Re: [PATCH v5 4/4] PCI/ASPM: Fix L1.2 parameters when enable link state

From: Jian-Hong Pan
Date: Mon Jun 03 2024 - 03:30:03 EST

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Bjorn Helgaas <helgaas@xxxxxxxxxx> 於 2024年5月4日週六上午6:28寫道：
>
> [+cc Francisco]
>
> On Fri, May 03, 2024 at 12:15:49PM -0700, David E. Box wrote:
> > On Fri, 2024-05-03 at 17:45 +0800, Jian-Hong Pan wrote:
> > > David E. Box <david.e.box@xxxxxxxxxxxxxxx> 於 2024年5月1日週三上午2:26寫道：
> > > > On Tue, 2024-04-30 at 15:46 +0800, Jian-Hong Pan wrote:
> > > > > David E. Box <david.e.box@xxxxxxxxxxxxxxx> 於 2024年4月27日週六上午8:03寫道：
> > > > > > On Wed, 2024-04-24 at 19:02 +0800, Jian-Hong Pan wrote:
> > > > > > > Currently, when enable link's L1.2 features with
> > > > > > > __pci_enable_link_state(),
> > > > > > > it configs the link directly without ensuring related L1.2 parameters,
> > > > > > > such
> > > > > > > as T_POWER_ON, Common_Mode_Restore_Time, and LTR_L1.2_THRESHOLD have
> > > > > > > been
> > > > > > > programmed.
> > > > > > >
> > > > > > > This leads the link's L1.2 between PCIe Root Port and child device
> > > > > > > gets
> > > > > > > wrong configs when a caller tries to enabled it.
> > > > > > >
> > > > > > > Here is a failed example on ASUS B1400CEAE with enabled VMD:
> > > > > > >
> > > > > > > 10000:e0:06.0 PCI bridge: Intel Corporation 11th Gen Core Processor
> > > > > > > PCIe
> > > > > > > Controller (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=45us LTR1.2_Threshold=101376ns
> > > > > > > L1SubCtl2: T_PwrOn=50us
> > > > > > >
> > > > > > > 10000:e1:00.0 Non-Volatile memory controller: Sandisk Corp WD Blue
> > > > > > > SN550
> > > > > > > NVMe
> > > > > > > SSD (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=0ns
> > > > > > > L1SubCtl2: T_PwrOn=10us
> > > > > > >
> > > > > > > According to "PCIe r6.0, sec 5.5.4", before enabling ASPM L1.2 on the
> > > > > > > PCIe
> > > > > > > Root Port and the child NVMe, they should be programmed with the same
> > > > > > > LTR1.2_Threshold value. However, they have different values in this
> > > > > > > case.
> > > > > > >
> > > > > > > Invoke aspm_calc_l12_info() to program the L1.2 parameters properly
> > > > > > > before
> > > > > > > enable L1.2 bits of L1 PM Substates Control Register in
> > > > > > > __pci_enable_link_state().
> > > > > > >
> > > > > > > Link: https://bugzilla.kernel.org/show_bug.cgi?id=218394
> > > > > > > Signed-off-by: Jian-Hong Pan <jhp@xxxxxxxxxxxxx>
> > > > > > > ---
> > > > > > > v2:
> > > > > > > - Prepare the PCIe LTR parameters before enable L1 Substates
> > > > > > >
> > > > > > > v3:
> > > > > > > - Only enable supported features for the L1 Substates part
> > > > > > >
> > > > > > > v4:
> > > > > > > - Focus on fixing L1.2 parameters, instead of re-initializing whole
> > > > > > > L1SS
> > > > > > >
> > > > > > > v5:
> > > > > > > - Fix typo and commit message
> > > > > > > - Split introducing aspm_get_l1ss_cap() to "PCI/ASPM: Introduce
> > > > > > > aspm_get_l1ss_cap()"
> > > > > > >
> > > > > > > drivers/pci/pcie/aspm.c | 12 ++++++++++++
> > > > > > > 1 file changed, 12 insertions(+)
> > > > > > >
> > > > > > > diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
> > > > > > > index c55ac11faa73..553327dee991 100644
> > > > > > > --- a/drivers/pci/pcie/aspm.c
> > > > > > > +++ b/drivers/pci/pcie/aspm.c
> > > > > > > @@ -1402,6 +1402,8 @@ EXPORT_SYMBOL(pci_disable_link_state);
> > > > > > > static int __pci_enable_link_state(struct pci_dev *pdev, int state,
> > > > > > > bool
> > > > > > > locked)
> > > > > > > {
> > > > > > > struct pcie_link_state *link = pcie_aspm_get_link(pdev);
> > > > > > > + struct pci_dev *child = link->downstream, *parent = link-
> > > > > > > >pdev;
> > > > > > > + u32 parent_l1ss_cap, child_l1ss_cap;
> > > > > > >
> > > > > > > if (!link)
> > > > > > > return -EINVAL;
> > > > > > > @@ -1433,6 +1435,16 @@ static int __pci_enable_link_state(struct
> > > > > > > pci_dev
> > > > > > > *pdev, int state, bool locked)
> > > > > > > link->aspm_default |= ASPM_STATE_L1_1_PCIPM |
> > > > > > > ASPM_STATE_L1;
> > > > > > > if (state & PCIE_LINK_STATE_L1_2_PCIPM)
> > > > > > > link->aspm_default |= ASPM_STATE_L1_2_PCIPM |
> > > > > > > ASPM_STATE_L1;
> > > > > > > + /*
> > > > > > > + * Ensure L1.2 parameters: Common_Mode_Restore_Times,
> > > > > > > T_POWER_ON
> > > > > > > and
