[PATCH v2 3/4] drm/amd/display: Add control mechanism for FPU utilization

[Rodrigo Siqueira]

DC invokes DC_FPU_START/END in multiple parts of the code; this can
create a situation where we invoke this FPU operation in a nested way or
exit too early. For avoiding this situation, this commit adds a
mechanism where dc_fpu_begin/end manages the access to
kernel_fpu_begin/end.

Change since V1:
- Use a better variable names
- Use get_cpu_ptr and put_cpu_ptr to better balance preemption enable
and disable

Signed-off-by: Rodrigo Siqueira <Rodrigo.Siqueira at amd.com>
---
 .../amd/display/amdgpu_dm/amdgpu_dm_trace.h   | 13 ++++---
 .../gpu/drm/amd/display/amdgpu_dm/dc_fpu.c    | 36 ++++++++++++++++---
 drivers/gpu/drm/amd/display/dc/dc_trace.h     |  4 +--
 3 files changed, 42 insertions(+), 11 deletions(-)

diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_trace.h b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_trace.h
index 230bb12c405e..fdcaea22b456 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_trace.h
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_trace.h
@@ -638,23 +638,26 @@ TRACE_EVENT(amdgpu_refresh_rate_track,
 );
 
 TRACE_EVENT(dcn_fpu,
-	    TP_PROTO(bool begin, const char *function, const int line),
-	    TP_ARGS(begin, function, line),
+	    TP_PROTO(bool begin, const char *function, const int line, const int recursion_depth),
+	    TP_ARGS(begin, function, line, recursion_depth),
 
 	    TP_STRUCT__entry(
 			     __field(bool, begin)
 			     __field(const char *, function)
 			     __field(int, line)
+			     __field(int, recursion_depth)
 	    ),
 	    TP_fast_assign(
 			   __entry->begin = begin;
 			   __entry->function = function;
 			   __entry->line = line;
+			   __entry->recursion_depth = recursion_depth;
 	    ),
-	    TP_printk("%s()+%d: %s",
+	    TP_printk("%s: recursion_depth: %d: %s()+%d:",
+		      __entry->begin ? "begin" : "end",
+		      __entry->recursion_depth,
 		      __entry->function,
-		      __entry->line,
-		      __entry->begin ? "begin" : "end"
+		      __entry->line
 	    )
 );
 
diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/dc_fpu.c b/drivers/gpu/drm/amd/display/amdgpu_dm/dc_fpu.c
index d5d156a4517e..73179e9e859a 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/dc_fpu.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/dc_fpu.c
@@ -28,6 +28,19 @@
 
 #include <asm/fpu/api.h>
 
+/**
+ * DOC: DC FPU manipulation overview
+ *
+ * DC core uses FPU operations in multiple parts of the code, which requires a
+ * more specialized way to manage these areas' entrance. To fulfill this
+ * requirement, we created some wrapper functions that encapsulate
+ * kernel_fpu_begin/end to better fit our need in the display component. In
+ * summary, in this file, you can find functions related to FPU operation
+ * management.
+ */
+
+static DEFINE_PER_CPU(int, fpu_recursion_depth);
+
 /**
  * dc_fpu_begin - Enables FPU protection
  * @function_name: A string containing the function name for debug purposes
@@ -43,8 +56,16 @@
  */
 void dc_fpu_begin(const char *function_name, const int line)
 {
-	TRACE_DCN_FPU(true, function_name, line);
-	kernel_fpu_begin();
+	int *pcpu;
+
+	pcpu = get_cpu_ptr(&fpu_recursion_depth);
+	*pcpu = this_cpu_inc_return(fpu_recursion_depth);
+
+	if (*pcpu == 1)
+		kernel_fpu_begin();
+
+	TRACE_DCN_FPU(true, function_name, line, *pcpu);
+	put_cpu_ptr(&fpu_recursion_depth);
 }
 
 /**
@@ -59,6 +80,13 @@ void dc_fpu_begin(const char *function_name, const int line)
  */
 void dc_fpu_end(const char *function_name, const int line)
 {
-	TRACE_DCN_FPU(false, function_name, line);
-	kernel_fpu_end();
+	int *pcpu;
+
+	pcpu = get_cpu_ptr(&fpu_recursion_depth);
+	*pcpu = this_cpu_dec_return(fpu_recursion_depth);
+	if (*pcpu <= 0)
+		kernel_fpu_end();
+
+	TRACE_DCN_FPU(false, function_name, line, *pcpu);
+	put_cpu_ptr(&fpu_recursion_depth);
 }
diff --git a/drivers/gpu/drm/amd/display/dc/dc_trace.h b/drivers/gpu/drm/amd/display/dc/dc_trace.h
index d598ba697e45..c711797e5c9e 100644
--- a/drivers/gpu/drm/amd/display/dc/dc_trace.h
+++ b/drivers/gpu/drm/amd/display/dc/dc_trace.h
@@ -38,5 +38,5 @@
 #define TRACE_DCN_CLOCK_STATE(dcn_clocks) \
 	trace_amdgpu_dm_dc_clocks_state(dcn_clocks)
 
-#define TRACE_DCN_FPU(begin, function, line) \
-	trace_dcn_fpu(begin, function, line)
+#define TRACE_DCN_FPU(begin, function, line, ref_count) \
+	trace_dcn_fpu(begin, function, line, ref_count)
-- 
2.25.1