linux-kernel - Re: [PATCH V10 0/4] Enable PCIe ASPM and LTR on select hardware

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Date:   Thu, 19 Jan 2023 21:28:45 -0800
From:   Sathyanarayanan Kuppuswamy 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
To:     "David E. Box" <david.e.box@...ux.intel.com>,
        nirmal.patel@...ux.intel.com, jonathan.derrick@...ux.dev,
        lorenzo.pieralisi@....com, hch@...radead.org, kw@...ux.com,
        robh@...nel.org, bhelgaas@...gle.com, michael.a.bottini@...el.com,
        rafael@...nel.org, me@...ityamohan.in
Cc:     linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V10 0/4] Enable PCIe ASPM and LTR on select hardware



On 1/19/23 7:15 PM, 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.
> 
> 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
> 

Looks good to me.

Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>

> 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 | 97 ++++++++++++++++++++++++++----------
>  drivers/pci/pcie/aspm.c      | 54 ++++++++++++++++++++
>  include/linux/pci.h          |  7 +++
>  3 files changed, 132 insertions(+), 26 deletions(-)
> 
> 
> base-commit: 5dc4c995db9eb45f6373a956eb1f69460e69e6d4

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer