On 7/5/23 15:06, Bjorn Helgaas wrote:
On Wed, Jun 28, 2023 at 01:09:49PM +0800, Kai-Heng Feng wrote:
On Wed, Jun 28, 2023 at 4:54 AM Bjorn Helgaas <helgaas@xxxxxxxxxx> wrote:
On Tue, Jun 27, 2023 at 04:35:25PM +0800, Kai-Heng Feng wrote:
On Fri, Jun 23, 2023 at 7:06 AM Bjorn Helgaas <helgaas@xxxxxxxxxx> wrote:
On Tue, Jun 20, 2023 at 01:36:59PM -0500, Limonciello, Mario wrote:
It's perfectly fine for the IP to support PCI features that are not
and can not be enabled in a system design. But I expect that
strapping or firmware would disable those features so they are not
advertised in config space.
If BIOS leaves features disabled because they cannot work, but at the
same time leaves them advertised in config space, I'd say that's a
BIOS defect. In that case, we should have a DMI quirk or something to
work around the defect.
That means most if not all BIOS are defected.
BIOS vendors and ODM never bothered (and probably will not) to change
the capabilities advertised by config space because "it already works
under Windows".
This is what seems strange to me. Are you saying that Windows never
enables these power-saving features? Or that Windows includes quirks
for all these broken BIOSes? Neither idea seems very convincing.
I see your point. I was looking through Microsoft documentation for
hints and came across this:
https://learn.microsoft.com/en-us/windows-hardware/customize/power-settings/pci-express-settings-link-state-power-management
They have a policy knob to globally set L0 or L1 for PCIe links.
They don't explicitly say it, but surely it's based on what the devices
advertise in the capabilities registers.
So the logic is to ignore the capability and trust the default set
by BIOS.
I think limiting ASPM support to whatever BIOS configured at boot-time
is problematic. I don't think we can assume that all platforms have
firmware that configures ASPM as aggressively as possible, and
obviously firmware won't configure hot-added devices at all (in
general; I know ACPI _HPX can do some of that).
Totally agree. I was not suggesting to limiting the setting at all.
A boot-time parameter to flip ASPM setting is very useful. If none has
been set, default to BIOS setting.
A boot-time parameter for debugging and workarounds is fine. IMO,
needing a boot-time parameter in the course of normal operation is
not OK.
Bjorn
