Re: [PATCH V8 0/4] PCI: vmd: Enable PCIe ASPM and LTR on select hardware

[David E. Box]

Hi You-Sheng,

On Wed, 2022-11-23 at 18:27 +0800, You-Sheng Yang wrote:
> Hi David,
> 
> On 11/3/22 10:18, David E. Box wrote:
> > This series adds a work around for enabling PCIe ASPM and for setting PCIe
> > LTR values on VMD reserved root ports on select platforms. While
> > configuration of these capabilities is usually done by BIOS, on these
> > platforms these capabilities will not be configured because the ports are
> > not visible to BIOS. This was part of an initial design that expected the
> > driver to completely handle the ports, including power management. However
> > on Linux those ports are still managed by the PCIe core, which has the
> > expectation that they adhere to device standards including BIOS
> > configuration, leading to this problem.
> > 
> > The target platforms are Tiger Lake, Alder Lake, and Raptor Lake though the
> > latter has already implemented support for configuring the LTR values.
> > Meteor Lake is expected add BIOS ASPM support, eliminating the future need
> > for this work around.
> 
> 
> It appears to me that this patch series works only on Tiger Lake. We 
> have tried to revert our current work-arounds in Ubuntu kernels 
> generic-5.15/oem-5.17/oem-6.0/unstable-6.1 and apply this series, the 
> prebuilt kernels can be found in:
> 
>    https://launchpad.net/~vicamo/+archive/ubuntu/ppa-1996620
> 
> However, only TGL can still enter PC10 as before.
> 
> 
> ADL-M, RPL platforms will stay in PC3 with vmd LTR set, but ASPM 
> disabled.

For the patch to work BIOS must allow the OS to control ASPM. If this is not the
case then you will see the message "ACPI FADT declares the system doesn't
support PCIe ASPM, so disable it". Please check for this on the systems that
don't work. If so the only option is a BIOS change to enable it.

David

>  i915 RC6 blocked, too:
> 
> $ sudo cat /sys/kernel/debug/dri/
> 
> 0/i915_dmc_info
> ...
> DC3CO count: 0
> DC3 -> DC5 count: 100
> DC5 -> DC6 count: 0
> 
> 
> > Note, the driver programs the LTRs because BIOS would also normally do this
> > for devices that do not set them by default. Without this, SoC power
> > management would be blocked on those platform. This SoC specific value is
> > the maximum latency required to allow the SoC to enter the deepest power
> > state.
> > 
> > This patch addresses the following open bugzillas on VMD enabled laptops
> > that cannot enter low power states.
> > 
> > Link: https://bugzilla.kernel.org/show_bug.cgi?id=212355
> > Link: https://bugzilla.kernel.org/show_bug.cgi?id=215063
> > Link: https://bugzilla.kernel.org/show_bug.cgi?id=213717
> > 
> > David E. Box (3):
> >    PCI: vmd: Use PCI_VDEVICE in device list
> >    PCI: vmd: Create feature grouping for client products
> >    PCI: vmd: Add quirk to configure PCIe ASPM and LTR
> > 
> > Michael Bottini (1):
> >    PCI/ASPM: Add pci_enable_link_state()
> > 
> >   drivers/pci/controller/vmd.c | 96 ++++++++++++++++++++++++++----------
> >   drivers/pci/pcie/aspm.c      | 54 ++++++++++++++++++++
> >   include/linux/pci.h          |  7 +++
> >   3 files changed, 131 insertions(+), 26 deletions(-)
> > 
> > 
> > base-commit: 247f34f7b80357943234f93f247a1ae6b6c3a740
> 
> 
> Regards,
> You-Sheng Yang
>