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Message-ID: <20241213182845.GA3423569@bhelgaas>
Date: Fri, 13 Dec 2024 12:28:45 -0600
From: Bjorn Helgaas <helgaas@...nel.org>
To: Jian-Hong Pan <jhp@...lessos.org>
Cc: Krzysztof Wilczyński <kw@...ux.com>,
Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>,
Nirmal Patel <nirmal.patel@...ux.intel.com>,
linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
linux@...lessos.org,
Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
"David E. Box" <david.e.box@...ux.intel.com>
Subject: Re: [PATCH v13] PCI/ASPM: Make pci_save_aspm_l1ss_state save both
child and parent's L1SS configuration
On Fri, Dec 13, 2024 at 12:37:24PM +0800, Jian-Hong Pan wrote:
> Bjorn Helgaas <helgaas@...nel.org> 於 2024年12月13日 週五 上午7:03寫道：
> > On Fri, Nov 15, 2024 at 03:22:02PM +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.
> ...
> > I think the important thing here is that currently
> > pci_save_aspm_l1ss_state() saves only the child L1SS state, but
> > pci_restore_aspm_l1ss_state() restores both parent and child, and the
> > parent state is garbage.
> >
> > Obviously nothing specific to VMD or NVMe or SATA.
> >
> > > To avoid pci_restore_aspm_l1ss_state() restore wrong value to the parent's
> > > L1SS config like this example, make pci_save_aspm_l1ss_state() save the
> > > parent's L1SS config, if the PCI device has a parent.
> >
> > I tried to simplify the commit log and the patch so it's a little more
> > parallel with pci_restore_aspm_l1ss_state(). Please comment and test.
> >
> > Bjorn
> >
> > commit c93935e3ac92 ("PCI/ASPM: Save parent L1SS config in pci_save_aspm_l1ss_state()")
> > Author: Jian-Hong Pan <jhp@...lessos.org>
> > Date: Fri Nov 15 15:22:02 2024 +0800
> >
> > PCI/ASPM: Save parent L1SS config in pci_save_aspm_l1ss_state()
> >
> > After 17423360a27a ("PCI/ASPM: Save L1 PM Substates Capability for
> > suspend/resume"), pci_save_aspm_l1ss_state(dev) saves the L1SS state for
> > "dev", and pci_restore_aspm_l1ss_state(dev) restores the state for both
> > "dev" and its parent.
> >
> > The problem is that unless pci_save_state() has been used in some other
> > path and has already saved the parent L1SS state, we will restore junk to
> > the parent, which means the L1 Substates likely won't work correctly.
> >
> > Save the L1SS config for both the device and its parent in
> > pci_save_aspm_l1ss_state(). When restoring, we need both because L1SS must
> > be enabled at the parent (the Downstream Port) before being enabled at the
> > child (the Upstream Port).
> >
> > Link: https://lore.kernel.org/r/20241115072200.37509-3-jhp@endlessos.org
> > Fixes: 17423360a27a ("PCI/ASPM: Save L1 PM Substates Capability for suspend/resume")
> > Closes: https://bugzilla.kernel.org/show_bug.cgi?id=218394
> > Suggested-by: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
> > Signed-off-by: Jian-Hong Pan <jhp@...lessos.org>
> > [bhelgaas: parallel save/restore structure, simplify commit log]
>
> Thanks for the simplification!
> Tested on my Asus B1400CEAE. Both the "dev" (NVMe) and the parent (PCI
> bridge) keep the correct L1SS config.
>
> Tested-by: Jian-Hong Pan <jhp@...lessos.org>
Thanks, I applied this on pci/aspm for v6.14 since this is a pretty
old problem, and AFAICT it's a power consumption issue, not something
that is functionally broken. We might be able to make a case for
v6.13 if my understanding is incorrect.
Ilpo, David, I dropped your reviewed-by since I changed the patch
significantly; let me know if you see any issue or if you want to add
your reviewed-by.
> > diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
> > index 28567d457613..e0bc90597dca 100644
> > --- a/drivers/pci/pcie/aspm.c
> > +++ b/drivers/pci/pcie/aspm.c
> > @@ -81,24 +81,47 @@ void pci_configure_aspm_l1ss(struct pci_dev *pdev)
> >
> > void pci_save_aspm_l1ss_state(struct pci_dev *pdev)
> > {
> > + struct pci_dev *parent = pdev->bus->self;
> > struct pci_cap_saved_state *save_state;
> > - u16 l1ss = pdev->l1ss;
> > u32 *cap;
> >
> > + /*
> > + * If this is a Downstream Port, we never restore the L1SS state
> > + * directly; we only restore it when we restore the state of the
> > + * Upstream Port below it.
> > + */
> > + if (pcie_downstream_port(pdev) || !parent)
> > + return;
> > +
> > + if (!pdev->l1ss || !parent->l1ss)
> > + return;
> > +
> > /*
> > * Save L1 substate configuration. The ASPM L0s/L1 configuration
> > * in PCI_EXP_LNKCTL_ASPMC is saved by pci_save_pcie_state().
> > */
> > - if (!l1ss)
> > - return;
> > -
> > save_state = pci_find_saved_ext_cap(pdev, PCI_EXT_CAP_ID_L1SS);
> > if (!save_state)
> > return;
> >
> > cap = &save_state->cap.data[0];
> > - pci_read_config_dword(pdev, l1ss + PCI_L1SS_CTL2, cap++);
> > - pci_read_config_dword(pdev, l1ss + PCI_L1SS_CTL1, cap++);
> > + pci_read_config_dword(pdev, pdev->l1ss + PCI_L1SS_CTL2, cap++);
> > + pci_read_config_dword(pdev, pdev->l1ss + PCI_L1SS_CTL1, cap++);
> > +
> > + if (parent->state_saved)
> > + return;
> > +
> > + /*
> > + * Save parent's L1 substate configuration so we have it for
> > + * pci_restore_aspm_l1ss_state(pdev) to restore.
> > + */
> > + save_state = pci_find_saved_ext_cap(parent, PCI_EXT_CAP_ID_L1SS);
> > + if (!save_state)
> > + return;
> > +
> > + cap = &save_state->cap.data[0];
> > + pci_read_config_dword(parent, parent->l1ss + PCI_L1SS_CTL2, cap++);
> > + pci_read_config_dword(parent, parent->l1ss + PCI_L1SS_CTL1, cap++);
> > }
> >
> > void pci_restore_aspm_l1ss_state(struct pci_dev *pdev)
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