Merge patch series "Add 'trace wipe'"

Jerome Forissier <jerome.forissier@linaro.org> says:

This short series adds the 'trace wipe' command which clears the trace
buffer, allowing to re-start a capture from scratch.

Link: https://lore.kernel.org/r/cover.1734093566.git.jerome.forissier@linaro.org

cmd/trace.c

@@ -100,6 +100,10 @@ int do_trace(struct cmd_tbl *cmdtp, int flag, int argc, char *const argv[])
 	case 's':
 		trace_print_stats();
 		break;
+	case 'w':
+		if (trace_wipe())
+			return CMD_RET_FAILURE;
+		break;
 	default:
 		return CMD_RET_USAGE;
 	}
@@ -113,6 +117,7 @@ U_BOOT_CMD(
 	"stats                        - display tracing statistics\n"
 	"trace pause                        - pause tracing\n"
 	"trace resume                       - resume tracing\n"
+	"trace wipe                         - wipe traces\n"
 	"trace funclist [<addr> <size>]     - dump function list into buffer\n"
 	"trace calls  [<addr> <size>]       "
 		"- dump function call trace into buffer"

doc/develop/trace.rst

@@ -163,6 +163,17 @@ you will see the time taken by each function shown against its exit record.
               u-boot-1     [000]     3.116466: funcgraph_entry:        0.063 us   |        memset();
               u-boot-1     [000]     3.116539: funcgraph_exit:         0.143 us   |        }
 
+The `trace wipe` command may be used to clear the trace buffer. It leaves
+tracing in its current enable state. This command is convenient when tracing a
+single command, for example:
+
+.. code-block:: console
+
+   => trace pause; trace wipe
+   => trace resume; dhcp; trace pause
+   => trace stats
+   ...
+
 Flame graph
 -----------
 

include/trace.h

@@ -100,6 +100,8 @@ void trace_set_enabled(int enabled);
 
 int trace_early_init(void);
 
+int trace_wipe(void);
+
 /**
  * Init the trace system
  *

lib/trace.c

@@ -351,14 +351,8 @@ static int get_func_count(void)
 	return gd->mon_len / FUNC_SITE_SIZE;
 }
 
-/**
- * trace_init() - initialize the tracing system and enable it
- *
- * @buff:	Pointer to trace buffer
- * @buff_size:	Size of trace buffer
- * Return:	0 if ok
- */
-int notrace trace_init(void *buff, size_t buff_size)
+static int notrace trace_init_(void *buff, size_t buff_size, bool copy_early,
+			       bool enable)
 {
 	int func_count = get_func_count();
 	size_t needed;
@@ -368,7 +362,7 @@ int notrace trace_init(void *buff, size_t buff_size)
 		return func_count;
 	trace_save_gd();
 
-	if (!was_disabled) {
+	if (copy_early) {
 #ifdef CONFIG_TRACE_EARLY
 		ulong used, count;
 		char *end;
@@ -394,9 +388,6 @@ int notrace trace_init(void *buff, size_t buff_size)
 		}
 		puts("\n");
 		memcpy(buff, hdr, used);
-#else
-		puts("trace: already enabled\n");
-		return -EALREADY;
 #endif
 	}
 	hdr = (struct trace_hdr *)buff;
@@ -419,13 +410,41 @@ int notrace trace_init(void *buff, size_t buff_size)
 	hdr->ftrace_size = (buff_size - needed) / sizeof(*hdr->ftrace);
 	hdr->depth_limit = CONFIG_TRACE_CALL_DEPTH_LIMIT;
 
-	puts("trace: enabled\n");
-	trace_enabled = 1;
+	printf("trace: initialized, %senabled\n", enable ? "" : "not ");
+	trace_enabled = enable;
 	trace_inited = 1;
 
 	return 0;
 }
 
+/**
+ * trace_init() - initialize the tracing system and enable it
+ *
+ * @buff:	Pointer to trace buffer
+ * @buff_size:	Size of trace buffer
+ * Return:	0 if ok
+ */
+int notrace trace_init(void *buff, size_t buff_size)
+{
+	/* If traces are enabled already, we may have early traces to copy */
+	return trace_init_(buff, buff_size, trace_enabled, true);
+}
+
+/**
+ * trace_wipe() - clear accumulated traced data
+ *
+ * May be called with tracing enabled or disabled.
+ */
+int notrace trace_wipe(void)
+{
+	bool was_enabled = trace_enabled;
+
+	if (trace_enabled)
+		trace_enabled = 0;
+	return trace_init_(gd->trace_buff, CONFIG_TRACE_BUFFER_SIZE,
+			   false, was_enabled);
+}
+
 #ifdef CONFIG_TRACE_EARLY
 /**
  * trace_early_init() - initialize the tracing system for early tracing

test/py/tests/test_trace.py

@@ -70,6 +70,32 @@ def collect_trace(cons):
     return fname, int(dm_f_time[0])
 
 
+def wipe_and_collect_trace(cons):
+    """Pause and wipe traces, return the number of calls (should be zero)
+
+    Args:
+        cons (ConsoleBase): U-Boot console
+
+    Returns:
+        int: the number of traced function calls reported by 'trace stats'
+    """
+    cons.run_command('trace pause')
+    cons.run_command('trace wipe')
+    out = cons.run_command('trace stats')
+
+    # The output is something like this:
+    # 117,221 function sites
+    #       0 function calls
+    #       0 untracked function calls
+    #       0 traced function calls
+
+    # Get a dict of values from the output
+    lines = [line.split(maxsplit=1) for line in out.splitlines() if line]
+    vals = {key: val.replace(',', '') for val, key in lines}
+
+    return int(vals['traced function calls'])
+
+
 def check_function(cons, fname, proftool, map_fname, trace_dat):
     """Check that the 'function' output works
 
@@ -304,3 +330,7 @@ def test_trace(u_boot_console):
     # This allows for CI being slow to run
     diff = abs(fg_time - dm_f_time)
     assert diff / dm_f_time < 0.3
+
+    # Check that the trace buffer can be wiped
+    numcalls = wipe_and_collect_trace(cons)
+    assert numcalls == 0