On 14/12/12 15:54, Jon Medhurst (Tixy) wrote: > On Fri, 2012-12-14 at 10:10 -0500, Christoffer Dall wrote: >> On Fri, Dec 14, 2012 at 3:49 AM, Jon Medhurst (Tixy) <tixy@xxxxxxxxxx> wrote: >>> On Thu, 2012-12-13 at 13:52 -0800, Christoffer Dall wrote: >>>> On Friday, December 7, 2012, Jon Medhurst (Tixy) wrote: >>>> >>>>> To enable CPU hotplug the need to provide some boot code at the >>>> reset >>>>> vector and which survives after the kernel has booted without being >>>>> overwritten. We achieve this by the getting the linker script to >>>> place >>>>> the code in boot.S at address zero. This now means we can delete the >>>>> code that relocates the secondary CPU pen code to "a location less >>>>> likely to be overridden". >>>>> >>>> >>>> not knowing these dev boards's memory maps I assume that the sysflags >>>> are >>>> initialized to 0 >>> >>> That's what the TRM says and what is observed in practice. >>> >>>> and that the first part of the physical memory space is >>>> reserved for secure access? >>> >>> Wasn't quite sure what you meant my that, so looked at the RTSM manual >>> for 'security' and spotted that if you enable the 'secure_memory' >>> option, then the NOR flash at address 0 is "Secure RO, aborts on >>> non-secure accesses". So if we need to support that option (do we?) then >>> my patch is broken. >>> >> we probably don't need this for vexpress in any situation that uses >> the boot-wrapper would be my guess, and we can always fix later then. >> >> What I was trying to figure out was why you can get rid of the "a >> location less likely to be overridden" and why you're sure this memory >> stays unmodified - I thought that was because you were loading the >> code in the beginning of the physical memory space, which wouldn't be >> touched by the linux kernel (i.e. reserved for the secure side), but >> my guess may have been wrong and I was never a whiz with linker >> scripts. > > In the RTSM manual, the first 64Mb of physical memory space is marked as > "NOR FLASH0", as it is on real hardware. This is flash memory which is > read-only under normal circumstances, and not anything Linux would go > poking about in, unless you configured an MTD device and used it for a > file system. > > DRAM is in the top 2GB and is what Linux uses for memory, and where most > of the bootwrapper still lives. The only bit I've relocated to the > bottom of the address space is everything in boot.S which includes all > the bits we need to survive after Linux boots in order to handle a cpu > startup again after being powered down then up again. > > Are you convinced, or do you still have concerns? > > I must admit, my patch is based on someone elses work, and I've not seen > documentation which says that NOR flash can be written to simply by the > application being loaded by the models having code located at the > relevant address. I do know, that this code works on both A15 and A15xA7 > models to boot Linux and Android, and that the new support it provides > for power down and up cores works. > > I'll try and see if I can find out if locating code at address zero is > officially supported... In the horrible hack that I use to boot both TC2 and RTSM, I use the static RAM located at 0x2E000000. It is only 64kB though. M. -- Jazz is not dead. It just smells funny... _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/cucslists/listinfo/kvmarm
