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

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Date:   Fri, 25 Nov 2022 00:39:58 +0800
From:   You-Sheng Yang <vicamo.yang@...onical.com>
To:     david.e.box@...ux.intel.com
Cc:     michael.a.bottini@...el.com, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org, me@...ityamohan.in,
        rafael@...nel.org, hch@...radead.org, robh@...nel.org,
        bhelgaas@...gle.com, kw@...ux.com, lorenzo.pieralisi@....com,
        nirmal.patel@...ux.intel.com, jonathan.derrick@...ux.dev
Subject: Re: [PATCH V8 0/4] PCI: vmd: Enable PCIe ASPM and LTR on select hardware

On Thu, Nov 24, 2022 at 12:09 AM David E. Box
<david.e.box@...ux.intel.com> wrote:
>
> 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.

Thank you. It's exactly what you said. The ADL-M/RPL platforms I have
do not support OS PCIe ASPM.

> 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
> >
>


-- 
Regards,
You-Sheng Yang