On Fri, 21 Jun 2019, Arnd Bergmann wrote: > > The use of 64-bit operations to access option's packet memory, which is > > true SRAM, i.e. no side effects, is to improve throughput only and there's > > no need for atomicity here nor also any kind of barriers, except at the > > conclusion. Splitting 64-bit accesses into 32-bit halves in software > > would not be a functional error here. > > The other property of packet memory and similar things is that you > basically want memcpy()-behavior with no byteswaps. This is one > of the few cases in which __raw_readq() is actually the right accessor > in (mostly) portable code.
Correct, but we're missing an `__raw_readq_relaxed', etc. interface and having additional barriers applied on every access would hit performance very badly; in fact even the barriers `*_relaxed' accessors imply would best be removed in this use (which is why defza.c uses `readw_o' vs `readw_u', etc. internally), but after all the struggles over the years for weakly ordered internal APIs x86 people are so averse to I'm not sure if I want to start another one. We can get away with `readq_relaxed' in this use though as all the systems this device can be used with are little-endian as is TURBOchannel, so no byte-swapping will ever actually occur. Maciej
