linux-kernel - Re: [PATCH v5 4/4] PCI/ASPM: Fix L1.2 parameters when enable link state

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Message-ID: <f111371300624b6f94f0746dbae66bd49f405eea.camel@linux.intel.com>
Date: Fri, 26 Apr 2024 17:03:03 -0700
From: "David E. Box" <david.e.box@...ux.intel.com>
To: Jian-Hong Pan <jhp@...lessos.org>, Bjorn Helgaas <helgaas@...nel.org>
Cc: Johan Hovold <johan@...nel.org>, Ilpo Järvinen
 <ilpo.jarvinen@...ux.intel.com>, Kuppuswamy Sathyanarayanan
 <sathyanarayanan.kuppuswamy@...ux.intel.com>, Mika Westerberg
 <mika.westerberg@...ux.intel.com>, Damien Le Moal <dlemoal@...nel.org>, 
 Nirmal Patel <nirmal.patel@...ux.intel.com>, Jonathan Derrick
 <jonathan.derrick@...ux.dev>,  linux-pci@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 4/4] PCI/ASPM: Fix L1.2 parameters when enable link
 state

Hi Jian-Hong,

On Wed, 2024-04-24 at 19:02 +0800, Jian-Hong Pan wrote:
> Currently, when enable link's L1.2 features with __pci_enable_link_state(),
> it configs the link directly without ensuring related L1.2 parameters, such
> as T_POWER_ON, Common_Mode_Restore_Time, and LTR_L1.2_THRESHOLD have been
> programmed.
> 
> This leads the link's L1.2 between PCIe Root Port and child device gets
> wrong configs when a caller tries to enabled it.
> 
> Here is a failed example on ASUS B1400CEAE with enabled VMD:
> 
> 10000:e0:06.0 PCI bridge: Intel Corporation 11th Gen Core Processor PCIe
> Controller (rev 01) (prog-if 00 [Normal decode])
>     ...
>     Capabilities: [200 v1] L1 PM Substates
>         L1SubCap: PCI-PM_L1.2+ PCI-PM_L1.1+ ASPM_L1.2+ ASPM_L1.1+
> L1_PM_Substates+
>                   PortCommonModeRestoreTime=45us PortTPowerOnTime=50us
>         L1SubCtl1: PCI-PM_L1.2- PCI-PM_L1.1- ASPM_L1.2+ ASPM_L1.1-
>                    T_CommonMode=45us LTR1.2_Threshold=101376ns
>         L1SubCtl2: T_PwrOn=50us
> 
> 10000:e1:00.0 Non-Volatile memory controller: Sandisk Corp WD Blue SN550 NVMe
> SSD (rev 01) (prog-if 02 [NVM Express])
>     ...
>     Capabilities: [900 v1] L1 PM Substates
>         L1SubCap: PCI-PM_L1.2+ PCI-PM_L1.1- ASPM_L1.2+ ASPM_L1.1-
> L1_PM_Substates+
>                   PortCommonModeRestoreTime=32us PortTPowerOnTime=10us
>         L1SubCtl1: PCI-PM_L1.2- PCI-PM_L1.1- ASPM_L1.2+ ASPM_L1.1-
>                    T_CommonMode=0us LTR1.2_Threshold=0ns
>         L1SubCtl2: T_PwrOn=10us
> 
> According to "PCIe r6.0, sec 5.5.4", before enabling ASPM L1.2 on the PCIe
> Root Port and the child NVMe, they should be programmed with the same
> LTR1.2_Threshold value. However, they have different values in this case.
> 
> Invoke aspm_calc_l12_info() to program the L1.2 parameters properly before
> enable L1.2 bits of L1 PM Substates Control Register in
> __pci_enable_link_state().
> 
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=218394
> Signed-off-by: Jian-Hong Pan <jhp@...lessos.org>
> ---
> v2:
> - Prepare the PCIe LTR parameters before enable L1 Substates
> 
> v3:
> - Only enable supported features for the L1 Substates part
> 
> v4:
> - Focus on fixing L1.2 parameters, instead of re-initializing whole L1SS
> 
> v5:
> - Fix typo and commit message
> - Split introducing aspm_get_l1ss_cap() to "PCI/ASPM: Introduce
>   aspm_get_l1ss_cap()"
> 
>  drivers/pci/pcie/aspm.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
> index c55ac11faa73..553327dee991 100644
> --- a/drivers/pci/pcie/aspm.c
> +++ b/drivers/pci/pcie/aspm.c
> @@ -1402,6 +1402,8 @@ EXPORT_SYMBOL(pci_disable_link_state);
>  static int __pci_enable_link_state(struct pci_dev *pdev, int state, bool
> locked)
>  {
>         struct pcie_link_state *link = pcie_aspm_get_link(pdev);
> +       struct pci_dev *child = link->downstream, *parent = link->pdev;
> +       u32 parent_l1ss_cap, child_l1ss_cap;
>  
>         if (!link)
>                 return -EINVAL;
> @@ -1433,6 +1435,16 @@ static int __pci_enable_link_state(struct pci_dev
> *pdev, int state, bool locked)
>                 link->aspm_default |= ASPM_STATE_L1_1_PCIPM | ASPM_STATE_L1;
>         if (state & PCIE_LINK_STATE_L1_2_PCIPM)
>                 link->aspm_default |= ASPM_STATE_L1_2_PCIPM | ASPM_STATE_L1;
> +       /*
> +        * Ensure L1.2 parameters: Common_Mode_Restore_Times, T_POWER_ON and
> +        * LTR_L1.2_THRESHOLD are programmed properly before enable bits for
> +        * L1.2, per PCIe r6.0, sec 5.5.4.
> +        */
> +       if (state & link->aspm_capable & ASPM_STATE_L1_2_MASK) {

This is still mixing PCIE_LINK_STATE flags with ASPM_STATE flags. 'state' should
not even matter. The timings should always be calculated and programmed as long
as L1_2 is capable. That way the timings are ready even if L1_2 isn't being
enabled now (in case the user enables it later).

David

> +               parent_l1ss_cap = aspm_get_l1ss_cap(parent);
> +               child_l1ss_cap = aspm_get_l1ss_cap(child);
> +               aspm_calc_l12_info(link, parent_l1ss_cap, child_l1ss_cap);
> +       }
>         pcie_config_aspm_link(link, policy_to_aspm_state(link));
>  
>         link->clkpm_default = (state & PCIE_LINK_STATE_CLKPM) ? 1 : 0;