Sorry for exhuming this post. I have an x9dre-ln4f I have been working on enabling bifurcation and this thread has been great.
My bios (latest v3.3) has the IIO bifurcation sections but the settings are statically set to what supermicro deemed they needed, a mixture of x8, x8x8, and x16. When I extract the data and parse with IFR, only the existing options exist, there are no options for the other combinations (i.e. x4x4x4x4)
I have not use RU to change the value yet, the feeling I get from others who have tried similar on different boards is that it didn’t work. I started to go down the path of reading the intel register specifications and came across your thread.
I can use setpci to read the values for pcie_iou_bif_ctrl in the pci config and those values match what i see in the bios and the specification. However, I noticed in the spec at bit 3 there is a ‘bifurcation enable’ bit that needs set to 1 in addition to bits 3:0 to set the channels. I wonder if when people have tested modifying the bios settings in situations like mine where bifurcation is not fully supported in the bios if this bit is not getting set to 1. I also can’t tell if its being set to 1, the spec states it always read 0b - https://www.intel.com/content/dam/www/public/us/en/documents/datasheets/xeon-e5-v2-datasheet-vol-2.pdf pg.235
If I may ask,
Have you ever attempted to write to this register directly?
Do you know how to see what registers/bits the bios is setting based on the selected bios options?
any input welcome!
Thanks,