On Thu, 22 Jun 2017 10:48:13 -0600 Logan Gunthorpe <logang@xxxxxxxxxxxx> wrote: > Currently, ioread64 and iowrite64 are only available io CONFIG_64BIT=y > and CONFIG_GENERIC_IOMAP=n. Thus, seeing the functions are not > universally available, it makes them unusable for driver developers. > This leads to ugly hacks such as those at the top of > > drivers/ntb/hw/intel/ntb_hw_intel.c > > This patch adds fallback implementations for when CONFIG_64BIT and > CONFIG_GENERIC_IOMAP are not set. These functions use two io32 based > calls to complete the operation. > > Note, we do not use the volatile keyword in these functions like the > others in the same file. It is necessary to avoid a compiler warning > on arm. This is a really really bad idea as per the Alpha comment. ioread64 and iowrite64 generate a single 64bit bus transaction. There is hardware where mmio operations have side effects so simply using a pair of 32bit operations blindly does not work (consider something as trivial as reading a 64bit performance counter or incrementing pointer). If a platform doesn't support 64bit I/O operations from the CPU then you either need to use some kind of platform/architecture specific interface if present or accept you don't have one. It's not safe to split it. Possibly for some use cases you could add an ioread64_maysplit() but you cannot blindly break ioread64/write64() and expect it to magically allow you to use drivers that depend upon it. What btw is the actual ARM compiler warning ? Is the compiler also trying to tell you it's a bad idea ? Alan
