linux-kernel - Re: [PATCH v3 3/3] PCI/ASPM: Fix L1SS parameters & only enable supported features when enable link state

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Message-ID: <0e7944d410664153b506ea584d92cd6bb0a93f6a.camel@linux.intel.com>
Date: Wed, 07 Feb 2024 08:02:48 -0800
From: "David E. Box" <david.e.box@...ux.intel.com>
To: Jian-Hong Pan <jhp@...lessos.org>, Bjorn Helgaas <helgaas@...nel.org>, 
 Johan Hovold <johan@...nel.org>, Ilpo Järvinen
 <ilpo.jarvinen@...ux.intel.com>
Cc: Mika Westerberg <mika.westerberg@...ux.intel.com>, Nirmal Patel
 <nirmal.patel@...ux.intel.com>, Jonathan Derrick
 <jonathan.derrick@...ux.dev>,  linux-pci@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux@...lessos.org
Subject: Re: [PATCH v3 3/3] PCI/ASPM: Fix L1SS parameters & only enable
 supported features when enable link state

On Wed, 2024-02-07 at 19:18 +0800, Jian-Hong Pan wrote:
> The original __pci_enable_link_state() configs the links directly without:
> * Check the L1 substates features which are supported, or not
> * Calculate & program related parameters for L1.2, such as T_POWER_ON,
>   Common_Mode_Restore_Time, and LTR_L1.2_THRESHOLD
> 
> This leads some supported L1 PM substates of the link between VMD remapped
> PCIe Root Port and NVMe get wrong configs when a caller tries to enabled
> them.
> 
> Here is a failed example on ASUS B1400CEAE with enabled VMD:
> 
> 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
> 
> This patch initializes the link's L1 PM substates to get the supported
> features and programs relating paramters, if some of them are going to be
> enabled in __pci_enable_link_state(). Then, enables the L1 PM substates if
> the caller intends to enable them and they are supported.
> 
> 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
> 
>  drivers/pci/pcie/aspm.c | 12 +++++++-----
>  1 file changed, 7 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
> index a39d2ee744cb..c866971cae70 100644
> --- a/drivers/pci/pcie/aspm.c
> +++ b/drivers/pci/pcie/aspm.c
> @@ -1389,14 +1389,16 @@ static int __pci_enable_link_state(struct pci_dev
> *pdev, int state, bool locked)
>                 link->aspm_default |= ASPM_STATE_L0S;
>         if (state & PCIE_LINK_STATE_L1)
>                 link->aspm_default |= ASPM_STATE_L1;
> -       /* L1 PM substates require L1 */
> -       if (state & PCIE_LINK_STATE_L1_1)
> +       if (state & ASPM_STATE_L1_2_MASK)
> +               aspm_l1ss_init(link);

This mixes ASPM_STATE flags with PCIE_LINK_STATE register mapping. This may work
but I don't know if it's intended to. Rather do,

    if (link->default & ASPM_STATE_L1_2_MASK)

after collecting all of the states to be enabled.

I understand that you are calling aspm_l1ss_init() to do the L1.2 calculations
but it does more than this that you don't need. Maybe it would be more
appropriate to call aspm_calc_l12_info() directly through an additional function
that finds the parent and determines both ends of the link support L1SS.

> +       /* L1 PM substates require L1 and should be in supported list */
> +       if (state & link->aspm_support & PCIE_LINK_STATE_L1_1)
>                 link->aspm_default |= ASPM_STATE_L1_1 | ASPM_STATE_L1;
> -       if (state & PCIE_LINK_STATE_L1_2)
> +       if (state & link->aspm_support & PCIE_LINK_STATE_L1_2)
>                 link->aspm_default |= ASPM_STATE_L1_2 | ASPM_STATE_L1;
> -       if (state & PCIE_LINK_STATE_L1_1_PCIPM)
> +       if (state & link->aspm_support & PCIE_LINK_STATE_L1_1_PCIPM)
>                 link->aspm_default |= ASPM_STATE_L1_1_PCIPM | ASPM_STATE_L1;
> -       if (state & PCIE_LINK_STATE_L1_2_PCIPM)
> +       if (state & link->aspm_support & PCIE_LINK_STATE_L1_2_PCIPM)
>                 link->aspm_default |= ASPM_STATE_L1_2_PCIPM | ASPM_STATE_L1;
>         pcie_config_aspm_link(link, policy_to_aspm_state(link));
>  

I don't think these changes are necessary. pcie_config_aspm_link() already
checks link->aspm_capable which was initialized from link->aspm_support.

David