Hi all,
I think I've noticed a general linux-BIOS problem: Some PCI devices are not being enabled for bus mastery! Let me more clearly explain the context:
1) According to my handy PCI book: All bus master capable PCI devices must implement bit 2 of the command register. 2) Most devices that implement this bit power up default to 1. This is good, because linuxbios has not been setting this bit to 1. 3) A user reported a problem with a 802.11b card, and upon investigation I discovered the chip used on this card does not default to a 1 for bus master enable. (See attached lspci output)
After some testing, I realized that the same card on a non LinuxBIOS based machine works correctly - i.e. by the time the kernel is up I see that this bus master enable bit is 1. I know that the Award BIOS on this second machine must have set this bus master enable bit - because the kernel and drivers are identical. I verified this by dumping the appropriate config registers early on in kernel start-up.
My theory is that the Award BIOS is doing something that we are not: During the IO/Mem space assignment process it is setting the bus master bit for most devices. By "most devices" I mean any device that is not behind a bridge that inhibits bus mastery. My PCI Sys Arch book (by Shanley and Anderson) says that some crummy bridges may not support bus mastery (i.e. they have a bit 2 of the command register that always reads as zero). If a device is behind a bridge that does not support mastery, it must have its mastery bit cleared.
Does anyone have a copy of the $$$ PCI architecture spec so they can check this? My PCI System Architecture book is vague on the topic.
My proposed fix:
* Add pci_enable_bus_masters() that does the following: * Calls pci_enable_bus_master(0) to enable devices directly connected to the host bridge
* Add pci_enable_bus_master(devfn) that does the following: * Try to enable bus mastery for this device. * If the device is a bridge: * If the write of master enable fails, then write zero to all "bus master enable" bits for devices behind that bridge (including all subordinate buses) * If the write of master enable succeeds, then call pci_enable_bus_master for all devices on the secondary bus behind this bridge. (i.e. not for all subordinate busses)
I've added these functions and called them after the standard linuxbios PCI setup. The problem card now works as well as it did with Award BIOS. What to ya'll think? I'm particularly interested in quotes from the PCI architecture spec.
Kevin
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On a linux BIOS machine:
00:14.0 Network controller: Harris Semiconductor: Unknown device 3873 (rev 01) Subsystem: D-Link System Inc: Unknown device 3501 Flags: medium devsel, IRQ 5 Memory at feb00000 (32-bit, prefetchable) [size=4K] Capabilities: [dc] Power Management version 2 00: 60 12 73 38 02 00 90 02 01 00 80 02 08 40 00 00 10: 08 00 b0 fe 00 00 00 00 00 00 00 00 00 00 00 00 20: 00 00 00 00 00 00 00 00 00 00 00 00 86 11 01 35 30: 00 00 00 00 dc 00 00 00 00 00 00 00 05 01 00 00 40: 80 80 00 00 00 00 00 00 00 00 00 00 00 00 00 00 50: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 60: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 70: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 90: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 a0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 b0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 c0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 d0: 00 00 00 00 00 00 00 00 00 00 00 00 01 00 02 7e e0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 f0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
On a non linux BIOS machine:
00:0a.0 Network controller: Harris Semiconductor: Unknown device 3873 (rev 01) Subsystem: D-Link System Inc: Unknown device 3501 Flags: bus master, medium devsel, latency 32, IRQ 10 Memory at ee000000 (32-bit, prefetchable) [size=4K] Capabilities: [dc] Power Management version 2 00: 60 12 73 38 07 00 90 02 01 00 80 02 08 20 00 00 10: 08 00 00 ee 00 00 00 00 00 00 00 00 00 00 00 00 20: 00 00 00 00 00 00 00 00 00 00 00 00 86 11 01 35 30: 00 00 00 00 dc 00 00 00 00 00 00 00 0a 01 00 00 40: 80 80 00 00 00 00 00 00 00 00 00 00 00 00 00 00 50: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 60: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 70: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 90: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 a0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 b0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 c0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 d0: 00 00 00 00 00 00 00 00 00 00 00 00 01 00 02 7e e0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 f0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00