Hi Alex, On 15 September 2018 at 10:16, Alexander Graf <ag...@suse.de> wrote: > > > On 14.09.18 17:46, Simon Glass wrote: >> Hi Alex, >> >> On 26 August 2018 at 19:11, Alexander Graf <ag...@suse.de> wrote: >>> >>> >>> On 08.08.18 11:54, Simon Glass wrote: >>>> At present map_sysmem() maps an address into the sandbox RAM buffer, >>>> return a pointer, while map_to_sysmem() goes the other way. >>>> >>>> The mapping is currently just 1:1 since a case was not found where a more >>>> flexible mapping was needed. PCI does have a separate and more complex >>>> mapping, but uses its own mechanism. >>>> >>>> However this arrange cannot handle one important case, which is where a >>>> test declares a stack variable and passes a pointer to it into a U-Boot >>>> function which uses map_to_sysmem() to turn it into a address. Since the >>>> pointer is not inside emulated DRAM, this will fail. >>>> >>>> Add a mapping feature which can handle any such pointer, mapping it to a >>>> simple tag value which can be passed around in U-Boot as an address. >>>> >>>> Signed-off-by: Simon Glass <s...@chromium.org> >>> >>> I think you are aware that this logic will fall apart spectacularly if >>> any arithmetic operation happens on the virtual (U-Boot) address, right? >>> So simple code like >>> >>> readl(vaddr + 1); >>> >>> will just fail (hopefully) or (more likely) return a completely >>> incorrect value. >>> >>> I assume this is intentional, but shouldn't the tag increment be >>> something slightly larger then? >> >> What do you expect readl() to do on sandbox? At present it is just a >> no-op. I suppose we could support memory-mapped I/O but it has not >> been attempted yet. > > It was really just meant as an arbitrary example of something where you > assume "address + 1" == "pointer(address) + 1".
So long as the addresses are within the range sandbox supports (normally 0 to 128MB unless you increase RAM size) then there is no problem adding 1 to either an address (or a pointer derived from it with map_sysmem()). If you use an address outside that range, it is actually a tag, not an address. Trying to use an out-of-range address is invalid anyway, so it probably doesn't matter. Regards, Simon _______________________________________________ U-Boot mailing list U-Boot@lists.denx.de https://lists.denx.de/listinfo/u-boot
