Re: [PATCH v6 3/3] PCI: vmd: Drop resetting PCI bus action after scan mapped PCI child bus

Jian-Hong Pan
2024-06-25T10:32:31Z

Paul M Stillwell Jr <paul.m.stillwell.jr@intel.com> 於 2024年6月24日 週一 下午11:39寫道：
>
> On 6/24/2024 8:24 AM, Nirmal Patel wrote:
> > On Mon, 24 Jun 2024 16:21:45 +0800
> > Jian-Hong Pan <jhp@endlessos.org> wrote:
> >
> >> According to "PCIe r6.0, sec 5.5.4", before enabling ASPM L1.2 on the
> >> PCIe Root Port and the child device, they should be programmed with
> >> the same LTR1.2_Threshold value. However, they have different values
> >> on VMD mapped PCI child bus. For example, Asus B1400CEAE's VMD mapped
> >> PCI bridge and NVMe SSD controller have different LTR1.2_Threshold
> >> values:
> >>
> >> 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
> >>
> >> After debug in detail, both of the VMD mapped PCI bridge and the NVMe
> >> SSD controller have been configured properly with the same
> >> LTR1.2_Threshold value. But, become misconfigured after reset the VMD
> >> mapped PCI bus which is introduced from commit 0a584655ef89 ("PCI:
> >> vmd: Fix secondary bus reset for Intel bridges") and commit
> >> 6aab5622296b ("PCI: vmd: Clean up domain before enumeration"). So,
> >> drop the resetting PCI bus action after scan VMD mapped PCI child bus.
> >>
> >> Signed-off-by: Jian-Hong Pan <jhp@endlessos.org>
> >> ---
> >> v6:
> >> - Introduced based on the discussion
> >> https://lore.kernel.org/linux-pci/CAPpJ_efYWWxGBopbSQHB=Y2+1RrXFR2XWeqEhGTgdiw3XX0Jmw@mail.gmail.com/
> >>
> >> drivers/pci/controller/vmd.c | 20 --------------------
> >> 1 file changed, 20 deletions(-)
> >>
> >> diff --git a/drivers/pci/controller/vmd.c
> >> b/drivers/pci/controller/vmd.c index 5309afbe31f9..af413cdb4f4e 100644
> >> --- a/drivers/pci/controller/vmd.c
> >> +++ b/drivers/pci/controller/vmd.c
> >> @@ -793,7 +793,6 @@ static int vmd_enable_domain(struct vmd_dev *vmd,
> >> unsigned long features) resource_size_t offset[2] = {0};
> >> resource_size_t membar2_offset = 0x2000;
> >> struct pci_bus *child;
> >> - struct pci_dev *dev;
> >> int ret;
> >>
> >> /*
> >> @@ -935,25 +934,6 @@ 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);
> >> - 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);
> >
> > Thanks for the patch.
> >
> > pci_reset_bus is required to avoid failure in vmd domain creation
> > during multiple soft reboots test. So I believe we can't just remove
> > it without proper testing. vmd_pm_enable_quirk happens after
> > pci_reset_bus, then how is it resetting LTR1.2_Threshold value?
> >
> > Thanks
> > -nirmal
>
> To follow up on what Nirmal said: why can't you set the threshold value
> in vmd_pm_enable_quirk() since we look at LTR there?

Looks like setting the threshold value again in vmd_pm_enable_quirk()
is the preferred direction?
If so, I can prepare for that in the next version patch.

Jian-Hong Pan