Re: [PATCH v2 3/6] powerpc: Convert flush_icache_range & friends to C

[Michael Ellerman <mpe@ellerman.id.au>]

Christophe Leroy <christophe.leroy@c-s.fr> writes:
> Le 03/09/2019 à 07:23, Alastair D'Silva a écrit :
>> From: Alastair D'Silva <alastair@d-silva.org>
>> 
>> Similar to commit 22e9c88d486a
>> ("powerpc/64: reuse PPC32 static inline flush_dcache_range()")
>> this patch converts the following ASM symbols to C:
>>      flush_icache_range()
>>      __flush_dcache_icache()
>>      __flush_dcache_icache_phys()
>> 
>> This was done as we discovered a long-standing bug where the length of the
>> range was truncated due to using a 32 bit shift instead of a 64 bit one.
>> 
>> By converting these functions to C, it becomes easier to maintain.
>> 
>> flush_dcache_icache_phys() retains a critical assembler section as we must
>> ensure there are no memory accesses while the data MMU is disabled
>> (authored by Christophe Leroy). Since this has no external callers, it has
>> also been made static, allowing the compiler to inline it within
>> flush_dcache_icache_page().
>> 
>> Signed-off-by: Alastair D'Silva <alastair@d-silva.org>
>> Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
>> ---
>>   arch/powerpc/include/asm/cache.h      |  26 ++---
>>   arch/powerpc/include/asm/cacheflush.h |  24 ++--
>>   arch/powerpc/kernel/misc_32.S         | 117 --------------------
>>   arch/powerpc/kernel/misc_64.S         | 102 -----------------
>>   arch/powerpc/mm/mem.c                 | 152 +++++++++++++++++++++++++-
>>   5 files changed, 173 insertions(+), 248 deletions(-)
>> 
>> diff --git a/arch/powerpc/include/asm/cache.h b/arch/powerpc/include/asm/cache.h
>> index f852d5cd746c..91c808c6738b 100644
>> --- a/arch/powerpc/include/asm/cache.h
>> +++ b/arch/powerpc/include/asm/cache.h
>> @@ -98,20 +98,7 @@ static inline u32 l1_icache_bytes(void)
>>   #endif
>>   #endif /* ! __ASSEMBLY__ */
>>   
>> -#if defined(__ASSEMBLY__)
>> -/*
>> - * For a snooping icache, we still need a dummy icbi to purge all the
>> - * prefetched instructions from the ifetch buffers. We also need a sync
>> - * before the icbi to order the the actual stores to memory that might
>> - * have modified instructions with the icbi.
>> - */
>> -#define PURGE_PREFETCHED_INS	\
>> -	sync;			\
>> -	icbi	0,r3;		\
>> -	sync;			\
>> -	isync
>> -
>> -#else
>> +#if !defined(__ASSEMBLY__)
>>   #define __read_mostly __attribute__((__section__(".data..read_mostly")))
>>   
>>   #ifdef CONFIG_PPC_BOOK3S_32
>> @@ -145,6 +132,17 @@ static inline void dcbst(void *addr)
>>   {
>>   	__asm__ __volatile__ ("dcbst %y0" : : "Z"(*(u8 *)addr) : "memory");
>>   }
>> +
>> +static inline void icbi(void *addr)
>> +{
>> +	__asm__ __volatile__ ("icbi 0, %0" : : "r"(addr) : "memory");
>
> I think "__asm__ __volatile__" is deprecated. Use "asm volatile" instead.

Yes please.

>> diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c
>> index 9191a66b3bc5..cd540123874d 100644
>> --- a/arch/powerpc/mm/mem.c
>> +++ b/arch/powerpc/mm/mem.c
>> @@ -321,6 +321,105 @@ void free_initmem(void)
>>   	free_initmem_default(POISON_FREE_INITMEM);
>>   }
>>   
>> +/*
>> + * Warning: This macro will perform an early return if the CPU has
>> + * a coherent icache. The intent is is call this early in function,
>> + * and handle the non-coherent icache variant afterwards.
>> + *
>> + * For a snooping icache, we still need a dummy icbi to purge all the
>> + * prefetched instructions from the ifetch buffers. We also need a sync
>> + * before the icbi to order the the actual stores to memory that might
>> + * have modified instructions with the icbi.
>> + */
>> +#define flush_coherent_icache_or_return(addr) {			\
>> +	if (cpu_has_feature(CPU_FTR_COHERENT_ICACHE)) {		\
>> +		mb(); /* sync */				\
>> +		icbi(addr);					\
>> +		mb(); /* sync */				\
>> +		isync();					\
>> +		return;						\
>> +	}							\
>> +}
>
> I hate this kind of awful macro which kills code readability.

Yes I agree.

> Please to something like
>
> static bool flush_coherent_icache_or_return(unsigned long addr)
> {
> 	if (!cpu_has_feature(CPU_FTR_COHERENT_ICACHE))
> 		return false;
>
> 	mb(); /* sync */
> 	icbi(addr);
> 	mb(); /* sync */
> 	isync();
> 	return true;
> }
>
> then callers will do:
>
> 	if (flush_coherent_icache_or_return(addr))
> 		return;

I don't think it needs the "_or_return" in the name.

eg, it can just be:

 	if (flush_coherent_icache(addr))
		return;


Which reads fine I think, ie. flush the coherent icache, and if that
succeeds return, else continue.

cheers