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From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: Thu, 21 Sep 2023 16:15:13 +0200
Subject: [PATCH 2/5] drm/amd/display: Simplify the per-CPU usage.
Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/6.6/older/patches-6.6.7-rt18.tar.xz
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 <bigeasy@linutronix.de>
---
drivers/gpu/drm/amd/display/amdgpu_dm/dc_fpu.c | 50 ++++++++++---------------
1 file changed, 20 insertions(+), 30 deletions(-)
--- 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
*/
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_n
*/
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();
}
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