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Message-ID: <20241105225949.GA1493775@bhelgaas>
Date: Tue, 5 Nov 2024 16:59:49 -0600
From: Bjorn Helgaas <helgaas@...nel.org>
To: Jian-Hong Pan <jhp@...lessos.org>
Cc: Johan Hovold <johan@...nel.org>,
David Box <david.e.box@...ux.intel.com>,
Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...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 v12 3/3] PCI/ASPM: Make pci_save_aspm_l1ss_state save
both child and parent's L1SS configuration
On Tue, Oct 01, 2024 at 04:34:42PM +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.
There's nothing specific to VMD here, is there? This whole log looks
like it should be made generic. The VMD *example* is OK, but the
justification should not be VMD-specific. This last paragraph seems
to be the kernel of the whole thing, and I don't think it's specific
to either VMD or NVMe.
> 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@mail.gmail.com/
> 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@...ux.intel.com>
> Signed-off-by: Jian-Hong Pan <jhp@...lessos.org>
> ---
> 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);
Is there any point in saving the "pdev" state if there's no parent?
> + /*
> + * 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;
Is "pdev->bus == NULL" possible here even though it doesn't seem
possible in pci_restore_aspm_l1ss_state()?
> + parent = pdev->bus->self;
> + if (!parent->state_saved)
> + __pci_save_aspm_l1ss_state(parent);
> +}
I see the suggestion for a helper here, but I'm not convinced.
pci_save_aspm_l1ss_state() and pci_restore_aspm_l1ss_state() should
*look* similar, and a helper makes them less similar.
I think you should go to some effort to follow the
pci_restore_aspm_l1ss_state() structure, as much as possible doing the
same declarations, checks, and lookups in the same order, e.g.:
struct pci_cap_saved_state *pl_save_state, *cl_save_state;
struct pci_dev *parent = pdev->bus->self;
if (pcie_downstream_port(pdev) || !parent)
return;
if (!pdev->l1ss || !parent->l1ss)
return;
cl_save_state = pci_find_saved_ext_cap(pdev, PCI_EXT_CAP_ID_L1SS);
pl_save_state = pci_find_saved_ext_cap(parent, PCI_EXT_CAP_ID_L1SS);
if (!cl_save_state || !pl_save_state)
return;
Bjorn
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