(2010/07/30 0:45), Rafael J. Wysocki wrote:
On Thursday, July 29, 2010, Kenji Kaneshige wrote:
(2010/07/29 6:43), Jesse Barnes wrote:
On Wed, 28 Jul 2010 23:23:56 +0200
"Rafael J. Wysocki"<rjw@xxxxxxx> wrote:
From: Rafael J. Wysocki<rjw@xxxxxxx>
PCIe port service drivers ask the BIOS, through _OSC, for control of
the services they handle. Unfortunately, each of them individually
asks for control of the PCIe capability structure and if that is
granted, some BIOSes expect that the other PCIe port services will be
configured and handled by the kernel as well. If that is not the
case (eg. one of the PCIe port service drivers is not loaded), the
BIOS may be confused and may cause the system as a whole to misbehave
(eg. on one of such systems enabling the native PCIe PME service
without loading the native PCIe hot-plug service driver causes a
storm of ACPI notify requests to appear).
For this reason rework the PCIe port driver so that (1) it checks
which native PCIe port services can be enabled, according to the
BIOS, and (2) it requests control of all these services
simultaneously. In particular, this causes pcie_portdrv_probe() to
fail if the BIOS refuses to grant control of the PCIe capability
structure, which means that no native PCIe port services can be
enabled for the PCIe root complex the given port belongs to.
Make it possible to override this behavior using a new command line
switch pcie_ports= that can be set to 'auto' (ask the BIOS, the
default), 'native' (use the PCIe native services regardless of the
BIOS response to the control request), or 'compat' (do not use the
PCIe native services at all).
Accordingly, rework the existing PCIe port service drivers so that
they don't request control of the services directly.
Signed-off-by: Rafael J. Wysocki<rjw@xxxxxxx>
---
Kenji-san, are you ok with this version? I would like to get your ack
(and ideally your tested-by) for this one since it affects
functionality you need.
Hi Jesse, Rafael,
I've just started reviewing the latest version of the patch. I have good
impression about this version so far. Please give me a few days for deeper
review. And I've booked the test machine for this patch in next week. I'll
try to test the patch and send you the result as soon as I can.
Here are two comments I have so far.
Though it is not directly related to Rafael's patch, I found one problem
in _OSC query handling while reviewing this patch. Currently, all the
_OSC controls are queried at the same time in acpi_pci_osc_support() and
the result is preserved for later acpi_pci_osc_control_set() call. But
query result can vary depending on the combination of requested controls.
In principle it can, but acpi_pci_query_osc() asks for all aplicable control
bits, in which case the formware can only clear those bits in the response if
the corresponding features are unsupported. Doing otherwise would be in
violation of Section 6.2.9.1. of ACPI spec 3.0b, the following in particular:
"If any bits in the Control Field are returned cleared (masked to zero) by the _OSC control method,
the respective feature is designated unsupported by the platform and must not be enabled by the OS."
My concern is as follows.
For easy, assume as follows:
- all the _OSC controls are A, B, C
-B depends on C.
- When requesting A, B and C, all A, B and C are granted to OS.
- When requesting A, B, only A is granted to OS.
Current linux queries all A, B and C at the boot time and preserve the
result (all A, B and C can be granted to OS). Here, if a service driver
requests A and B using acpi_pci_osc_control_set(), acpi_pci_osc_control_set()
checks if both of those controls can be granted to OS. The expected result
here is only A can be granted to OS, but current linux judges both of them
can be granted because linux does this check by seeing preserved result.
As a result, acpi_pci_osc_control_set() evaluates _OSC with query flag
cleared to request A and B. Since the control B returned cleared,
acpi_pci_osc_control() returns error to the service driver. As a result,
control A is granted to OS even though there is no driver to handle the
control A.
So I think query result must not be preserved. Since Rafael's patch uses
query result, this problem should be fixed at the same time. I'll try to
make a patch for this and update Rafael's patch if needed.
It would be sufficient to change acpi_pci_osc_control_get(), introduced
by my patch, to call acpi_pci_query_osc() unconditionally, but as I said above,
I don't think it's necessary.
I made a patch for this and updated your patch slightly. I'll send them soon.
I think the following changes should be done in the separated patch. I
guess this change is for the BIOS which enables hotplug interrupt at when
_OSC is evaluated with native hot-plug control. Right?
Yes, it is.
Anyway, it should be separated patch with appropriate description.
But the $subject patch does analogous things for AER and PCIe PME. Do you
think they also should be introduced by separate patches?
I think the following changes in your patch should be introduced by
separate patches.
- optimizing the checks in acpi_pci_osc_control_set()
- Disabling hot-plug interrupt
- Removing module_exit()
Thanks,
Kenji Kaneshige
--
To unsubscribe from this list: send the line "unsubscribe linux-pci" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
