[RFC PATCH 3/5] powerpc/64s: add CONFIG_PPC_NMMU for nest MMU support

[Christophe Leroy]

Le 20/12/2020 à 00:48, Nicholas Piggin a écrit :
> This allows some nest MMU features to be compiled away if coprocessor
> support is not selected.
> 
> Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
> ---
>   arch/powerpc/Kconfig                          | 1 +
>   arch/powerpc/include/asm/book3s/64/mmu.h      | 2 ++
>   arch/powerpc/include/asm/book3s/64/tlbflush.h | 2 ++
>   arch/powerpc/include/asm/mmu_context.h        | 5 +++--
>   arch/powerpc/platforms/Kconfig                | 3 +++
>   arch/powerpc/platforms/powernv/Kconfig        | 1 +
>   6 files changed, 12 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> index ae7391627054..4376bf4c53b4 100644
> --- a/arch/powerpc/Kconfig
> +++ b/arch/powerpc/Kconfig
> @@ -888,6 +888,7 @@ config PPC_PROT_SAO_LPAR
>   
>   config PPC_COPRO_BASE
>   	bool
> +	select PPC_NMMU if PPC_BOOK3S_64
>   
>   config SCHED_SMT
>   	bool "SMT (Hyperthreading) scheduler support"
> diff --git a/arch/powerpc/include/asm/book3s/64/mmu.h b/arch/powerpc/include/asm/book3s/64/mmu.h
> index 995bbcdd0ef8..07850d68a624 100644
> --- a/arch/powerpc/include/asm/book3s/64/mmu.h
> +++ b/arch/powerpc/include/asm/book3s/64/mmu.h
> @@ -103,8 +103,10 @@ typedef struct {
>   	/* Number of bits in the mm_cpumask */
>   	atomic_t active_cpus;
>   
> +#ifdef CONFIG_PPC_NMMU
>   	/* Number of users of the external (Nest) MMU */
>   	atomic_t copros;
> +#endif
>   
>   	/* Number of user space windows opened in process mm_context */
>   	atomic_t vas_windows;
> diff --git a/arch/powerpc/include/asm/book3s/64/tlbflush.h b/arch/powerpc/include/asm/book3s/64/tlbflush.h
> index 0a7431e954c6..c70a82851f78 100644
> --- a/arch/powerpc/include/asm/book3s/64/tlbflush.h
> +++ b/arch/powerpc/include/asm/book3s/64/tlbflush.h
> @@ -16,8 +16,10 @@ enum {
>   
>   static inline bool mm_has_nmmu(struct mm_struct *mm)
>   {
> +#ifdef CONFIG_PPC_NMMU
>   	if (unlikely(atomic_read(&mm->context.copros) > 0))
>   		return true;
> +#endif
>   	return false;
>   }
>   
> diff --git a/arch/powerpc/include/asm/mmu_context.h b/arch/powerpc/include/asm/mmu_context.h
> index d5821834dba9..53eac0cc4929 100644
> --- a/arch/powerpc/include/asm/mmu_context.h
> +++ b/arch/powerpc/include/asm/mmu_context.h
> @@ -143,6 +143,7 @@ static inline void dec_mm_active_cpus(struct mm_struct *mm)
>   	atomic_dec(&mm->context.active_cpus);
>   }
>   
> +#ifdef CONFIG_PPC_NMMU
>   static inline void mm_context_add_copro(struct mm_struct *mm)
>   {
>   	/*
> @@ -187,6 +188,7 @@ static inline void mm_context_remove_copro(struct mm_struct *mm)
>   			dec_mm_active_cpus(mm);
>   	}
>   }
> +#endif
>   
>   /*
>    * vas_windows counter shows number of open windows in the mm
> @@ -218,8 +220,7 @@ static inline void mm_context_remove_vas_window(struct mm_struct *mm)
>   #else
>   static inline void inc_mm_active_cpus(struct mm_struct *mm) { }
>   static inline void dec_mm_active_cpus(struct mm_struct *mm) { }
> -static inline void mm_context_add_copro(struct mm_struct *mm) { }
> -static inline void mm_context_remove_copro(struct mm_struct *mm) { }

Are you sure you can remove those ?
If so, I think it belongs to another patch, I can't see how the new PPC_NMMU would allow that by itself.

> +static inline bool mm_has_nmmu(struct mm_struct *mm) { return false; }
>   #endif
>   
>   
> diff --git a/arch/powerpc/platforms/Kconfig b/arch/powerpc/platforms/Kconfig
> index 7a5e8f4541e3..b4b04b3f98d1 100644
> --- a/arch/powerpc/platforms/Kconfig
> +++ b/arch/powerpc/platforms/Kconfig
> @@ -191,6 +191,9 @@ config PPC_INDIRECT_MMIO
>   config PPC_IO_WORKAROUNDS
>   	bool
>   
> +config PPC_NMMU
> +	bool
> +
>   source "drivers/cpufreq/Kconfig"
>   
>   menu "CPUIdle driver"
> diff --git a/arch/powerpc/platforms/powernv/Kconfig b/arch/powerpc/platforms/powernv/Kconfig
> index 619b093a0657..145009d74457 100644
> --- a/arch/powerpc/platforms/powernv/Kconfig
> +++ b/arch/powerpc/platforms/powernv/Kconfig
> @@ -36,6 +36,7 @@ config PPC_MEMTRACE
>   config PPC_VAS
>   	bool "IBM Virtual Accelerator Switchboard (VAS)"
>   	depends on PPC_POWERNV && PPC_64K_PAGES
> +	select PPC_NMMU
>   	default y
>   	help
>   	  This enables support for IBM Virtual Accelerator Switchboard (VAS).
>