Hi Simon,
On Thu, Jan 22, 2015 at 11:42 AM, Simon Glass sjg@chromium.org wrote:
Hi Bin,
In the Baytrail FSP docs I see a note about the HOB passing back the 'Boot Loader Temporary Memory Data HOB'. This seems to be a copy of the entire temporary memory space. I wonder if we could recover struct global_data from this?
Yes, I think so. And I have verified this temporary memory space indeed contains stack contents before fsp_init() from U-Boot shell on Crown Bay. But the overall process might be complicated. See below.
If so, then we could move the fsp_init stuff to dram_init(), perhaps?
But perhaps this is a feature of only this FSP?
I believe this is a feature defined by the FSP architecture spec, so every FSP should support that.
Technically it should be no problem to call fsp_init() from arch_cpu_init() or even later dram_init(). However, I would say doing so brings us more harm than good. The following points are what I thought about before:
1). fsp_init() takes one parameter 'stack_top' to setup another stack after DRAM is initialized. This means everything on the previous CAR stack will need to migrate to the new stack below 'stack_top'. This includes global data, early malloc pointers, arch_cpu_init() stack variables and its return address. 2). Copy previous global_data to the new places under stack_top, and fix up gd->arch.gd_addr. 3). The initf_malloc() is called before arch_cpu_init() so we need fix up the early malloc pointers manually (gd->malloc_base and gd->malloc_limit) 4). Fix up the stack variables and return address of arch_cpu_init() on the new stack. 5). On Tunnel Creek, if we call setup_gdt() in start.S, later fsp_init() in arch_cpu_init() will fail to bring up the thread 1 (Tunnel Creek supports SMT), the reason of which is unknown to me yet (FSP is a black box). It looks to me that FSP is assuming GDT only contains two entries (32-bit 4G flat address) before calling fsp_init().
I have not looked into this any further, so the above points might not be 100% right. I would say with these modifications, the codes are more difficult to understand.
Regards, Bin