Re: [PATCH v12 3/3] PCI/ASPM: Make pci_save_aspm_l1ss_state save both child and parent's L1SS configuration

[David E. Box]

Hi Jian-Hong,

On Tue, 2024-10-01 at 16:34 +0800, Jian-Hong Pan wrote:
> PCI devices' parameters on the VMD bus have been programmed properly
> originally. But, cleared after pci_reset_bus() and have not been restored
> correctly. This leads the link's L1.2 between PCIe Root Port and child
> device gets wrong configs.
> 
> Here is a failed example on ASUS B1400CEAE with enabled VMD. Both PCIe
> bridge and NVMe device should have the same LTR1.2_Threshold value.
> However, they are configured as different values in this case:
> 
> 10000:e0:06.0 PCI bridge [0604]: Intel Corporation 11th Gen Core Processor
> PCIe Controller [8086:9a09] (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=0us LTR1.2_Threshold=0ns
>     L1SubCtl2: T_PwrOn=0us
> 
> 10000:e1:00.0 Non-Volatile memory controller [0108]: Sandisk Corp WD Blue
> SN550 NVMe SSD [15b7:5009] (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=101376ns
>     L1SubCtl2: T_PwrOn=50us
> 
> Here is VMD mapped PCI device tree:
> 
> -+-[0000:00]-+-00.0  Intel Corporation Device 9a04
>  | ...
>  \-[10000:e0]-+-06.0-[e1]----00.0  Sandisk Corp WD Blue SN550 NVMe SSD
>               \-17.0  Intel Corporation Tiger Lake-LP SATA Controller
> 
> When pci_reset_bus() resets the bus [e1] of the NVMe, it only saves and
> restores NVMe's state before and after reset. Then, when it restores the
> NVMe's state, ASPM code restores L1SS for both the parent bridge and the
> NVMe in pci_restore_aspm_l1ss_state(). The NVMe's L1SS is restored
> correctly. But, the parent bridge's L1SS is restored with a wrong value 0x0
> because the parent bridge's L1SS wasn't saved by pci_save_aspm_l1ss_state()
> before reset.
> 
> So, if the PCI device has a parent, make pci_save_aspm_l1ss_state() save
> the parent's L1SS configuration, too. This is symmetric on
> pci_restore_aspm_l1ss_state().
> 
> Link:
> https://lore.kernel.org/linux-pci/CAPpJ_eexU0gCHMbXw_z924WxXw0+B6SdS4eG9oGpEX1wmnMLkQ@xxxxxxxxxxxxxx/
> Closes: https://bugzilla.kernel.org/show_bug.cgi?id=218394
> Fixes: 17423360a27a ("PCI/ASPM: Save L1 PM Substates Capability for
> suspend/resume")
> Suggested-by: Ilpo Järvinen <ilpo.jarvinen@xxxxxxxxxxxxxxx>
> Signed-off-by: Jian-Hong Pan <jhp@xxxxxxxxxxxxx>
> ---
> v9:
> - Drop the v8 fix about drivers/pci/pcie/aspm.c. Use this in VMD instead.
> 
> v10:
> - Drop the v9 fix about drivers/pci/controller/vmd.c
> - Fix in PCIe ASPM to make it symmetric between pci_save_aspm_l1ss_state()
>   and pci_restore_aspm_l1ss_state()
> 
> v11:
> - Introduce __pci_save_aspm_l1ss_state as a resusable helper function
>   which is same as the original pci_configure_aspm_l1ss
> - Make pci_save_aspm_l1ss_state invoke __pci_save_aspm_l1ss_state for
>   both child and parent devices
> - Smooth the commit message
> 
> v12:
> - Update the commit message
> 
>  drivers/pci/pcie/aspm.c | 20 +++++++++++++++++++-
>  1 file changed, 19 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
> index bd0a8a05647e..17cdf372f7e0 100644
> --- a/drivers/pci/pcie/aspm.c
> +++ b/drivers/pci/pcie/aspm.c
> @@ -79,7 +79,7 @@ void pci_configure_aspm_l1ss(struct pci_dev *pdev)
>  			ERR_PTR(rc));
>  }
>  
> -void pci_save_aspm_l1ss_state(struct pci_dev *pdev)
> +static void __pci_save_aspm_l1ss_state(struct pci_dev *pdev)
>  {
>  	struct pci_cap_saved_state *save_state;
>  	u16 l1ss = pdev->l1ss;
> @@ -101,6 +101,24 @@ void pci_save_aspm_l1ss_state(struct pci_dev *pdev)
>  	pci_read_config_dword(pdev, l1ss + PCI_L1SS_CTL1, cap++);
>  }
>  
> +void pci_save_aspm_l1ss_state(struct pci_dev *pdev)
> +{
> +	struct pci_dev *parent;
> +
> +	__pci_save_aspm_l1ss_state(pdev);
> +
> +	/*
> +	 * To be symmetric on pci_restore_aspm_l1ss_state(), save parent's L1
> +	 * substate configuration, if the parent has not saved state.
> +	 */
> +	if (!pdev->bus || !pdev->bus->self)
> +		return;
> +
> +	parent = pdev->bus->self;
> +	if (!parent->state_saved)
> +		__pci_save_aspm_l1ss_state(parent);
> +}
> +
>  void pci_restore_aspm_l1ss_state(struct pci_dev *pdev)
>  {
>  	struct pci_cap_saved_state *pl_save_state, *cl_save_state;

This took a while to debug and find a solution. Thanks for continuing to work on
this.

Reviewed-by: David E. Box <david.e.box@xxxxxxxxxxxxxxx