Le 21/10/2011 23:54, Simon Glass a écrit : > Hi Albert, > > On Fri, Oct 21, 2011 at 2:43 PM, Albert ARIBAUD > <albert.u.b...@aribaud.net> wrote: >> Le 21/10/2011 23:18, Simon Glass a écrit : >>> >>> Hi Albert, >>> >>> On Fri, Oct 21, 2011 at 1:58 PM, Albert ARIBAUD >>> <albert.u.b...@aribaud.net> wrote: >>>> >>>> Le 13/10/2011 23:05, Simon Glass a écrit : >>>>> >>>>> Some SOCs have do not start up with their 'main' CPU. The first U-Boot >>>>> code may then be executed with a CPU which does not have a CP15, or not >>>>> a >>>>> useful one. >>>>> >>>>> Here we split the initialization of CP15 into a separate call, which can >>>>> be performed later if required. >>>>> >>>>> Once the main CPU is running, you should call cpu_init_cp15() to perform >>>>> this init as early as possible. >>>>> >>>>> Existing ARMv7 boards which define CONFIG_SKIP_LOWLEVEL_INIT should not >>>>> need to change, this CP15 init is still skipped in that case. The only >>>>> impact for these boards is that the cpu_init_cp15() will be available >>>>> even if it is never used on these boards. >>>> >>>> I'm not too sure I understand how this is working: if you are moving cp15 >>>> init to later, it will still be done by the same core that would have >>>> done >>>> it earlier, won't it? >>>> >>>> IOW, I would like to better understand how this boot core/main core >>>> business >>>> works. How does the main core start execution? At which address? Does it >>>> go >>>> through its reset vector? Do the cores share the same location for reset >>>> vectors? Etc. >>> >>> For Tegra is it like this: >>> >>> The ARM7 CPU (called AVP for Audio Video Processor) starts up first. >>> It runs the boot ROM and then U-Boot and gets as far as >>> arch_cpu_init(). The AVP does not have a CP15 or a cache so cannot run >>> the CP15 init code. The AVP then starts up the first Cortex-A9 (an >>> ARMv7 architecture CPU). This CPU (the main core, if you like) starts >>> from the same address as the first one (i.e. the start of U-Boot). It >>> is as if this is the core that we really wanted to use, but it wasn't >>> available initially. This main core runs through arch_cpu_init() and >>> sails into board_init_f(). At this point no CP15 init has been done. >> >> Thanks. So what this amounts to is, both cores will run the same binary, and >> I assume the AVP will shut itself off once the A9 runs. But what I don't get > > Yes > >> is, if A9 goes through the same sequence of code as AVP, then it will >> execute cp15 where is is not, won't it? > > On Tegra we have CONFIG_SKIP_LOWLEVEL_INIT set to avoid this. That > much is already supported by U-Boot.
I still don't get it: if you have lowlevel init skipped for one core, it will be for the other as well. >> Anyway: your patch moves cp15 init far enough that the AVP won't execute it, >> but the A9 will. > > Well, on Tegra we call the cp15 init directly when it is safe to do so, later. > >> >> Only, what will happen when another multiple-core ARM SoC gets U-Boot >> support but the location you chose for cp15 init is inadequate for it? Shall >> we move cp15 init again, and where? > > If CONFIG_SKIP_LOWLEVEL_INIT is not defined, then the low level init > will operate exactly as now. My patch effectively just allows you to > have CONFIG_SKIP_LOWLEVEL_INIT but later call part of that lowlevel > init. In my view, the cp15 init should not be lumped in with the > 'memory init' or whatever else it expected to be done in the lowlevel > init. I think I get the point: due to the fact that both cores run the same starup code path, and due to the fact that they run it one after the other and share a lot of devices, at mots one of them shoud perform low level inits (e.g. RAM init), and some low-level inits can only be performed by one of them (e.g., cp15). >> I'd prefer the cp15 init to stay where it is but execute only for A9, for >> instance by checking some core identification register. > > Well I actually haven't moved it! It is just that previously it was > impossible to call cp15_init from anywhere later. It is moved, in that it belongs to low level init... of A9. > What you say can be done, it would involve some assembler though and > would need to be another CONFIG option. Was trying to avoid adding new > assembler. Low level init is about assembler and, well, low level. :) But I don't see why there should be another CONFIG option. IIUC, you should be able to do with only CONFIG_SKIP_LOWLEVEL_INIT: within the low level init code under it, you would do the equivalent of a switch, with one branch for AVM (and DDR init etc) and one branch for A9 (with cp15 init etc). > Regards, > Simon Amicalement, -- Albert. _______________________________________________ U-Boot mailing list U-Boot@lists.denx.de http://lists.denx.de/mailman/listinfo/u-boot
