From 13345b6e1dccf7f0404111eb4081834eaf628563 Mon Sep 17 00:00:00 2001 From: Sebastian Andrzej Siewior Date: Thu, 21 Sep 2023 16:15:13 +0200 Subject: [PATCH 011/195] 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. Link: https://lore.kernel.org/r/20230921141516.520471-3-bigeasy@linutronix.de Signed-off-by: Sebastian Andrzej Siewior --- .../gpu/drm/amd/display/amdgpu_dm/dc_fpu.c | 50 ++++++++----------- 1 file changed, 20 insertions(+), 30 deletions(-) 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 86f4c0e04654..8bd5926b47e0 100644 --- 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(); } -- 2.43.0