> > > > > > > + * LTR_L1.2_THRESHOLD are programmed properly before enable
> > > > > > > bits
> > > > > > > for
> > > > > > > + * L1.2, per PCIe r6.0, sec 5.5.4.
> > > > > > > + */
> > > > > > > + if (state & link->aspm_capable & ASPM_STATE_L1_2_MASK) {
> > > > > >
> > > > > > This is still mixing PCIE_LINK_STATE flags with ASPM_STATE flags.
>
> FWIW, Ilpo has removed the ASPM_STATE flags, so eventually this would
> have to be updated to apply on the current pci/aspm branch. We're at
> rc6 already, so likely this will end up being v6.11 material so you'll
> be able to rebase on v6.10-rc1 when it comes out.
>
> > > > > Thanks for your review, but I notice some description in PCIe spec,
> > > > > 5.5.4 L1 PM Substates Configuration:
> > > > > "Prior to setting either or both of the enable bits for L1.2, the
> > > > > values for TPOWER_ON, Common_Mode_Restore_Time, and, if the ASPM L1.2
> > > > > Enable bit is to be Set, the LTR_L1.2_THRESHOLD (both Value and Scale
> > > > > fields) must be programmed." => I think this includes both "ASPM L1.2
> > > > > Enable" and "PCI-PM L1.2 Enable" bits.
> > > >
> > > > That's fine. While the spec clearly calls out the ASPM L1.2 Enable bit here,
> > > > I
> > > > see no harm in including PCI-PM L1.2 in that check. This is what the code
> > > > already does in aspm_l1ss_init().
> > > >
> > > > The issue is the mixed used of two different types of flags that don't have
> > > > the
> > > > same meaning. 'state' contains PCIE_LINK_STATE flags which are part of the
> > > > caller API to the pci_<enabled/disable>_link_state() functions. The
> > > > ASPM_STATE
> > > > flags are used internally to aspm.c to track all states and their meaningful
> > > > combinations such as ASPM_STATE_L1_2_MASK which includes ASPM L1.2 and PCI-
> > > > PM
> > > > L1.2. You should not do bit operations between them.
> > > >
> > > > Also, you should not require that the timings be calculated only if L1_2 is
> > > > enabled. You should calculate the timings as long as it's capable. This is
> > > > also
> > > > what aspm_l1ss_init() does.
> > > >
> > > > The confusion might be over the fact that you are having
> > > > __pci_enable_link_state() call aspm_calc_l12_info(). This should have been
> > > > handled during initialization of the link in aspm_l1ss_init() and I'm not
> > > > sure
> > > > why it didn't. Maybe it's because, for VMD, ASPM default state would have
> > > > started out all disabled and this somehow led to aspm_l1ss_init() not
> > > > getting
> > > > called. But looking through the code I don't see it. It would be great if
> > > > you
> > > > can confirm why they weren't calculated before.
> > >
> > > I debug it again. If I delete the pci_reset_bus() in vmd controller like:
> > >
> > > diff --git a/drivers/pci/controller/vmd.c b/drivers/pci/controller/vmd.c
> > > index 87b7856f375a..39bfda4350bf 100644
> > > --- a/drivers/pci/controller/vmd.c
> > > +++ b/drivers/pci/controller/vmd.c
> > > @@ -930,25 +930,6 @@ static int vmd_enable_domain(struct vmd_dev *vmd,
> > > unsigned long features)
> > > pci_scan_child_bus(vmd->bus);
> > > vmd_domain_reset(vmd);
> > >
> > > - /* When Intel VMD is enabled, the OS does not discover the Root Ports
> > > - * owned by Intel VMD within the MMCFG space. pci_reset_bus() applies
> > > - * a reset to the parent of the PCI device supplied as argument. This
> > > - * is why we pass a child device, so the reset can be triggered at
> > > - * the Intel bridge level and propagated to all the children in the
> > > - * hierarchy.
> > > - */
> > > - list_for_each_entry(child, &vmd->bus->children, node) {
> > > - if (!list_empty(&child->devices)) {
> > > - dev = list_first_entry(&child->devices,
> > > - struct pci_dev, bus_list);
> > > - ret = pci_reset_bus(dev);
> >
> > Hi Nirmal. It's not clear to me from the comment why there's a need to do a bus
> > reset. It looks like it is causing misconfiguration of the ASPM L1.2 timings
> > which would have been done above in pci_scan_child_bus(). Jian-Hong discovered
> > that without the above reset code, the timings are correct.
>
> I don't understand that comment either. If we don't enumerate the
> Root Ports below VMD, it sounds like something is wrong, and reset
> doesn't seem like the right fix.
>
> The reset was added by 0a584655ef89 ("PCI: vmd: Fix secondary bus
> reset for Intel bridges") for guest reboots. Maybe Francisco can shed
> more light on it.

