[PATCH] Revert "arm: bootm: Disable LMB reservation for command line and board info on arm64"

[Marek Vasut]

On 7/29/21 5:23 PM, Tom Rini wrote:
> On Thu, Jul 29, 2021 at 05:01:09PM +0200, Marek Vasut wrote:
>> On 7/29/21 9:22 AM, Jan Kiszka wrote:
>>> From: Jan Kiszka <jan.kiszka at siemens.com>
>>>
>>> This reverts commit 2359fa7a87848626bcbd3399e92c657595880cd7.
>>>
>>> While the goal is valid and there is surely unused memory in that area,
>>> we also have a lot of crucial things still located at the top-of-memory
>>> while running lmb_alloc_base. Such things are the page table (tlb_addr),
>>> relocated U-Boot and the active stack. Possibly more. So this patch was
>>> premature, we will need relocations of those things first if we want to
>>> use the range.
>>>
>>> Fixes booting on the IOT2050, but likely also on other boards. It got
>>> stuck on relocating the FDT - over the relocated U-Boot code.
>>>
>>> Signed-off-by: Jan Kiszka <jan.kiszka at siemens.com>
>>> ---
>>>
>>> Practically,
>>>
>>> void arch_lmb_reserve(struct lmb *lmb)
>>> {
>>> 	lmb_reserve(lmb, gd->relocaddr, gd->ram_top - gd->relocaddr);
>>> }
>>
>> So this is wrong and breaks a use case on rcar3, where there is more stuff
>> which should not be reserved until the ram top.
>>
>> I suspect the real fix here is to protect only the stack and tlb on arm64,
>> not just everything from current stack bottom to ram top ?
> 
> Wait, what?  There's never been a U-Boot release that didn't reserve
> that area

That does not mean such a huge reservation is correct.

I apologize for not being overly clear in my answer, I already told Jan 
I am highly overloaded and simply lack the capacity to analyze this 
problem thoroughly on a short notice.

> so when did rcar3 introduce something there that shouldn't be
> reserved?  And you had phrased this to me on IRC as about reserving spot
> for ATAGS, and that not being needed of course on arm64.  But that's not
> what's going on.  Perhaps the answer is that rcar3 needs to introduce a
> board_lmb_reserve to free the normal arch one and provide whatever more
> narrow scope it needs.

Based on the commit message 2359fa7a878 ("arm: bootm: Disable LMB 
reservation for command line and board info on arm64") , this is about 
ATAGS and we really don't need to reserve those on arm64.

I didn't hit the tlb reservation issue Jan has in my tests on rcar3, so 
I suspect that is the real problem here, i.e. we need some more fine 
grained lmb reservation on arm64 ?