linux-kernel - Re: [PATCH v4 1/3] PCI: vmd: Enable PCI PM's L1 substates of remapped PCIe Root Port and NVMe

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Message-ID: <5b5daf03-55ab-45a6-99aa-390a4f4163d4@linux.intel.com>
Date: Fri, 1 Mar 2024 22:32:07 -0800
From: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
To: Jian-Hong Pan <jhp@...lessos.org>, Bjorn Helgaas <helgaas@...nel.org>,
 Johan Hovold <johan@...nel.org>, David Box <david.e.box@...ux.intel.com>,
 Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
Cc: 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, linux@...lessos.org
Subject: Re: [PATCH v4 1/3] PCI: vmd: Enable PCI PM's L1 substates of remapped
 PCIe Root Port and NVMe


On 2/15/24 10:24 PM, Jian-Hong Pan wrote:
> The remapped PCIe Root Port and NVMe have PCI PM L1 substates capability,
> but they are disabled originally.
>
> Here is a failed example on ASUS B1400CEAE:
>
> 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
>
> Power on all of the VMD remapped PCI devices before enable PCI-PM L1 PM
> Substates by following PCI Express Base Specification Revision 6.0, section
> 5.5.4.
>
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=218394
> Signed-off-by: Jian-Hong Pan <jhp@...lessos.org>
> ---
Code wise it looks fine to me.

Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
> v2:
> - Power on the VMD remapped devices with pci_set_power_state_locked()
> - Prepare the PCIe LTR parameters before enable L1 Substates
> - Add note into the comments of both pci_enable_link_state() and
>   pci_enable_link_state_locked() for kernel-doc.
> - The original patch set can be split as individual patches.
>
> v3:
> - Re-send for the missed version information.
> - Split drivers/pci/pcie/aspm.c modification into following patches.
> - Fix the comment for enasuring the PCI devices in D0.
>
> v4:
> - The same
>
>  drivers/pci/controller/vmd.c | 13 +++++++++----
>  1 file changed, 9 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/pci/controller/vmd.c b/drivers/pci/controller/vmd.c
> index 87b7856f375a..6aca3f77724c 100644
> --- a/drivers/pci/controller/vmd.c
> +++ b/drivers/pci/controller/vmd.c
> @@ -751,11 +751,9 @@ static int vmd_pm_enable_quirk(struct pci_dev *pdev, void *userdata)
>  	if (!(features & VMD_FEAT_BIOS_PM_QUIRK))
>  		return 0;
>  
> -	pci_enable_link_state_locked(pdev, PCIE_LINK_STATE_ALL);
> -
>  	pos = pci_find_ext_capability(pdev, PCI_EXT_CAP_ID_LTR);
>  	if (!pos)
> -		return 0;
> +		goto out_enable_link_state;
>  
>  	/*
>  	 * Skip if the max snoop LTR is non-zero, indicating BIOS has set it
> @@ -763,7 +761,7 @@ static int vmd_pm_enable_quirk(struct pci_dev *pdev, void *userdata)
>  	 */
>  	pci_read_config_dword(pdev, pos + PCI_LTR_MAX_SNOOP_LAT, &ltr_reg);
>  	if (!!(ltr_reg & (PCI_LTR_VALUE_MASK | PCI_LTR_SCALE_MASK)))
> -		return 0;
> +		goto out_enable_link_state;
>  
>  	/*
>  	 * Set the default values to the maximum required by the platform to
> @@ -775,6 +773,13 @@ static int vmd_pm_enable_quirk(struct pci_dev *pdev, void *userdata)
>  	pci_write_config_dword(pdev, pos + PCI_LTR_MAX_SNOOP_LAT, ltr_reg);
>  	pci_info(pdev, "VMD: Default LTR value set by driver\n");
>  
> +out_enable_link_state:
Nit: Since you are also power on device, may be a generic name is better? Like
out_state_change or update_device_state? But it is upto you.
> +	/*
> +	 * Ensure devices are in D0 before enabling PCI-PM L1 PM Substates, per
> +	 * PCIe r6.0, sec 5.5.4.
> +	 */
> +	pci_set_power_state_locked(pdev, PCI_D0);
> +	pci_enable_link_state_locked(pdev, PCIE_LINK_STATE_ALL);
>  	return 0;
>  }
>  

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer