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 6/24/2024 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?

Paul