[RFC 0/2] Add generic FPU api similar to x86

[RFC 0/2] Add generic FPU api similar to x86

[Anson Jacob]

This is an attempt to have generic FPU enable/disable
calls similar to x86. 
So that we can simplify gpu/drm/amd/display/dc/os_types.h

Also adds FPU correctness logic seen in x86.

Anson Jacob (2):
  ppc/fpu: Add generic FPU api similar to x86
  drm/amd/display: Use PPC FPU functions

 arch/powerpc/include/asm/switch_to.h      |  29 ++---
 arch/powerpc/kernel/process.c             | 130 ++++++++++++++++++++++
 drivers/gpu/drm/amd/display/dc/os_types.h |  28 +----
 3 files changed, 139 insertions(+), 48 deletions(-)

-- 
2.25.1

[RFC 1/2] ppc/fpu: Add generic FPU api similar to x86

[Anson Jacob]

- Add kernel_fpu_begin & kernel_fpu_end API as x86
- Add logic similar to x86 to ensure fpu
  begin/end call correctness
- Add kernel_fpu_enabled to know if FPU is enabled

Signed-off-by: Anson Jacob <Anson.Jacob@amd.com>
---
 arch/powerpc/include/asm/switch_to.h |  29 ++----
 arch/powerpc/kernel/process.c        | 130 +++++++++++++++++++++++++++
 2 files changed, 137 insertions(+), 22 deletions(-)

diff --git a/arch/powerpc/include/asm/switch_to.h b/arch/powerpc/include/asm/switch_to.h
index 9d1fbd8be1c7..aded7aa661c0 100644
--- a/arch/powerpc/include/asm/switch_to.h
+++ b/arch/powerpc/include/asm/switch_to.h
@@ -41,10 +41,7 @@ extern void enable_kernel_fp(void);
 extern void flush_fp_to_thread(struct task_struct *);
 extern void giveup_fpu(struct task_struct *);
 extern void save_fpu(struct task_struct *);
-static inline void disable_kernel_fp(void)
-{
-	msr_check_and_clear(MSR_FP);
-}
+extern void disable_kernel_fp(void);
 #else
 static inline void save_fpu(struct task_struct *t) { }
 static inline void flush_fp_to_thread(struct task_struct *t) { }
@@ -55,10 +52,7 @@ extern void enable_kernel_altivec(void);
 extern void flush_altivec_to_thread(struct task_struct *);
 extern void giveup_altivec(struct task_struct *);
 extern void save_altivec(struct task_struct *);
-static inline void disable_kernel_altivec(void)
-{
-	msr_check_and_clear(MSR_VEC);
-}
+extern void disable_kernel_altivec(void);
 #else
 static inline void save_altivec(struct task_struct *t) { }
 static inline void __giveup_altivec(struct task_struct *t) { }
@@ -67,20 +61,7 @@ static inline void __giveup_altivec(struct task_struct *t) { }
 #ifdef CONFIG_VSX
 extern void enable_kernel_vsx(void);
 extern void flush_vsx_to_thread(struct task_struct *);
-static inline void disable_kernel_vsx(void)
-{
-	msr_check_and_clear(MSR_FP|MSR_VEC|MSR_VSX);
-}
-#else
-static inline void enable_kernel_vsx(void)
-{
-	BUILD_BUG();
-}
-
-static inline void disable_kernel_vsx(void)
-{
-	BUILD_BUG();
-}
+extern void disable_kernel_vsx(void);
 #endif
 
 #ifdef CONFIG_SPE
@@ -114,4 +95,8 @@ static inline void clear_task_ebb(struct task_struct *t)
 
 extern int set_thread_tidr(struct task_struct *t);
 
+bool kernel_fpu_enabled(void);
+void kernel_fpu_begin(void);
+void kernel_fpu_end(void);
+
 #endif /* _ASM_POWERPC_SWITCH_TO_H */
diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index 185beb290580..2ced8c6a3fab 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -75,6 +75,17 @@
 #define TM_DEBUG(x...) do { } while(0)
 #endif
 
+/*
+ * Track whether the kernel is using the FPU state
+ * currently.
+ *
+ * This flag is used:
+ *
+ *   - kernel_fpu_begin()/end() correctness
+ *   - kernel_fpu_enabled info
+ */
+static DEFINE_PER_CPU(bool, in_kernel_fpu);
+
 extern unsigned long _get_SP(void);
 
 #ifdef CONFIG_PPC_TRANSACTIONAL_MEM
@@ -212,6 +223,9 @@ void enable_kernel_fp(void)
 	unsigned long cpumsr;
 
 	WARN_ON(preemptible());
+	WARN_ON_ONCE(this_cpu_read(in_kernel_fpu));
+
+	this_cpu_write(in_kernel_fpu, true);
 
 	cpumsr = msr_check_and_set(MSR_FP);
 
