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Re: [Qemu-devel] [PATCH v2] arm: add device tree support


From: Anthony Liguori
Subject: Re: [Qemu-devel] [PATCH v2] arm: add device tree support
Date: Wed, 01 Feb 2012 07:44:27 -0600
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.23) Gecko/20110922 Lightning/1.0b2 Thunderbird/3.1.15

On 02/01/2012 07:32 AM, Alexander Graf wrote:

On 01.02.2012, at 14:25, Anthony Liguori wrote:

On 02/01/2012 07:10 AM, Peter Maydell wrote:
On 1 February 2012 13:04, Anthony Liguori<address@hidden>   wrote:
How does it race?  Devices normally never touch memory so a loader device
will be the only thing mucking with memory.

The obvious one is "loader reset function wants to set starting PC to
entry point of kernel/etc" vs "CPU device reset wants to set starting
PC to hardware-mandated reset vector". We have this at the moment, of
course, and I think we implicitly rely on reset handlers being called
in order of registration...

I'm a bit confused, why can't the kernel loader be implemented in terms of a 
firmware blob?

This is what we do for x86 and it solves this problem robustly.  Isn't it just 
a matter of a few instructions to do a jmp to a known location?

Only if you have non-semi-hosted modes. For e500 for example, we don't have a bios flash 
region mapped through mmio available. So we would have to write the "jump to 
kernel" code into ram. But where in RAM? Linux starts at address 0, so that one's 
taken.

The processor has to have a defined sequence where IP is fixed to a specific value, no?

How else would the real hardware bootstrap software?

Regards,

Anthony Liguori


Alex






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