drm/amd/display: Simplify the per-CPU usage.

The fpu_recursion_depth counter is used to ensure that dc_fpu_begin()
can be invoked multiple times while the FPU-disable function itself is
only invoked once. Also the counter part (dc_fpu_end()) is ballanced
properly.

Instead of using the get_cpu_ptr() dance around the inc it is simpler to
increment the per-CPU variable directly. Also the per-CPU variable has
to be incremented and decremented on the same CPU. This is ensured by
the inner-part which disables preemption. This is kind of not obvious,
works and the preempt-counter is touched a few times for no reason.

Disable preemption before incrementing fpu_recursion_depth for the first
time. Keep preemption disabled until dc_fpu_end() where the counter is
decremented making it obvious that the preemption has to stay disabled
while the counter is non-zero.
Use simple inc/dec functions.
Remove the nested preempt_disable/enable functions which are now not
needed.

Acked-by: Harry Wentland <harry.wentland@amd.com>
Reviewed-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Hamza Mahfooz <hamza.mahfooz@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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 86f4c0e..8bd5926 100644 (file)
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/dc_fpu.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/dc_fpu.c
@@ -60,11 +60,9 @@ static DEFINE_PER_CPU(int, fpu_recursion_depth);
  */
 inline void dc_assert_fp_enabled(void)
 {
-       int *pcpu, depth = 0;
+       int depth;
 
-       pcpu = get_cpu_ptr(&fpu_recursion_depth);
-       depth = *pcpu;
-       put_cpu_ptr(&fpu_recursion_depth);
+       depth = __this_cpu_read(fpu_recursion_depth);
 
        ASSERT(depth >= 1);
 }
@@ -84,32 +82,27 @@ inline void dc_assert_fp_enabled(void)
  */
 void dc_fpu_begin(const char *function_name, const int line)
 {
-       int *pcpu;
+       int depth;
 
-       pcpu = get_cpu_ptr(&fpu_recursion_depth);
-       *pcpu += 1;
+       preempt_disable();
+       depth = __this_cpu_inc_return(fpu_recursion_depth);
 
-       if (*pcpu == 1) {
+       if (depth == 1) {
 #if defined(CONFIG_X86) || defined(CONFIG_LOONGARCH)
                kernel_fpu_begin();
 #elif defined(CONFIG_PPC64)
-               if (cpu_has_feature(CPU_FTR_VSX_COMP)) {
-                       preempt_disable();
+               if (cpu_has_feature(CPU_FTR_VSX_COMP))
                        enable_kernel_vsx();
-               } else if (cpu_has_feature(CPU_FTR_ALTIVEC_COMP)) {
-                       preempt_disable();
+               else if (cpu_has_feature(CPU_FTR_ALTIVEC_COMP))
                        enable_kernel_altivec();
-               } else if (!cpu_has_feature(CPU_FTR_FPU_UNAVAILABLE)) {
-                       preempt_disable();
+               else if (!cpu_has_feature(CPU_FTR_FPU_UNAVAILABLE))
                        enable_kernel_fp();
-               }
 #elif defined(CONFIG_ARM64)
                kernel_neon_begin();
 #endif
        }
 
-       TRACE_DCN_FPU(true, function_name, line, *pcpu);
-       put_cpu_ptr(&fpu_recursion_depth);
+       TRACE_DCN_FPU(true, function_name, line, depth);
 }
 
 /**
@@ -124,29 +117,26 @@ void dc_fpu_begin(const char *function_name, const int line)
  */
 void dc_fpu_end(const char *function_name, const int line)
 {
-       int *pcpu;
+       int depth;
 
-       pcpu = get_cpu_ptr(&fpu_recursion_depth);
-       *pcpu -= 1;
-       if (*pcpu <= 0) {
+       depth = __this_cpu_dec_return(fpu_recursion_depth);
+       if (depth == 0) {
 #if defined(CONFIG_X86) || defined(CONFIG_LOONGARCH)
                kernel_fpu_end();
 #elif defined(CONFIG_PPC64)
-               if (cpu_has_feature(CPU_FTR_VSX_COMP)) {
+               if (cpu_has_feature(CPU_FTR_VSX_COMP))
                        disable_kernel_vsx();
-                       preempt_enable();
-               } else if (cpu_has_feature(CPU_FTR_ALTIVEC_COMP)) {
+               else if (cpu_has_feature(CPU_FTR_ALTIVEC_COMP))
                        disable_kernel_altivec();
-                       preempt_enable();
-               } else if (!cpu_has_feature(CPU_FTR_FPU_UNAVAILABLE)) {
+               else if (!cpu_has_feature(CPU_FTR_FPU_UNAVAILABLE))
                        disable_kernel_fp();
-                       preempt_enable();
-               }
 #elif defined(CONFIG_ARM64)
                kernel_neon_end();
 #endif
+       } else {
+               WARN_ON_ONCE(depth < 0);
        }
 
-       TRACE_DCN_FPU(false, function_name, line, *pcpu);
-       put_cpu_ptr(&fpu_recursion_depth);
+       TRACE_DCN_FPU(false, function_name, line, depth);
+       preempt_enable();
 }