@@ -231,6 +245,15 @@ void enable_kernel_fp(void)
 	}
 }
 EXPORT_SYMBOL(enable_kernel_fp);
+
+void disable_kernel_fp(void)
+{
+	WARN_ON_ONCE(!this_cpu_read(in_kernel_fpu));
+
+	this_cpu_write(in_kernel_fpu, false);
+	msr_check_and_clear(MSR_FP);
+}
+EXPORT_SYMBOL(disable_kernel_fp);
 #else
 static inline void __giveup_fpu(struct task_struct *tsk) { }
 #endif /* CONFIG_PPC_FPU */
@@ -263,6 +286,9 @@ void enable_kernel_altivec(void)
 	unsigned long cpumsr;
 
 	WARN_ON(preemptible());
+	WARN_ON_ONCE(this_cpu_read(in_kernel_fpu));
+
+	this_cpu_write(in_kernel_fpu, true);
 
 	cpumsr = msr_check_and_set(MSR_VEC);
 
@@ -283,6 +309,14 @@ void enable_kernel_altivec(void)
 }
 EXPORT_SYMBOL(enable_kernel_altivec);
 
+void disable_kernel_altivec(void)
+{
+	WARN_ON_ONCE(!this_cpu_read(in_kernel_fpu));
+
+	this_cpu_write(in_kernel_fpu, false);
+	msr_check_and_clear(MSR_VEC);
+}
+EXPORT_SYMBOL(disable_kernel_altivec);
 /*
  * Make sure the VMX/Altivec register state in the
  * the thread_struct is up to date for task tsk.
@@ -333,6 +367,9 @@ void enable_kernel_vsx(void)
 	unsigned long cpumsr;
 
 	WARN_ON(preemptible());
+	WARN_ON_ONCE(this_cpu_read(in_kernel_fpu));
+
+	this_cpu_write(in_kernel_fpu, true);
 
 	cpumsr = msr_check_and_set(MSR_FP|MSR_VEC|MSR_VSX);
 
@@ -354,6 +391,15 @@ void enable_kernel_vsx(void)
 }
 EXPORT_SYMBOL(enable_kernel_vsx);
 
+void disable_kernel_vsx(void)
+{
+	WARN_ON_ONCE(!this_cpu_read(in_kernel_fpu));
+
+	this_cpu_write(in_kernel_fpu, false);
+	msr_check_and_clear(MSR_FP|MSR_VEC|MSR_VSX);
+}
+EXPORT_SYMBOL(disable_kernel_vsx);
+
 void flush_vsx_to_thread(struct task_struct *tsk)
 {
 	if (tsk->thread.regs) {
@@ -406,6 +452,90 @@ void flush_spe_to_thread(struct task_struct *tsk)
 }
 #endif /* CONFIG_SPE */
 
+static bool fpu_support(void)
+{
+	if (cpu_has_feature(CPU_FTR_VSX_COMP)) {
+		return true;
+	} else if (cpu_has_feature(CPU_FTR_ALTIVEC_COMP)) {
+		return true;
+	} else if (!cpu_has_feature(CPU_FTR_FPU_UNAVAILABLE)) {
+		return true;
+	}
+
+	return false;
+}
+
+bool kernel_fpu_enabled(void)
+{
+	return this_cpu_read(in_kernel_fpu);
+}
+EXPORT_SYMBOL(kernel_fpu_enabled);
+
+void kernel_fpu_begin(void)
+{
+	if (!fpu_support()) {
+		WARN_ON_ONCE(1);
+		return;
+	}
+
+	preempt_disable();
+
+#ifdef CONFIG_VSX
+	if (cpu_has_feature(CPU_FTR_VSX_COMP)) {
+		enable_kernel_vsx();
+		return;
+	}
+#endif
+
+#ifdef CONFIG_ALTIVEC
+	if (cpu_has_feature(CPU_FTR_ALTIVEC_COMP)) {
+		enable_kernel_altivec();
+		return;
+	}
+#endif
+
+#ifdef CONFIG_PPC_FPU
+	if (!cpu_has_feature(CPU_FTR_FPU_UNAVAILABLE)) {
+		enable_kernel_fp();
+		return;
+	}
+#endif
+}
+EXPORT_SYMBOL_GPL(kernel_fpu_begin);
+
+void kernel_fpu_end(void)
+{
+	if (!fpu_support()) {
+		WARN_ON_ONCE(1);
+		return;
+	}
+
+#ifdef CONFIG_VSX
+	if (cpu_has_feature(CPU_FTR_VSX_COMP)) {
+		disable_kernel_vsx();
+		goto done;
+	}
+#endif
+
+#ifdef CONFIG_ALTIVEC
+	if (cpu_has_feature(CPU_FTR_ALTIVEC_COMP)) {
+		disable_kernel_altivec();
+		goto done;
+	}
+#endif
+
+#ifdef CONFIG_PPC_FPU
+	if (!cpu_has_feature(CPU_FTR_FPU_UNAVAILABLE)) {
+		disable_kernel_fp();
+		goto done;
+	}
+#endif
+
+done:
+	preempt_enable();
+}
+EXPORT_SYMBOL_GPL(kernel_fpu_end);
+
 static unsigned long msr_all_available;
 
 static int __init init_msr_all_available(void)
-- 
2.25.1

[RFC 2/2] drm/amd/display: Use PPC FPU functions

[Anson Jacob]

