HAS_ZONE_DMA_SET if EXPERT
 	select ARCH_HAVE_ELF_PROT
 	select ARCH_HAVE_NMI_SAFE_CMPXCHG
+	select ARCH_HAVE_TRACE_MMIO_ACCESS
 	select ARCH_INLINE_READ_LOCK if !PREEMPTION
 	select ARCH_INLINE_READ_LOCK_BH if !PREEMPTION
 	select ARCH_INLINE_READ_LOCK_IRQ if !PREEMPTION

include/trace/events/rwmmio.h

@@ -0,0 +1,97 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (c) 2021-2022 Qualcomm Innovation Center, Inc. All rights reserved.
+ */
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM rwmmio
+
+#if !defined(_TRACE_RWMMIO_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_RWMMIO_H
+
+#include <linux/tracepoint.h>
+
+DECLARE_EVENT_CLASS(rwmmio_rw_template,
+
+	TP_PROTO(unsigned long caller, u64 val, u8 width, volatile void __iomem *addr),
+
+	TP_ARGS(caller, val, width, addr),
+
+	TP_STRUCT__entry(
+		__field(unsigned long, caller)
+		__field(unsigned long, addr)
+		__field(u64, val)
+		__field(u8, width)
+	),
+
+	TP_fast_assign(
+		__entry->caller = caller;
+		__entry->val = val;
+		__entry->addr = (unsigned long)addr;
+		__entry->width = width;
+	),
+
+	TP_printk("%pS width=%d val=%#llx addr=%#lx",
+		(void *)__entry->caller, __entry->width,
+		__entry->val, __entry->addr)
+);
+
+DEFINE_EVENT(rwmmio_rw_template, rwmmio_write,
+	TP_PROTO(unsigned long caller, u64 val, u8 width, volatile void __iomem *addr),
+	TP_ARGS(caller, val, width, addr)
+);
+
+DEFINE_EVENT(rwmmio_rw_template, rwmmio_post_write,
+	TP_PROTO(unsigned long caller, u64 val, u8 width, volatile void __iomem *addr),
+	TP_ARGS(caller, val, width, addr)
+);
+
+TRACE_EVENT(rwmmio_read,
+
+	TP_PROTO(unsigned long caller, u8 width, const volatile void __iomem *addr),
+
+	TP_ARGS(caller, width, addr),
+
+	TP_STRUCT__entry(
+		__field(unsigned long, caller)
+		__field(unsigned long, addr)
+		__field(u8, width)
+	),
+
+	TP_fast_assign(
+		__entry->caller = caller;
+		__entry->addr = (unsigned long)addr;
+		__entry->width = width;
+	),
+
+	TP_printk("%pS width=%d addr=%#lx",
+		 (void *)__entry->caller, __entry->width, __entry->addr)
+);
+
+TRACE_EVENT(rwmmio_post_read,
+
+	TP_PROTO(unsigned long caller, u64 val, u8 width, const volatile void __iomem *addr),
+
+	TP_ARGS(caller, val, width, addr),
+
+	TP_STRUCT__entry(
+		__field(unsigned long, caller)
+		__field(unsigned long, addr)
+		__field(u64, val)
+		__field(u8, width)
+	),
+
+	TP_fast_assign(
+		__entry->caller = caller;
+		__entry->val = val;
+		__entry->addr = (unsigned long)addr;
+		__entry->width = width;
+	),
+
+	TP_printk("%pS width=%d val=%#llx addr=%#lx",
+		 (void *)__entry->caller, __entry->width,
+		 __entry->val, __entry->addr)
+);
+
+#endif /* _TRACE_RWMMIO_H */
+
+#include <trace/define_trace.h>

lib/Kconfig

@@ -118,6 +118,13 @@ config INDIRECT_IOMEM_FALLBACK
 	  mmio accesses when the IO memory address is not a registered
 	  emulated region.
 
+config TRACE_MMIO_ACCESS
+	bool "Register read/write tracing"
+	depends on TRACING && ARCH_HAVE_TRACE_MMIO_ACCESS
+	help
+	  Create tracepoints for MMIO read/write operations. These trace events
+	  can be used for logging all MMIO read/write operations.
+
 source "lib/crypto/Kconfig"
 
 config CRC_CCITT

lib/Makefile

@@ -151,6 +151,8 @@ lib-y += logic_pio.o
 
 lib-$(CONFIG_INDIRECT_IOMEM) += logic_iomem.o
 
+obj-$(CONFIG_TRACE_MMIO_ACCESS) += trace_readwrite.o
+
 obj-$(CONFIG_GENERIC_HWEIGHT) += hweight.o
 
 obj-$(CONFIG_BTREE) += btree.o

lib/trace_readwrite.c

@@ -0,0 +1,47 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Register read and write tracepoints
+ *
+ * Copyright (c) 2021-2022 Qualcomm Innovation Center, Inc. All rights reserved.
+ */
+
+#include <linux/ftrace.h>
+#include <linux/module.h>
+#include <asm-generic/io.h>
+
+#define CREATE_TRACE_POINTS
+#include <trace/events/rwmmio.h>
+
+#ifdef CONFIG_TRACE_MMIO_ACCESS
+void log_write_mmio(u64 val, u8 width, volatile void __iomem *addr,
+		    unsigned long caller_addr)
+{
+	trace_rwmmio_write(caller_addr, val, width, addr);
+}
+EXPORT_SYMBOL_GPL(log_write_mmio);
+EXPORT_TRACEPOINT_SYMBOL_GPL(rwmmio_write);
+
+void log_post_write_mmio(u64 val, u8 width, volatile void __iomem *addr,
+			 unsigned long caller_addr)
+{
+	trace_rwmmio_post_write(caller_addr, val, width, addr);
+}
+EXPORT_SYMBOL_GPL(log_post_write_mmio);
+EXPORT_TRACEPOINT_SYMBOL_GPL(rwmmio_post_write);
+
+void log_read_mmio(u8 width, const volatile void __iomem *addr,
+		   unsigned long caller_addr)
+{
+	trace_rwmmio_read(caller_addr, width, addr);
+}
+EXPORT_SYMBOL_GPL(log_read_mmio);
+EXPORT_TRACEPOINT_SYMBOL_GPL(rwmmio_read);
+
+void log_post_read_mmio(u64 val, u8 width, const volatile void __iomem *addr,
+			unsigned long caller_addr)
+{
+	trace_rwmmio_post_read(caller_addr, val, width, addr);
+}
+EXPORT_SYMBOL_GPL(log_post_read_mmio);
+EXPORT_TRACEPOINT_SYMBOL_GPL(rwmmio_post_read);
+#endif /* CONFIG_TRACE_MMIO_ACCESS */