Mpfff, there aren't many replies; seems I didn't satisfy what you want
to have...
At first I want to mention that I just want to help the Debian project
and started testing Debian Wheezy my old ia64 box.
Since these are my first messages on the kernel lists, I really don't
feel me in a position to tell you what's right or wrong for the Kernel
- I guess you have much more Linux Kernel knowledge than me.
The firmware left the memory BAR at 0x24 cleared (0x00000000), but it
also left the MEM bit in the command register disabled. So it seems
like a Linux bug that we're trying to use that zero address from the
BAR. If the firmware left the MEM or IO decode enable bit cleared,
why would we assume it put anything useful in the corresponding BARs?
Your idea would be a fundamental change in the Kernel; I just want to
fix the ata_piix problem in Debian Wheezy.
I can't tell you whether the developer of the EFI thought this. Maybe
it is simply a bug.
If you would evaluate the command registers, which the BIOS or EFI has
initialized, you would work around some wrong BARs. You might run into
trouble due to wrong command register values instead.
Are you sure that any BIOS or EFI sets the command registers correctly?
Currently the Linux Kernel sets and clears the IORESOURCE_MEM and
IORESOURCE_IO bits in the command registers as needed.
Windows reconfigures any PCI device. The settings of the BIOS or EFI
do not matter at all; the user doesn't experience any BIOS bug at all.
This still isn't very generic. It only looks at BAR 5 and only for
IDE controllers, so it fixes the problem for this device and this
BIOS, but there's no reason the same problem couldn't happen on other
devices and other BARs.
My proposal was basically:
pci_read_config_word(dev, PCI_COMMAND, &cmd);
for (i = 0; i < 6; i++) {
/* read BAR i here */
r = dev->resource[i];
if (((r->flags & IORESOURCE_MEM) && (cmd & PCI_COMMAND_MEMORY)) ||
((r->flags & IORESOURCE_IO) && (cmd & PCI_COMMAND_IO))) {
/* treat resource as valid */
} else {
/* treat resource as unassigned; try to assign it later */
}
}
Both of my two patches hide the BAR5 when we know that BAR5 is not functional.
The first patch makes sure that the PCI device id matches; the second
one checks whether it is an ide controller in legacy mode. The
associated ide/piix or ata/ata_piix doesn't need the BAR5 memory
resource at all.
The other BARs are functional and needed.
I don't know what regression can occur when you hide *any*
uninitialized BAR of *any* pci device. Some drivers might be screwed
up when a needed mem resource is absend - after pci_enable_device() or
pcim_enable_device() returned success.
Ben Hutchings of the Debian project pointed to some interesting detail
about ide/piix:
"By the way, the reason the old IDE driver worked is that
drivers/ide/setup-pci.c has a fallback for this:
if (pci_enable_device(dev)) {
ret = pci_enable_device_io(dev);
It was added almost exactly 10 years ago without any specific comment."
Debian had both ide/piix and ata/ata_piix in the past. When ata_piix
didn't initialize, ide/piix took over the device. The user didn't
experience any problem.
The old ide/piix has been removed with recent Debian versions (due to
problems with shared interrupts). Thus, the ICH4 problem is on the
table again.
Since you don't want to take my patches, I need some new ideas. The
patch shouldn't be a fundamental, experimental change with the risk of
regression because it is intended for a *stable* Debian release.
Suggestions or comments are appreciated.
Stephan
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