drm/amd/display: Add control mechanism for FPU utilization

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 V3:
- Rebase

Change since V2:
- Christian: Do not use this_cpu_* between get/put_cpu_ptr().

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

Cc: Harry Wentland <harry.wentland@amd.com>
Cc: Anson Jacob <Anson.Jacob@amd.com>
Cc: Christian König <christian.koenig@amd.com>
Cc: Hersen Wu <hersenxs.wu@amd.com>
Cc: Aric Cyr <aric.cyr@amd.com>
Cc: Jun Lei <jun.lei@amd.com>
Cc: Dmytro Laktyushkin <dmytro.laktyushkin@amd.com>
Cc: Qingqing Zhuo <qingqing.zhuo@amd.com>
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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 230bb12..fdcaea2 100644 (file)
--- 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 d4ab27b..33807d7 100644 (file)
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/dc_fpu.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/dc_fpu.c
@@ -34,6 +34,19 @@
 #endif
 
 /**
+ * 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
  *   (usually __func__)
@@ -48,22 +61,30 @@
  */
 void dc_fpu_begin(const char *function_name, const int line)
 {
-       TRACE_DCN_FPU(true, function_name, line);
+       int *pcpu;
+
+       pcpu = get_cpu_ptr(&fpu_recursion_depth);
+       *pcpu += 1;
 
+       if (*pcpu == 1) {
 #if defined(CONFIG_X86)
-       kernel_fpu_begin();
+               kernel_fpu_begin();
 #elif defined(CONFIG_PPC64)
-       if (cpu_has_feature(CPU_FTR_VSX_COMP)) {
-               preempt_disable();
-               enable_kernel_vsx();
-       } else if (cpu_has_feature(CPU_FTR_ALTIVEC_COMP)) {
-               preempt_disable();
-               enable_kernel_altivec();
-       } else if (!cpu_has_feature(CPU_FTR_FPU_UNAVAILABLE)) {
-               preempt_disable();
-               enable_kernel_fp();
-       }
+               if (cpu_has_feature(CPU_FTR_VSX_COMP)) {
+                       preempt_disable();
+                       enable_kernel_vsx();
+               } else if (cpu_has_feature(CPU_FTR_ALTIVEC_COMP)) {
+                       preempt_disable();
+                       enable_kernel_altivec();
+               } else if (!cpu_has_feature(CPU_FTR_FPU_UNAVAILABLE)) {
+                       preempt_disable();
+                       enable_kernel_fp();
+               }
 #endif
+       }
+
+       TRACE_DCN_FPU(true, function_name, line, *pcpu);
+       put_cpu_ptr(&fpu_recursion_depth);
 }
 
 /**
@@ -78,19 +99,27 @@ 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);
+       int *pcpu;
+
+       pcpu = get_cpu_ptr(&fpu_recursion_depth);
+       *pcpu -= 1;
+       if (*pcpu <= 0) {
 #if defined(CONFIG_X86)
-       kernel_fpu_end();
+               kernel_fpu_end();
 #elif defined(CONFIG_PPC64)
-       if (cpu_has_feature(CPU_FTR_VSX_COMP)) {
-               disable_kernel_vsx();
-               preempt_enable();
-       } else if (cpu_has_feature(CPU_FTR_ALTIVEC_COMP)) {
-               disable_kernel_altivec();
-               preempt_enable();
-       } else if (!cpu_has_feature(CPU_FTR_FPU_UNAVAILABLE)) {
-               disable_kernel_fp();
-               preempt_enable();
-       }
+               if (cpu_has_feature(CPU_FTR_VSX_COMP)) {
+                       disable_kernel_vsx();
+                       preempt_enable();
+               } else if (cpu_has_feature(CPU_FTR_ALTIVEC_COMP)) {
+                       disable_kernel_altivec();
+                       preempt_enable();
+               } else if (!cpu_has_feature(CPU_FTR_FPU_UNAVAILABLE)) {
+                       disable_kernel_fp();
+                       preempt_enable();
+               }
 #endif
+       }
+
+       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 d598ba6..c711797 100644 (file)
--- 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)