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Message-ID: <CAPpJ_eeO9j38VGaukrw79dqQAZ7Z8+QMOvTbymyV9=fbQBqFzw@mail.gmail.com>
Date: Mon, 12 Aug 2024 16:18:22 +0800
From: Jian-Hong Pan <jhp@...lessos.org>
To: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
Cc: "David E. Box" <david.e.box@...ux.intel.com>, Bjorn Helgaas <helgaas@...nel.org>,
Johan Hovold <johan@...nel.org>,
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>,
Paul M Stillwell Jr <paul.m.stillwell.jr@...el.com>, linux-pci@...r.kernel.org,
LKML <linux-kernel@...r.kernel.org>, linux@...lessos.org
Subject: Re: [PATCH v8 4/4] PCI/ASPM: Fix L1.2 parameters when enable link state
Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com> 於 2024年8月8日 週四 下午5:49寫道：
>
> On Wed, 7 Aug 2024, David E. Box wrote:
>
> > On Wed, 2024-08-07 at 14:18 +0300, Ilpo Järvinen wrote:
> > > On Wed, 7 Aug 2024, Jian-Hong Pan wrote:
> > >
> > > > David E. Box <david.e.box@...ux.intel.com> 於 2024年8月6日 週二 上午4:26寫道：
> > > > >
> > > > > Hi Jian-Hong,
> > > > >
> > > > > On Fri, 2024-08-02 at 16:24 +0800, Jian-Hong Pan wrote:
> > > > > > Jian-Hong Pan <jhp@...lessos.org> 於 2024年7月19日 週五 下午4:04寫道：
> > > > > > >
> > > > > > > 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@...lessos.org>
> > > > > > > ---
> > > > > > > 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()"
> > > > > > >
> > > > > > > v6:
> > > > > > > - Skipped
> > > > > > >
> > > > > > > v7:
> > > > > > > - Pick back and rebase on the new version kernel
> > > > > > > - Drop the link state flag check. And, always config link state's
> > > > > > > timing
> > > > > > > parameters
> > > > > > >
> > > > > > > v8:
> > > > > > > - Because pcie_aspm_get_link() might return the link as NULL, move
> > > > > > > getting the link's parent and child devices after check the link is
> > > > > > > not NULL. This avoids NULL memory access.
> > > > > > >
> > > > > > > drivers/pci/pcie/aspm.c | 15 +++++++++++++++
> > > > > > > 1 file changed, 15 insertions(+)
> > > > > > >
> > > > > > > diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
> > > > > > > index 5db1044c9895..55ff1d26fcea 100644
> > > > > > > --- a/drivers/pci/pcie/aspm.c
> > > > > > > +++ b/drivers/pci/pcie/aspm.c
> > > > > > > @@ -1411,9 +1411,15 @@ 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);
> > > > > > > + u32 parent_l1ss_cap, child_l1ss_cap;
> > > > > > > + struct pci_dev *parent, *child;
> > > > > > >
> > > > > > > if (!link)
> > > > > > > return -EINVAL;
> > > > > > > +
> > > > > > > + parent = link->pdev;
> > > > > > > + child = link->downstream;
> > > > > > > +
> > > > > > > /*
> > > > > > > * A driver requested that ASPM be enabled on this device, but
> > > > > > > * if we don't have permission to manage ASPM (e.g., on ACPI
> > > > > > > @@ -1428,6 +1434,15 @@ static int __pci_enable_link_state(struct
> > > > > > > pci_dev
> > > > > > > *pdev, int state, bool locked)
> > > > > > > if (!locked)
> > > > > > > down_read(&pci_bus_sem);
> > > > > > > mutex_lock(&aspm_lock);
> > > > > > > + /*
> > > > > > > + * 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.
> > > > > > > + */
> > > > > > > + 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);
> > > > >
> > > > > I still don't think this is the place to recalculate the L1.2 parameters
> > > > > especially when know the calculation was done but was cleared by
> > > > > pci_bus_reset(). Can't we just do a pci_save/restore_state() before/after
> > > > > pci_bus_reset() in vmd.c?
> > > >
> > > > I have not thought pci_save/restore_state() around pci_bus_reset()
> > > > before. It is an interesting direction.
> > > >
> > > > So, I prepare modification below for test. Include "[PATCH v8 1/4]
> > > > PCI: vmd: Set PCI devices to D0 before enable PCI PM's L1 substates",
> > > > too. Then, both the PCIe bridge and the PCIe device have the same
> > > > LTR_L1.2_THRESHOLD 101376ns as expected.
