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
---
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