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) <t...@linaro.org> 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...
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