> > > >
> > > > diff --git a/drivers/pci/controller/vmd.c b/drivers/pci/controller/vmd.c
> > > > index bbf4a47e7b31..6b8dd4f30127 100644
> > > > --- a/drivers/pci/controller/vmd.c
> > > > +++ b/drivers/pci/controller/vmd.c
> > > > @@ -727,6 +727,18 @@ static void vmd_copy_host_bridge_flags(struct
> > > > pci_host_bridge *root_bridge,
> > > > vmd_bridge->native_dpc = root_bridge->native_dpc;
> > > > }
> > > >
> > > > +static int vmd_pci_save_state(struct pci_dev *pdev, void *userdata)
> > > > +{
> > > > + pci_save_state(pdev);
> > > > + return 0;
> > > > +}
> > > > +
> > > > +static int vmd_pci_restore_state(struct pci_dev *pdev, void *userdata)
> > > > +{
> > > > + pci_restore_state(pdev);
> > > > + return 0;
> > > > +}
> > > > +
> > > > /*
> > > > * Enable ASPM and LTR settings on devices that aren't configured by BIOS.
> > > > */
> > > > @@ -927,6 +939,7 @@ static int vmd_enable_domain(struct vmd_dev *vmd,
> > > > unsigned long features)
> > > > pci_scan_child_bus(vmd->bus);
> > > > vmd_domain_reset(vmd);
> > > >
> > > > + pci_walk_bus(vmd->bus, vmd_pci_save_state, NULL);
> > > > /* 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
> > > > @@ -945,6 +958,7 @@ static int vmd_enable_domain(struct vmd_dev *vmd,
> > > > unsigned long features)
> > > > break;
> > > > }
> > > > }
> > > > + pci_walk_bus(vmd->bus, vmd_pci_restore_state, NULL);
> > >
> > > Why not call pci_reset_bus() (or __pci_reset_bus()) then in
> > > vmd_enable_domain() which preserves state unlike pci_reset_bus()?
> > >
> > > (Don't tell me naming of these functions is a horrible mess. :-/)
> >
> > Hmm. So this *is* calling pci_reset_bus().
>
> Yeah, I managed to get confused by the names myself, I somehow
> ended up thinking it calls pci_bus_reset() which is not correct...
>
> > L1.2 configuration has specific
> > ordering requirements for changes to parent & child devices. Could be why it's
> > not getting restored properly.
>
> Indeed, it has to be something else since the patch above doesn't even
> restore anything because dev->state_saved should get set to false by the
> first pci_restore_state() called from
> __pci_reset_bus() -> pci_bus_restore_locked() -> pci_dev_restore(), I
> think!?
Inspired by Ilpo's comment. I add some debug messages based on
linux-next's tag 'next-20240809' to understand the code path of
pci_reset_bus():
diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index ffaaca0978cb..3ee71374f1de 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -5133,8 +5133,10 @@ static void pci_dev_save_and_disable(struct pci_dev *dev)
* races with ->remove() by the device lock, which must be held by
* the caller.
*/
- if (err_handler && err_handler->reset_prepare)
+ if (err_handler && err_handler->reset_prepare) {
+ pci_info(dev, "%s: %pF\n", __func__,
err_handler->reset_prepare);
err_handler->reset_prepare(dev);
+ }
/*
* Wake-up device prior to save. PM registers default to D0 after
@@ -5144,6 +5146,7 @@ static void pci_dev_save_and_disable(struct pci_dev *dev)
pci_set_power_state(dev, PCI_D0);
pci_save_state(dev);
+ pci_info(dev, "%s: PCI state_saved is %s\n", __func__,
dev->state_saved ? "true" : "false");
/*
* Disable the device by clearing the Command register, except for
* INTx-disable which is set. This not only disables MMIO and I/O port
@@ -5655,6 +5658,10 @@ static void
pci_bus_save_and_disable_locked(struct pci_bus *bus)
struct pci_dev *dev;
list_for_each_entry(dev, &bus->devices, bus_list) {
+ pci_info(dev, "%s: PCI state_saved is %s, and %s subordinate\n",
+ __func__,
+ dev->state_saved ? "true" : "false",
+ dev->subordinate ? "has" : "does not have");
pci_dev_save_and_disable(dev);
if (dev->subordinate)
pci_bus_save_and_disable_locked(dev->subordinate);
@@ -5671,6 +5678,10 @@ static void pci_bus_restore_locked(struct pci_bus *bus)
struct pci_dev *dev;
list_for_each_entry(dev, &bus->devices, bus_list) {
+ pci_info(dev, "%s: PCI state_saved is %s, and %s subordinate\n",
+ __func__,
+ dev->state_saved ? "true" : "false",
+ dev->subordinate ? "has" : "does not have");
pci_dev_restore(dev);
if (dev->subordinate)
pci_bus_restore_locked(dev->subordinate);
@@ -5786,8 +5797,10 @@ static int pci_bus_reset(struct pci_bus *bus, bool probe)
if (!bus->self || !pci_bus_resettable(bus))
return -ENOTTY;
- if (probe)
+ if (probe) {
+ pci_info(bus->self, "%s: probe is true. So return 0
directly", __func__);
return 0;
+ }
pci_bus_lock(bus);
@@ -5858,10 +5871,12 @@ static int __pci_reset_bus(struct pci_bus *bus)
int rc;
rc = pci_bus_reset(bus, PCI_RESET_PROBE);
+ pci_info(bus->self, "%s: pci_bus_reset() returns %d\n", __func__, rc);
if (rc)
return rc;
if (pci_bus_trylock(bus)) {
+ pci_info(bus->self, "%s: pci_bus_trylock() returns
true\n", __func__);
pci_bus_save_and_disable_locked(bus);
might_sleep();
rc = pci_bridge_secondary_bus_reset(bus->self);
@@ -5881,6 +5896,7 @@ static int __pci_reset_bus(struct pci_bus *bus)
*/
int pci_reset_bus(struct pci_dev *pdev)
{
+ pci_info(pdev, "%s: %s", __func__,
!pci_probe_reset_slot(pdev->slot) ? "true" : "false");
return (!pci_probe_reset_slot(pdev->slot)) ?
