[coreboot] TXE and Descriptor bin management in Coreboot

Zoran Stojsavljevic zoran.stojsavljevic at gmail.com
Fri Jul 15 07:06:27 CEST 2016


Hello Brett,

Having overall experience with INTEL, I should say that the Truth is a bit
more complicated. ;-)

In the simplified view, there are two points when bringing any INTEL CPU
from reset, i should say. The first is: HW strap conditions, and these need
to be set appropriately, depending upon what the HW config will be. This
point I mentioned since I am not sure if XDP port only depends upon TXE, I
do not really know with certainty for BYT, but I do know for some other
families HW straps also need to be set properly for XDP to be enabled.
Maybe there are two requirements for XDP to be enabled, so I am really not
sure about this, this is why I am writing this email.

So, the question I have here is: does BYT have to have one of the HW straps
properly set (maybe it is already set by default design) for XDP to be
enabled?

The another point why TXE HW/FW engine is mainly used is the following:  TXE
Firmware, the Trusted eXecution Engine, provide features to prevent BIOS
tampering, however information about TXE is considered Intel Confidential
and require that you have CNDA account.

Usually, FSP + Coreboot (as you have mention already), is built on the top
of normal BIOS (last 2M, maybe these days 3M, since FSP and Coreboot are
growing) , since normal BIOS includes SW straps (second point), which are
also set by default (in BIOS). In this scenario, FIT (formerly FITC) tool
is not required (if satisfied with default SW straps, which 99% developers
are).

Here is INTEL site where there are overall set of BYT documents, but many
of them are locked (as well as 514482):

[image: Inline image 1]

http://www.intel.com/content/www/us/en/embedded/products/bay-trail/software-and-drivers.html

Hope this helps also,

Zoran



On Thu, Jul 14, 2016 at 9:51 PM, Testerman, Brett (US COM) <
Brett.Testerman at cobham.com> wrote:

> Mayuri,
>
>
>
> Your best bet with all of this is to contact Intel and get a privileged
> access account. If that is not possible or practical then you need to do
> some reverse engineering.
>
>
>
> First of all, go get this document from Intel’s web site:
>
>
>
> 514482_ByTti_SoC_SPIFlashProgGuide_Rev1p0.pdf
>
>
>
> I don’t have a specific link to it but I know it is publically accessible.
> Search on the leading 6 digit number or “SPI Flash Programming Guide”. This
> document fully describes the descriptor tables and how to use them. The
> FITC tool is the preferred way but you can bit-bang them with the info
> provided in that doc.
>
>
>
> As for the TXE you will need to get that from Intel – it is not publically
> available. But I can say if you are running on the E3800 family (Bay Trail)
> then you don’t need it. The chip will boot without it but the XDP port will
> be locked out. You can also use the information from the programming guide
> to locate a TXE image in a 3rd party boot image and extract it out of
> that. I think that is what the idftool does.
>
>
>
> The coreboot image will need to be located at the very end of flash
> because that is where the hardware reset vector is. The nice thing about
> that is once you have set up the descriptors you don’t have to
> rebuild/reprogram the entire flash image every time. For example, if your
> coreboot image is only 1MB in size then you only need to reprogram the last
> 1 megabyte of flash and leave the rest alone. Saves a ton of time.
>
>
>
> There has been a lot of talk about this issue on Intel’s embedded
> communities forums. Check out this thread:
>
> https://embedded.communities.intel.com/thread/12354
>
>
>
> Hope this helps!
>
>
>
> Brett
>
>
>
>
>
>
>
> *From:* coreboot [mailto:coreboot-bounces at coreboot.org] *On Behalf Of *Stefan
> Reinauer
> *Sent:* Wednesday, July 13, 2016 4:30 PM
> *To:* Mayuri Tendulkar
> *Cc:* Martin Roth; coreboot
> *Subject:* Re: [coreboot] TXE and Descriptor bin management in Coreboot
>
>
>
> *** Please note that the Sender of this email is from outside the Cobham
> NA IT Hub ** *
>
> * Mayuri Tendulkar <mayuri.tendulkar at aricent.com> [160714 00:50]:
> > Ok, so do we need to ask Intel if we use Intel baytrail processor? How
> we can create this descriptor.bin?
>
> Please have a look at util/ifdtool and util/ifdfake for our tools
> dealing with Intel Firmware Descriptors. The most comprehensive way of
> producing the information you need is by using Intel's fitc tool,
> however.
>
> If you are willing to put some development effort into this, we could
> use help, merging ifdtool and ifdfake, as well as incorporating more
> fitc like capabilities into the tool.
>
> Stefan
>
>
>
> --
> coreboot mailing list: coreboot at coreboot.org
> https://www.coreboot.org/mailman/listinfo/coreboot
>
> --
> coreboot mailing list: coreboot at coreboot.org
> https://www.coreboot.org/mailman/listinfo/coreboot
>
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