Hi Francisco,

We found: the VMD remapped PCI devices' (PCIe bridge and NVMe SSD)
PCIe LTR1.2_Threshold is correct originally, but becomes misconfigured
after "pci_reset_bus()" in "vmd_enable_domain()".

Here is an example that the PCI bridge and its child NVMe SSD have
different LTR1.2_Threshold:

10000:e0:06.0 PCI bridge: Intel Corporation 11th Gen Core Processor
PCIe Controller (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=45us LTR1.2_Threshold=101376ns
L1SubCtl2: T_PwrOn=50us

10000:e1:00.0 Non-Volatile memory controller: Sandisk Corp WD Blue
SN550 NVMe SSD (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=0ns
L1SubCtl2: T_PwrOn=10us

It will be great to have your knowledge: Is resetting a PCI device at
bridge level still needed here?

Thanks,
Jian-Hong Pan

> > This patch recalculates the timings during the call to pci_enable_link_state()
> > which is called during pci_bus_walk() below. Originally I thought the
> > recalculation might have been needed by all callers to pci_enabled_link_state()
> > since it changes the default BIOS configuration. But it looks like the reset is
> > the cause and only the VMD driver would need the recalculation as a result. I
> > don't see qcom doing a reset.
> >
> > Jian-Hong, given this (and assuming the reset is needed) I would not call
> > aspm_calc_l12_info() from pci_enable_link_state() but instead try redoing the
> > whole ASPM initialization right after the resets are done, maybe by calling
> > pci_scan_child_bus() again. What do you think Bjorn?
>
> I would expect pci_reset_bus() to save and restore config space, but
> if we don't enumerate all the devices correctly, I suppose we wouldn't
> do that for devices we don't know about.
>
> > > - if (ret)
> > > - pci_warn(dev, "can't reset device: %d\n",
> > > ret);
> > > -
> > > - break;
> > > - }
> > > - }
> > > -
> > > pci_assign_unassigned_bus_resources(vmd->bus);
> > >
> > > pci_walk_bus(vmd->bus, vmd_pm_enable_quirk, &features);
> > >
> > > Although PCI-PM_L1.2 is disabled, both PCI bridge and the NVMe's
> > > LTR1.2_Threshold are configured as 101376ns:
> > >
> > > 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=45us LTR1.2_Threshold=101376ns
> > > L1SubCtl2: T_PwrOn=50us
> > >
> > > 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
> > >
> > > Then, I apply the patch "PCI: vmd: Set PCI devices to D0 before enable
> > > PCI PM's L1 substates". Both PCI bridge and the NVMe's PCI-PM_L1.2 is
> > > enabled and LTR1.2_Threshold is configured as 101376ns.
> > >
> > > 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=45us LTR1.2_Threshold=101376ns
> > > L1SubCtl2: T_PwrOn=50us
> > >
> > > 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
> > >
> > > I do not know VMD very much. However, from the test result, it looks
> > > like LTR1.2_Threshold has been configured properly originally. But,
> > > LTR1.2_Threshold is misconfigured by 'pci_reset_bus()'.
> > > ...
> > > > > > 'state' should not even matter.
> > > > > > The timings should always be calculated and programmed as long
> > > > > > as L1_2 is capable. That way the timings are ready even if L1_2 isn't
> > > > > > being
> > > > > > enabled now (in case the user enables it later).
> > > > > >
> > > > > > > + parent_l1ss_cap = aspm_get_l1ss_cap(parent);
> > > > > > > + child_l1ss_cap = aspm_get_l1ss_cap(child);
> > > > > > > + aspm_calc_l12_info(link, parent_l1ss_cap,
> > > > > > > child_l1ss_cap);
> > > > > > > + }
> > > > > > > pcie_config_aspm_link(link, policy_to_aspm_state(link));
> > > > > > >
> > > > > > > link->clkpm_default = (state & PCIE_LINK_STATE_CLKPM) ? 1 : 0;
> > > > > >
> > > >
> >

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