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

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Message-ID: <20240624082144.10265-2-jhp@endlessos.org>
Date: Mon, 24 Jun 2024 16:21:45 +0800
From: Jian-Hong Pan <jhp@...lessos.org>
To: Bjorn Helgaas <helgaas@...nel.org>
Cc: Francisco Munoz <francisco.munoz.ruiz@...ux.intel.com>,
	Johan Hovold <johan@...nel.org>,
	David Box <david.e.box@...ux.intel.com>,
	Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
	Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>,
	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	Damien Le Moal <dlemoal@...nel.org>,
	Nirmal Patel <nirmal.patel@...ux.intel.com>,
	Jonathan Derrick <jonathan.derrick@...ux.dev>,
	linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux@...lessos.org,
	Jian-Hong Pan <jhp@...lessos.org>
Subject: [PATCH v6 3/3] PCI: vmd: Drop resetting PCI bus action after scan mapped PCI child bus

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@...lessos.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);
-- 
2.45.2