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

[Paul M Stillwell Jr <paul.m.stillwell.jr@intel.com>]

On 6/25/2024 3:31 AM, Jian-Hong Pan wrote:
> 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
> 

Yes, I think keeping all the LTR code together is the best thing.

Paul