Re: [PATCH] PCI: Add missing link delays required by the PCIe spec
From: Rafael J. Wysocki
Date: Thu Aug 22 2019 - 18:23:50 EST
On Wednesday, August 21, 2019 2:45:19 PM CEST Mika Westerberg wrote:
> Currently Linux does not follow PCIe spec regarding the required delays
> after reset. A concrete example is a Thunderbolt add-in-card that
> consists of a PCIe switch and two PCIe endpoints:
>
> +-1b.0-[01-6b]----00.0-[02-6b]--+-00.0-[03]----00.0 TBT controller
> +-01.0-[04-36]-- DS hotplug port
> +-02.0-[37]----00.0 xHCI controller
> \-04.0-[38-6b]-- DS hotplug port
>
> The root port (1b.0) and the PCIe switch downstream ports are all PCIe
> gen3 so they support 8GT/s link speeds.
>
> We wait for the PCIe hierarchy to enter D3cold (runtime):
>
> pcieport 0000:00:1b.0: power state changed by ACPI to D3cold
>
> When it wakes up from D3cold, according to the PCIe 4.0 section 5.8 the
> PCIe switch is put to reset and its power is re-applied. This means that
> we must follow the rules in PCIe 4.0 section 6.6.1.
>
> For the PCIe gen3 ports we are dealing with here, the following applies:
>
> With a Downstream Port that supports Link speeds greater than 5.0
> GT/s, software must wait a minimum of 100 ms after Link training
> completes before sending a Configuration Request to the device
> immediately below that Port. Software can determine when Link training
> completes by polling the Data Link Layer Link Active bit or by setting
> up an associated interrupt (see Section 6.7.3.3).
>
> Translating this into the above topology we would need to do this (DLLLA
> stands for Data Link Layer Link Active):
>
> pcieport 0000:00:1b.0: wait for 100ms after DLLLA is set before access to 0000:01:00.0
> pcieport 0000:02:00.0: wait for 100ms after DLLLA is set before access to 0000:03:00.0
> pcieport 0000:02:02.0: wait for 100ms after DLLLA is set before access to 0000:37:00.0
>
> I've instrumented the kernel with additional logging so we can see the
> actual delays the kernel performs:
>
> pcieport 0000:00:1b.0: power state changed by ACPI to D0
> pcieport 0000:00:1b.0: waiting for D3cold delay of 100 ms
> pcieport 0000:00:1b.0: waking up bus
> pcieport 0000:00:1b.0: waiting for D3hot delay of 10 ms
> pcieport 0000:00:1b.0: restoring config space at offset 0x2c (was 0x60, writing 0x60)
> ...
> pcieport 0000:00:1b.0: PME# disabled
> pcieport 0000:01:00.0: restoring config space at offset 0x3c (was 0x1ff, writing 0x201ff)
> ...
> pcieport 0000:01:00.0: PME# disabled
> pcieport 0000:02:00.0: restoring config space at offset 0x3c (was 0x1ff, writing 0x201ff)
> ...
> pcieport 0000:02:00.0: PME# disabled
> pcieport 0000:02:01.0: restoring config space at offset 0x3c (was 0x1ff, writing 0x201ff)
> ...
> pcieport 0000:02:01.0: restoring config space at offset 0x4 (was 0x100000, writing 0x100407)
> pcieport 0000:02:01.0: PME# disabled
> pcieport 0000:02:02.0: restoring config space at offset 0x3c (was 0x1ff, writing 0x201ff)
> ...
> pcieport 0000:02:02.0: PME# disabled
> pcieport 0000:02:04.0: restoring config space at offset 0x3c (was 0x1ff, writing 0x201ff)
> ...
> pcieport 0000:02:04.0: PME# disabled
> pcieport 0000:02:01.0: PME# enabled
> pcieport 0000:02:01.0: waiting for D3hot delay of 10 ms
> pcieport 0000:02:04.0: PME# enabled
> pcieport 0000:02:04.0: waiting for D3hot delay of 10 ms
> thunderbolt 0000:03:00.0: restoring config space at offset 0x14 (was 0x0, writing 0x8a040000)
> ...
> thunderbolt 0000:03:00.0: PME# disabled
> xhci_hcd 0000:37:00.0: restoring config space at offset 0x10 (was 0x0, writing 0x73f00000)
> ...
> xhci_hcd 0000:37:00.0: PME# disabled
>
> For the switch upstream port (01:00.0) we wait for 100ms but not taking
> into account the DLLLA requirement. We then wait 10ms for D3hot -> D0
> transition of the root port and the two downstream hotplug ports. This
> means that we deviate from what the spec requires.
