[coreboot] Boots from PCI add-on card on Intel ICHs
oliverlist at schinagl.nl
Sat Jun 9 18:13:40 CEST 2012
Having been quite intrigued by this I coincidentally found an old raid
controller of mine.
Though it only has 64kb flash I'm guessing (the bios image is about 55k)
after a swap of that chip, it may theoretically be possible, correct?
So why would this only work on ICH based boards? What are changes of
this working on older chipsets other then intel? Say VIA?
On 26-05-12 10:15, Kyösti Mälkki wrote:
> On Sun, 2012-05-20 at 11:23 +0300, Kyösti Mälkki wrote:
>> I did not find this method of bypassing the mainboard flash chip and
>> booting from PCI add-on card documented or discussed before. The nice
>> think in this is that neither mainboard or its flash needs to be
>> modified. Good news in the case of a soldered flash and this method may
>> work with mini-PCI slots on laptops too.
>> For pre-ICH6 the key is in subtractive PCI decode. This has been
>> supported in 82801 chipset from the early days and is briefly documented
>> in ICH3 datasheet , see 5.1.1. PCI Bus interface. This decode mode is
>> on by default and there is no documentation of a hw bootstrap that could
>> disable it.
> Above is not accurate, ICH6 has hardware bootstrap.
>> For ICH7 onwards there are HW bootstraps to select between LPC/SPI/PCI.
>> If you don't know where the bootstraps are, go with SPI and forget about
>> this PCI add-on boot.
> The bootstrap is latched on power cycle, but not PCI reset, and the
> config bit is writeable. So if one has a booting system it should be
> possible to switch to PCI add-on for next reboot. The setting will
> default back to mainboard flash after power-cycle.
> Note that "hard/cold" reboot is required to toggle the PCI RST#. If
> vendor BIOS does set the write-protection lock bit, it should be cleared
> on PCI RST#. At least for ICH4 that is the case.
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