Hi, Sam, On Mon, May 21, 2018 at 05:08:03PM +0200, Sam Ravnborg wrote: > Hi Peter. > > On Mon, May 21, 2018 at 02:54:34PM +0300, Peter Mamonov wrote: > > Signed-off-by: Peter Mamonov <pmamonov@xxxxxxxxx> > > --- > > Can you elaborate a little over this change? > Earlier IOMEM was fixed to use KSEG1 and not CKSEG1 > > And now something else moves the other way. Well, before patch 6 of this patch series IOMEM for MIPS was defined using CKSEG1ADDR() macro. Patch 6 introduced a new definition for MIPS64 using PHYS_TO_XKSEG_UNCACHED macro. I can't see any use of KSEG1 in IOMEM definition for MIPS... > > For readers like me that has no clue what KSEG0 and CKSEG0 > is the change looks like noise. > It may be perfectly fine, but there is no backgrond info to tell why Anyway, here is the story. MIPS virtual address space is partitioned into several segments. Here is an excerpt from the "See MIPS run (Linux)" book which describes KSEG0 and KSEG1: kseg0 0x8000.0000 – 9FFF.FFFF (512MB): These addresses are translated into physical addresses by merely stripping off the top bit and mapping them contiguously into the low 512 MB of physical memory. [...] Addresses in this region are almost always accessed through the cache, so they may not be used until the caches are properly initialized. They will be used for most programs and data in systems not using the MMU and will be used for the OS kernel for systems that do use the MMU. kseg1 0xA000.0000 – BFFF.FFFF (512MB): These addresses are mapped into physical addresses by stripping off the leading 3 bits, giving a duplicate mapping of the low 512 MB of physical memory. But this time, access will not use the cache. The kseg1 region is the only chunk of the memory map that is guaranteed to behave properly from system reset; that’s why the after-reset starting point ( 0xBFC0.0000 ) lies within it. Now, after introduction of MIPS64 these segments were preserved for compatibility reasons, and its 64bit equivalents are located at 0xffffffff80000000 and 0xffffffffa0000000 respectively. As you can see from the arch/mips/include/asm/addrspace.h KSEG0/1 are defined for 32 bits only: #ifdef CONFIG_64BIT ... #else ... #define KSEG0 0x80000000 #define KSEG1 0xa0000000 ... #endif While CKSEG0/1 are defined for both 64 and 32 bits: #ifdef CONFIG_64BIT ... #define CKSEG0 _CONST64_(0xffffffff80000000) #define CKSEG1 _CONST64_(0xffffffffa0000000) ... #else ... #define CKSEG0 0x80000000 #define CKSEG1 0xa0000000 ... #endif Linux defines these constants in the same way. I belive the "C" prefix to contants names stands for Compatible. Anyway, if you try to compile 64 bit barebox and use KSEG1 in your code, compilation will fail. Regards, Peter > > Sam _______________________________________________ barebox mailing list barebox@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/barebox
