Finally we have succeeded in forcing coreboot to enable AMD discrete GPU of Lenovo G505S and load its' AtomBIOS ROM there :-) (see P.S.) But that's not enough - seems that a correct PCI config is needed! Otherwise, without a nomodeset option there is a strange kernel panic at the very beginning of booting, and with nomodeset this dGPU is simply disabled at Linux - later modprobe'ing a driver doesn't work.
We will appreciate if you could take a quick glance and tell what PCI config space bits are wrong there, and we will try a hack of multiple config space writes according to your ideas
coreinfo_pci_with_0_02_00_enabled - extracted with coreinfo before trying to boot Linux
1) Bridge (enabled)
.C. 00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F 00: 22 10 12 14 07 00 10 00 00 00 04 06 10 00 01 00 10: 00 00 00 00 00 00 00 00 00 01 01 00 11 11 00 00 20: 00 F0 00 F0 01 E0 F1 EF 00 00 00 00 00 00 00 00 30: 00 00 00 00 50 00 00 00 00 00 00 00 00 01 03 00 40: all 00's 50: 01 58 03 C8 00 00 00 00 10 A0 42 01 21 80 00 00 60: 30 28 00 00 02 0D 70 00 00 00 82 B0 00 00 04 00 70: 00 00 48 01 00 00 01 00 00 00 00 00 1F 00 70 00 80: 06 80 00 00 06 00 00 00 02 00 00 00 00 00 00 00 90: all 00's A0: 05 B0 80 00 00 00 00 00 00 00 00 00 00 00 00 00 B0: 0D B8 00 00 22 10 34 12 08 00 03 A8 00 00 00 00 C0-D0: all 00's E0: 50 00 00 00 10 00 00 00 00 00 00 00 00 00 00 00 F0: all 00's
2) Discrete GPU (R5 M230) behind the bridge
.F. 00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F 00: 02 10 65 66 03 00 10 00 00 00 80 03 10 00 00 00 10: 0C 00 00 E0 00 00 00 00 04 00 00 F0 00 00 00 00 20: 01 10 00 00 00 00 00 00 00 00 00 00 00 00 00 00 30: 00 00 04 F0 48 00 00 00 00 00 00 00 00 01 00 00 40: 00 00 00 00 00 00 00 00 09 50 08 00 00 00 00 00 50: 01 58 03 76 00 00 00 00 10 A0 12 00 A1 8F 00 00 60: 30 28 00 00 82 0C 40 00 00 00 82 10 00 00 00 00 70: all 00's 80: 00 00 00 00 0E 00 00 00 02 00 00 00 00 00 00 00 90: all 00's A0: 05 00 80 00 00 00 00 00 00 00 00 00 00 00 00 00 B0-F0: all 00's
If more info is needed, all the PCI config spaces and their differences are highlighted at this "hybrid PDF" (editable with LibreOffice Writer), view it in your web browser here - https://github.com/mikebdp2/coreboot-related/blob/master/PCI.pdf - also attached to an e-mail. There are the pages like "dont_enable_bridge_and_let_it_configure_in_linux : normalmode vs nomodeset", "coreinfo_PCI_with_0_02_00_enabled" and also the PCI config spaces of proprietary UEFI normalmode - discrete GPU is working there! - as well as UEFI nomodeset (to get an understanding what normalmode vs nomodeset differences are acceptable and maybe try to apply this logic to coreboot's situation to understand how a coreboot's normalmode could have looked if no kernel panic) . UEFI config space can't be copied blindly because e.g. a different ROM address is OK and should be preserved , but some bits could be borrowed to ensure a correct configuration.
P.S. 1) discrete GPU = PCI device 01:00.0 / 04:00.0 with VID,PID=1002,6665 (for R5 M230) - or ,6663 (for HD 8570M) - is behind a PCI bridge 00:02.0 with VID,PID=1022,1412 . At coreboot/src/mainboard/lenovo/g505s/devicetree.cb there is a line 32 : device pci 2.0 off end ===> Change it to device pci 2.0 on end 2) at ./coreboot/src/device/pci_device.c --> pci_dev_init, lines 784-787:
/* Only execute VGA ROMs. */ if (((dev->class >> 8) != PCI_CLASS_DISPLAY_VGA)) return;
PCI device classes are declared at ./coreboot/src/include/device/pci_ids.h , e.g. lines 31-35 :
#define PCI_BASE_CLASS_DISPLAY 0x03 #define PCI_CLASS_DISPLAY_VGA 0x0300 #define PCI_CLASS_DISPLAY_XGA 0x0301 #define PCI_CLASS_DISPLAY_3D 0x0302 #define PCI_CLASS_DISPLAY_OTHER 0x0380
Inserted printk's told us that dev->class for dGPU is 28672 = 0x38000 , right shift by 8 bits : ( 0x38000 >> 8 ) = 0x0380 - this is PCI_CLASS_DISPLAY_OTHER . Expanded the code above to
/* Only execute VGA ROMs. */ if ((((dev->class >> 8) != PCI_CLASS_DISPLAY_VGA))&&(((dev->class
- != PCI_CLASS_DISPLAY_OTHER))) {
printk(BIOS_DEBUG, "((dev->class >> 8) != PCI_CLASS_DISPLAY_VGA), PCI_CLASS_DISPLAY_OTHER also\n"); return; }
and now it loads the AtomBIOS ROM on a discrete GPU also (but a correct PCI config is still needed to get it working, please see above)
Best regards, Mike Banon
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Mike Banon