Use kernel_fpu_begin & kernel_fpu_end for PPC

Depends on "ppc/fpu: Add generic FPU api similar to x86"

Signed-off-by: Anson Jacob <Anson.Jacob@amd.com>
---
 drivers/gpu/drm/amd/display/dc/os_types.h | 28 ++---------------------
 1 file changed, 2 insertions(+), 26 deletions(-)

diff --git a/drivers/gpu/drm/amd/display/dc/os_types.h b/drivers/gpu/drm/amd/display/dc/os_types.h
index 126c2f3a4dd3..999c5103357e 100644
--- a/drivers/gpu/drm/amd/display/dc/os_types.h
+++ b/drivers/gpu/drm/amd/display/dc/os_types.h
@@ -57,32 +57,8 @@
 #define DC_FP_END() kernel_fpu_end()
 #elif defined(CONFIG_PPC64)
 #include <asm/switch_to.h>
-#include <asm/cputable.h>
-#define DC_FP_START() { \
-	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(); \
-	} \
-}
-#define DC_FP_END() { \
-	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
+#define DC_FP_START() kernel_fpu_begin()
+#define DC_FP_END() kernel_fpu_end()
 #endif
 
 /*
-- 
2.25.1

Re: [RFC 1/2] ppc/fpu: Add generic FPU api similar to x86

[Christoph Hellwig]

On Mon, Jul 19, 2021 at 03:52:10PM -0400, Anson Jacob wrote:
> - Add kernel_fpu_begin & kernel_fpu_end API as x86
> - Add logic similar to x86 to ensure fpu
>   begin/end call correctness
> - Add kernel_fpu_enabled to know if FPU is enabled
> 
> Signed-off-by: Anson Jacob <Anson.Jacob@amd.com>

All the x86 FPU support is EXPORT_SYMBOL_GPL for a good reason, so
please stick to that.

Re: [RFC 2/2] drm/amd/display: Use PPC FPU functions

[Christoph Hellwig]

>  #define DC_FP_END() kernel_fpu_end()
>  #elif defined(CONFIG_PPC64)
>  #include <asm/switch_to.h>
> +#define DC_FP_START() kernel_fpu_begin()
> +#define DC_FP_END() kernel_fpu_end()
>  #endif

Please use the same header as x86 in your first patch and then kill
this ifdefered and the DC_FP_START/DC_FP_END definitions entirely.

Re: [RFC 0/2] Add generic FPU api similar to x86

[Christian König]

While you already CCed a bunch of people stuff like that needs to go to 
the appropriate mailing list and not just amd-gfx.

Especially LKML so that other core devs can take a look as well.

Regards,
Christian.

Am 19.07.21 um 21:52 schrieb Anson Jacob:
> This is an attempt to have generic FPU enable/disable
> calls similar to x86.
> So that we can simplify gpu/drm/amd/display/dc/os_types.h
>
> Also adds FPU correctness logic seen in x86.
>
> Anson Jacob (2):
>    ppc/fpu: Add generic FPU api similar to x86
>    drm/amd/display: Use PPC FPU functions
>
>   arch/powerpc/include/asm/switch_to.h      |  29 ++---
>   arch/powerpc/kernel/process.c             | 130 ++++++++++++++++++++++
>   drivers/gpu/drm/amd/display/dc/os_types.h |  28 +----
>   3 files changed, 139 insertions(+), 48 deletions(-)
>

Re: [RFC 0/2] Add generic FPU api similar to x86

[Christophe Leroy]

Le 19/07/2021 à 21:52, Anson Jacob a écrit :
> This is an attempt to have generic FPU enable/disable
> calls similar to x86.
> So that we can simplify gpu/drm/amd/display/dc/os_types.h

Seems like gpu/drm/amd/display/dc/os_types.h has been simplified through 
another way via commit 96ee63730fa3 ("drm/amd/display: Add control 
mechanism for FPU")

Are powerpc changes in patch 1 still relevant ? In that case please rebase.

> 
> Also adds FPU correctness logic seen in x86.
> 
> Anson Jacob (2):
>    ppc/fpu: Add generic FPU api similar to x86
>    drm/amd/display: Use PPC FPU functions
> 
>   arch/powerpc/include/asm/switch_to.h      |  29 ++---
>   arch/powerpc/kernel/process.c             | 130 ++++++++++++++++++++++
>   drivers/gpu/drm/amd/display/dc/os_types.h |  28 +----
>   3 files changed, 139 insertions(+), 48 deletions(-)
>