iMC Configuration Registers reads all 1 (ffffffff)

[Xingbo_W_]

The machine is a Dell R630 Server with two Xeon E5-2680 v3. When I'm trying to access the memory Controller registers (7f:14.0 or 7f:14.1) with setpci, it always reads ffffffff. I tried to write the the registers but it says "pcilib: sysfs_write: write failed: File too large".

As shown on the corresponding datasheet vol2, If I access the standard PCIe registers such as DID,VID, I can get valid values.

# setpci -s 7f:14.0 0.l
2fb08086

# setpci -s 7f:14.0 4.l
00100000

# setpci -s 7f:14.0 8.l
08800002

# setpci -s 7f:14.0 c.l
00800000

# setpci -s 7f:14.0 2c.l
2fb08086

# setpci -s 7f:14.0 3c.l
00000000

# setpci -s 7f:14.0 40.l
00910010

# setpci -s 7f:14.0 108.l
ffffffff

and all ffffffff for the rest of the registers.

[McCalpinJohn]

I don't think that the "extended PCI Configuration Space" is intended to be visible here.

Volume 2 of the Xeon E5 v3 data sheet warns that this is the case for devices 0x13 (19d) and 0x16 (22d), but it appears to be the case for the other integrated Memory Controller PCI configuration space devices as well.

[Xingbo_W_]

John McCalpin wrote:

I don't think that the "extended PCI Configuration Space" is intended to be visible here.

Volume 2 of the Xeon E5 v3 data sheet warns that this is the case for devices 0x13 (19d) and 0x16 (22d), but it appears to be the case for the other integrated Memory Controller PCI configuration space devices as well.

Looks like that. There is no resource0..resourceN in the corresponding sysfs' directory.

[Wei_C_]

hi McCalpin,

I also have similar issues for accessing 7f:14.0 for memory bandwidth throttling. However, based on the datasheet, it say I may need to configure chn_temp_cfg whose offset is 0x108 but unseen for me. So, I am wondering if you have any ideas to help me solve this problem?

Best

Wei

[McCalpinJohn]

Unfortunately you will need a special BIOS to access the extended PCI configuration space that is "hidden".   For read-only access, it might be possible to convince a vendor to provide a BIOS-level interface to dump these bits.  Few of these configuration bits are safe to modify on a "live" system.