Am 06.03.2016 um 20:53 schrieb Matthias Schiffer: > On 03/06/2016 08:38 PM, Daniel Schwierzeck wrote: >> >> >> Am 05.03.2016 um 04:15 schrieb Matthias Schiffer: >>> The "R" constraint supplies the address of an variable in a register. Use >>> "r" instead and adjust asm to supply the content of addr in a register >>> instead. >>> >>> Fixes: 2b8bcc5a ("MIPS: avoid .set ISA for cache operations") >>> Signed-off-by: Matthias Schiffer <mschif...@universe-factory.net> >>> Cc: Paul Burton <paul.bur...@imgtec.com> >>> Cc: Daniel Schwierzeck <daniel.schwierz...@gmail.com> >>> --- >>> >>> Hi, >>> I've noticed this when reading the code to understand how the cache >>> instruction is used. I'm not sure if this bug had any practical >>> consequences, or if nowadays all relevant compilers have >>> __builtin_mips_cache anyways. >>> >>> Please keep me in Cc in follow-up mails, I'm not subscribed to the u-boot >>> ML. >>> >>> Matthias >> >> I've disabled the builtin code and compared dissaemblies with and without >> your patch. Without your patch, gcc adds an additional store instruction >> before each cache instruction. >> >> E.g. for flush_dcache_range(): >> >> 18: afa20008 sw v0,8(sp) >> 1c: bfb50008 cache 0x15,8(sp) >> >> vs. >> >> 14: bc550000 cache 0x15,0(v0) >> >> The cache operation works anyway, but with your patch better code is >> generated. > > If I understand this correctly, the code without my patch would rather > invalidate the cache for the address 8(sp), which is part of the stack, > and not the memory pointed at by v0.
"sw v0,8(sp)" stores the address in v0 on the stack (location is current stack pointer + 8 * 4 bytes). The cache op then loads this address from stack. Eventually the cache op always uses the address stored in v0 so there is/was no functional bug. But the extra copy to the stack causes a performance degradation. -- - Daniel _______________________________________________ U-Boot mailing list U-Boot@lists.denx.de http://lists.denx.de/mailman/listinfo/u-boot