On Mon, 30 Nov 2015, Pali Rohár wrote: > On Monday 30 November 2015 07:23:53 Tony Lindgren wrote: > > * Pali Rohár <pali.rohar@xxxxxxxxx> [151129 16:16]: > > > On Monday 30 November 2015 01:09:17 Nicolas Pitre wrote: > > > > On Sun, 29 Nov 2015, Russell King - ARM Linux wrote: > > > > > On Sat, Nov 28, 2015 at 12:34:23PM -0500, Nicolas Pitre wrote: > > > > > > Good. And Arnd likes the idea too. So we might be converging at > > > > > > last which is a good thing. > > > > > > > > > > I disagree with the idea that there is convergence. There might be > > > > > convergence towards an idea, but... Here's a mail extract, from > > > > > July 7th, from earlier in this very thread: > > > > > > > > > > Pali: > > > > > > Me: > > > > > > > Are the ATAGs at a fixed address on the N900? > > > > > > > > > > > > Yes, in board-rx51.c is: > > > > > > > > > > > > .atag_offset = 0x100 > > > > > > > > > > > > and Nokia Bootloader (proprietary) store them to that address. > > > > > > > > > > > > > Can that be handled in > > > > > > > some kind of legacy file for the N900 which calls save_atags() > > > > > > > on it, so we don't end up introducing yet more stuff that we > > > > > > > have to maintain into the distant future? If not, what about > > > > > > > copying a known working atag structure into a legacy file for > > > > > > > the N900? > > > > > > > > > > > > I already asked question if it is possible to read ATAGs from DT > > > > > > booted kernel. And somebody (do not remember who) wrote to ML, > > > > > > that it is not possible and it can be done in that uncompress > > > > > > code. > > > > > > > > Who is that somebody? If ever it happened to be me then objection is > > > > withdrawn. Otherwise that somebody should come forth and speak up > > > > again. > > > > > > > > > > ... do not remember ... this discussion were in more email threads and > > > takes more then one year... sorry but my memory is not excellent > > > > Yes this certainly seems like the best solution. I think we got into > > the atags-to-dt track as some of the atags are already being translated. > > > > In this case there's no need to translate them AFAIK. You can just > > parse them and have them available for the user space. So as long as > > nothing trashes the atags at the atag_offset, you should be able to > > call a function to parse them in the n900 specific init_machine. > > > > Regards, > > > > Tony > > In arch/arm/kernel/setup.c is function setup_arch() and it calls: > > mdesc = setup_machine_fdt(__atags_pointer); > if (!mdesc) > mdesc = setup_machine_tags(__atags_pointer, __machine_arch_type); > > So it looks like that on atags address is stored either atags structure > or DT structure... so it is truth kernel uncompress code put DT blob to > same offset where is expected atags structure? No. It doesn't put it anywhere. Those functions read DT/ATAGs from the passed address. But you know this address won't be the one you want for the legacy ATAGs. What you should do is to add a init_early hook to your mdesc structure and retrieve your ATAGs from there directly at PAGE_OFFSET + 0x100. Now I suspect paging_init() marks the point where the ATAGs will be overwritten. To prevent this, you might have to add an additional tweak in arm_mm_memblock_reserve() similar to the one already present for CONFIG_SA1111. Something like: memblock_reserve(PHYS_OFFSET, PAGE_SIZE); And later on you can return that page back to the system. Nicolas
