Hi Robin, > -----Original Message----- > From: Robin Murphy [mailto:robin.mur...@arm.com] > Sent: Saturday, July 30, 2016 2:06 AM > To: 이광우(LEE KWANGWOO) MS SW; Russell King - ARM Linux; Catalin Marinas; Will > Deacon; Mark Rutland; > linux-arm-ker...@lists.infradead.org > Cc: 김현철(KIM HYUNCHUL) MS SW; linux-kernel@vger.kernel.org; 정우석(CHUNG WOO SUK) > MS SW > Subject: Re: [PATCH v2] arm64: mm: convert __dma_* routines to use start, size > > On 28/07/16 01:08, kwangwoo....@sk.com wrote: > >> -----Original Message----- > >> From: Robin Murphy [mailto:robin.mur...@arm.com] > >> Sent: Wednesday, July 27, 2016 6:56 PM > >> To: 이광우(LEE KWANGWOO) MS SW; Russell King - ARM Linux; Catalin Marinas; > >> Will Deacon; Mark Rutland; > >> linux-arm-ker...@lists.infradead.org > >> Cc: 김현철(KIM HYUNCHUL) MS SW; linux-kernel@vger.kernel.org; 정우석(CHUNG WOO > >> SUK) MS SW > >> Subject: Re: [PATCH v2] arm64: mm: convert __dma_* routines to use start, > >> size > >> > >> On 27/07/16 02:55, kwangwoo....@sk.com wrote: > >> [...] > >>>>> /* > >>>>> - * __dma_clean_range(start, end) > >>>>> + * __dma_clean_area(start, size) > >>>>> * - start - virtual start address of region > >>>>> - * - end - virtual end address of region > >>>>> + * - size - size in question > >>>>> */ > >>>>> -__dma_clean_range: > >>>>> - dcache_line_size x2, x3 > >>>>> - sub x3, x2, #1 > >>>>> - bic x0, x0, x3 > >>>>> -1: > >>>>> +__dma_clean_area: > >>>>> alternative_if_not ARM64_WORKAROUND_CLEAN_CACHE > >>>>> - dc cvac, x0 > >>>>> + dcache_by_line_op cvac, sy, x0, x1, x2, x3 > >>>>> alternative_else > >>>>> - dc civac, x0 > >>>>> + dcache_by_line_op civac, sy, x0, x1, x2, x3 > >>>> > >>>> dcache_by_line_op is a relatively large macro - is there any way we can > >>>> still apply the alternative to just the one instruction which needs it, > >>>> as opposed to having to patch the entire mostly-identical routine? > >>> > >>> I agree with your opinion. Then, how do you think about using CONFIG_* > >>> options > >>> like below? I think that alternative_* macros seems to keep the space for > >>> unused instruction. Is it necessary? Please, share your thought about the > >>> space. Thanks! > >>> > >>> +__dma_clean_area: > >>> +#if defined(CONFIG_ARM64_ERRATUM_826319) || \ > >>> + defined(CONFIG_ARM64_ERRATUM_827319) || \ > >>> + defined(CONFIG_ARM64_ERRATUM_824069) || \ > >>> + defined(CONFIG_ARM64_ERRATUM_819472) > >>> + dcache_by_line_op civac, sy, x0, x1, x2, x3 > >>> +#else > >>> + dcache_by_line_op cvac, sy, x0, x1, x2, x3 > >>> +#endif > >> > >> That's not ideal, because we still only really want to use the > >> workaround if we detect a CPU which needs it, rather than baking it in > >> at compile time. I was thinking more along the lines of pushing the > >> alternative down into dcache_by_line_op, something like the idea below > >> (compile-tested only, may not actually be viable). > > > > OK. Using the capability of CPU features seems to be preferred. > > > >> Robin. > >> > >> -----8<----- > >> diff --git a/arch/arm64/include/asm/assembler.h > >> b/arch/arm64/include/asm/assembler.h > >> index 10b017c4bdd8..1c005c90387e 100644 > >> --- a/arch/arm64/include/asm/assembler.h > >> +++ b/arch/arm64/include/asm/assembler.h > >> @@ -261,7 +261,16 @@ lr .req x30 // link register > >> add \size, \kaddr, \size > >> sub \tmp2, \tmp1, #1 > >> bic \kaddr, \kaddr, \tmp2 > >> -9998: dc \op, \kaddr > >> +9998: > >> + .ifeqs "\op", "cvac" > >> +alternative_if_not ARM64_WORKAROUND_CLEAN_CACHE > >> + dc cvac, \kaddr > >> +alternative_else > >> + dc civac, \kaddr > >> +alternative_endif > >> + .else > >> + dc \op, \kaddr > >> + .endif > >> add \kaddr, \kaddr, \tmp1 > >> cmp \kaddr, \size > >> b.lo 9998b > > > > I agree that it looks not viable because it makes the macro bigger and > > conditional specifically with CVAC op. > > Actually, having had a poke around in the resulting disassembly, it > looks like this does work correctly. I can't think of a viable reason > for the whole dcache_by_line_op to ever be wrapped in yet another > alternative (which almost certainly would go horribly wrong), and it > would mean that any other future users are automatically covered for > free. It's just horrible to look at at the source level.
Then, Are you going to send a patch for this? Or should I include this change? > Robin. > > > > > Then.. if the number of the usage of alternative_* macros for erratum is > > few (just one in this case for cache clean), I think only small change like > > below seems to be optimal and there is no need to create a variant macro of > > dcache_cache_by_line_op. How do you think about it? [...] Regards, Kwangwoo
