lspci: what do Revision Number and PCI Class mean?

Question

I have a notebook Lenovo IdeaPad G500A (59-381065). OS: openSUSE 13.1. My video cards are Intel HD Graphics 4000 and AMD Radeon HD 8750M;

#  lspci | grep 'VGA\|ATI'
00:02.0 VGA compatible controller: Intel Corporation 3rd Gen Core processor Graphics Controller (rev 09)
01:00.0 Display controller: Advanced Micro Devices, Inc. [AMD/ATI] Mars [Radeon HD 8670A/8670M/8750M]

My friend has similar notebook (under Ubuntu 14.04 LTS) with the same dedicated card, but result of this command contains the revision number (rev ff) for it:

# lspci | grep 'VGA\|ATI' 
00:02.0 VGA compatible controller: Intel Corporation 4th Gen Core Processor Integrated Graphics Controller (rev 06)
01:00.0 Display controller: Advanced Micro Devices, Inc. [AMD/ATI] Mars [Radeon HD 8670A/8670M/8750M] (rev ff)

In forums.amd.com/Support of HD 8750M and linux drivers 14.501.1003 or beta user has the same AMD card in the HP machine, but it is detected as VGA-compatible device:

lspci | grep VGA
00:02.0 VGA compatible controller: Intel Corporation 3rd Gen Core processor Graphics Controller (rev 09)
01:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] Mars [Radeon HD 8670A/8670M/8750M] (rev ff)

Could somebody explain

1. what is revision number and what do its particular values and its absence mean?
2. what difference between "VGA compatible" and "display" controllers and why the same card has different PCI classes in different machines?

Or could somebody please give a link, where I can read about this?

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P.S.

Actually, this issue has arisen from attempts to run the dedicated card with proprietary driver. The final target of this is OpenCL programming.

On the first two listed machines we haven't achieve any success. All versions of AMD driver which support 8750M card were tried with different versions of Intel driver. Various distributions of Linux of various versions were tried too.

In all cases driver is installed, but after reboot X don't start with error

(EE) fglrx(0): Failed to open CMMQS connection.

The discussion of this general issue can be found in forums.amd.com/Intel HD 4000 + AMD Radeon HD 8750M + Linux.

Further experiments require deeper understanding, how does it work.

So, thank you in advance for any help.

Regards, Natalia

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Seems, I have found the revision number of my discrete GPU in /var/log/Xorg.0.log:

[    23.516] (--) PCI:*(0:0:2:0) 8086:0166:17aa:3800 rev 9, Mem @ 0xd8000000/4194304, 0xc0000000/268435456, I/O @ 0x00004000/64
[    23.516] (--) PCI: (0:1:0:0) 1002:6600:17aa:3800 rev 0, Mem @ 0xd0000000/134217728, 0xd8600000/262144, I/O @ 0x00003000/256, BIOS @ 0x????????/131072

so, it equals 0. But what does it mean?.. What difference between (rev 9) and (rev 0), for example? And this doesn't solve above mentioned issues...