__pci_reset_slot(pdev->slot) : __pci_reset_bus(pdev->bus);
}
And, have the information of VMD PCIe devices with the built kernel:
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=0us LTR1.2_Threshold=0ns
L1SubCtl2: T_PwrOn=0us
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
We can see the NVMe has expected LTR1.2_Threshold=101376ns, but the
PCIe bridge has LTR1.2_Threshold=0ns.
Then, check the dmesg. I notice the debug messages:
pci 10000:e0:06.0: PCI bridge to [bus e1]
pci 10000:e0:06.0: Primary bus is hard wired to 0
pci 10000:e1:00.0: pci_reset_bus: false
pci 10000:e0:06.0: pci_bus_reset: probe is true. So return 0 directly
pci 10000:e0:06.0: __pci_reset_bus: pci_bus_reset() returns 0
pci 10000:e0:06.0: __pci_reset_bus: pci_bus_trylock() returns true
pci 10000:e1:00.0: pci_bus_save_and_disable_locked: PCI state_saved is
false, and does not have subordinate
pci 10000:e1:00.0: pci_dev_save_and_disable: PCI state_saved is true
Freeing initrd memory: 75236K
pci 10000:e1:00.0: pci_bus_restore_locked: PCI state_saved is true,
and does not have subordinate
So, the code path is:
vmd_enable_domain()
pci_reset_bus()
__pci_reset_bus()
pci_bus_reset()
pci_bus_save_and_disable_locked()
pci_dev_save_and_disable()
pci_bus_restore_locked()
pci_dev_restore()
And, from the debug messages, I learned only NVMe 10000:e1:00.0 does
pci_save/restore_state. But, the PCIe bridge 10000:e0:06.0 does not.
So, PCIe bridge 10000:e0:06.0 does not restore state correctly.
Besides, it is NVMe 10000:e1:00.0's bus [e1] been reset, not the VMD's
bus in vmd_enable_domain().
* Bus "e1" has only NVMe 10000:e1:00.0
* VMD's bus in vmd_enable_domain() has PCIe bridge 10000:e0:06.0, NVMe
10000:e1:00.0 and SATA Controller 10000:e0:17.0.
Here is the PCI tree:
-+-[0000:00]-+-00.0 Intel Corporation Device 9a04
| +-02.0 Intel Corporation Tiger Lake-LP GT2 [UHD Graphics G4]
| +-04.0 Intel Corporation TigerLake-LP Dynamic Tuning
Processor Participant
| +-06.0 Intel Corporation RST VMD Managed Controller
| +-07.0-[01-2b]--
| +-08.0 Intel Corporation GNA Scoring Accelerator module
| +-0a.0 Intel Corporation Tigerlake Telemetry Aggregator Driver
| +-0d.0 Intel Corporation Tiger Lake-LP Thunderbolt 4 USB
Controller
| +-0d.2 Intel Corporation Tiger Lake-LP Thunderbolt 4 NHI #0
| +-0e.0 Intel Corporation Volume Management Device NVMe
RAID Controller
| +-14.0 Intel Corporation Tiger Lake-LP USB 3.2 Gen 2x1
xHCI Host Controller
| +-14.2 Intel Corporation Tiger Lake-LP Shared SRAM
| +-14.3 Intel Corporation Wi-Fi 6 AX201
| +-15.0 Intel Corporation Tiger Lake-LP Serial IO I2C Controller #0
| +-15.1 Intel Corporation Tiger Lake-LP Serial IO I2C Controller #1
| +-16.0 Intel Corporation Tiger Lake-LP Management Engine Interface
| +-17.0 Intel Corporation RST VMD Managed Controller
| +-1f.0 Intel Corporation Tiger Lake-LP LPC Controller
| +-1f.3 Intel Corporation Tiger Lake-LP Smart Sound
Technology Audio Controller
| +-1f.4 Intel Corporation Tiger Lake-LP SMBus Controller
| +-1f.5 Intel Corporation Tiger Lake-LP SPI Controller
| \-1f.6 Intel Corporation Ethernet Connection (13) I219-V
\-[10000:e0]-+-06.0-[e1]----00.0 Sandisk Corp WD Blue SN550 NVMe SSD
\-17.0 Intel Corporation Tiger Lake-LP SATA Controller
According the findings above, to ensure the devices on the VMD bus
have correctly states, seems pci_save_state() all the devices before
pci_reset_bus(), and pci_restore_state() all the devices after
pci_reset_bus() is the correct answer.
Jian-Hong Pan
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