>
> Performing the same check for system sleep (s2idle) transitions we can
> see following when resuming from s2idle:
>
> pcieport 0000:00:1b.0: power state changed by ACPI to D0
> pcieport 0000:00:1b.0: restoring config space at offset 0x2c (was 0x60, writing 0x60)
> ...
> pcieport 0000:01:00.0: restoring config space at offset 0x3c (was 0x1ff, writing 0x201ff)
> ...
> pcieport 0000:02:02.0: restoring config space at offset 0x3c (was 0x1ff, writing 0x201ff)
> pcieport 0000:02:02.0: restoring config space at offset 0x2c (was 0x0, writing 0x0)
> pcieport 0000:02:01.0: restoring config space at offset 0x3c (was 0x1ff, writing 0x201ff)
> pcieport 0000:02:04.0: restoring config space at offset 0x3c (was 0x1ff, writing 0x201ff)
> pcieport 0000:02:02.0: restoring config space at offset 0x28 (was 0x0, writing 0x0)
> pcieport 0000:02:00.0: restoring config space at offset 0x3c (was 0x1ff, writing 0x201ff)
> pcieport 0000:02:02.0: restoring config space at offset 0x24 (was 0x10001, writing 0x1fff1)
> pcieport 0000:02:01.0: restoring config space at offset 0x2c (was 0x0, writing 0x60)
> pcieport 0000:02:02.0: restoring config space at offset 0x20 (was 0x0, writing 0x73f073f0)
> pcieport 0000:02:04.0: restoring config space at offset 0x2c (was 0x0, writing 0x60)
> pcieport 0000:02:01.0: restoring config space at offset 0x28 (was 0x0, writing 0x60)
> pcieport 0000:02:00.0: restoring config space at offset 0x2c (was 0x0, writing 0x0)
> pcieport 0000:02:02.0: restoring config space at offset 0x1c (was 0x101, writing 0x1f1)
> pcieport 0000:02:04.0: restoring config space at offset 0x28 (was 0x0, writing 0x60)
> pcieport 0000:02:01.0: restoring config space at offset 0x24 (was 0x10001, writing 0x1ff10001)
> pcieport 0000:02:00.0: restoring config space at offset 0x28 (was 0x0, writing 0x0)
> pcieport 0000:02:02.0: restoring config space at offset 0x18 (was 0x0, writing 0x373702)
> pcieport 0000:02:04.0: restoring config space at offset 0x24 (was 0x10001, writing 0x49f12001)
> pcieport 0000:02:01.0: restoring config space at offset 0x20 (was 0x0, writing 0x73e05c00)
> pcieport 0000:02:00.0: restoring config space at offset 0x24 (was 0x10001, writing 0x1fff1)
> pcieport 0000:02:04.0: restoring config space at offset 0x20 (was 0x0, writing 0x89f07400)
> pcieport 0000:02:01.0: restoring config space at offset 0x1c (was 0x101, writing 0x5151)
> pcieport 0000:02:00.0: restoring config space at offset 0x20 (was 0x0, writing 0x8a008a00)
> pcieport 0000:02:02.0: restoring config space at offset 0xc (was 0x10000, writing 0x10020)
> pcieport 0000:02:04.0: restoring config space at offset 0x1c (was 0x101, writing 0x6161)
> pcieport 0000:02:01.0: restoring config space at offset 0x18 (was 0x0, writing 0x360402)
> pcieport 0000:02:00.0: restoring config space at offset 0x1c (was 0x101, writing 0x1f1)
> pcieport 0000:02:04.0: restoring config space at offset 0x18 (was 0x0, writing 0x6b3802)
> pcieport 0000:02:02.0: restoring config space at offset 0x4 (was 0x100000, writing 0x100407)
> pcieport 0000:02:00.0: restoring config space at offset 0x18 (was 0x0, writing 0x30302)
> pcieport 0000:02:01.0: restoring config space at offset 0xc (was 0x10000, writing 0x10020)
> pcieport 0000:02:04.0: restoring config space at offset 0xc (was 0x10000, writing 0x10020)
> pcieport 0000:02:00.0: restoring config space at offset 0xc (was 0x10000, writing 0x10020)
> pcieport 0000:02:01.0: restoring config space at offset 0x4 (was 0x100000, writing 0x100407)
> pcieport 0000:02:04.0: restoring config space at offset 0x4 (was 0x100000, writing 0x100407)
> pcieport 0000:02:00.0: restoring config space at offset 0x4 (was 0x100000, writing 0x100407)
> xhci_hcd 0000:37:00.0: restoring config space at offset 0x10 (was 0x0, writing 0x73f00000)
> ...
> thunderbolt 0000:03:00.0: restoring config space at offset 0x14 (was 0x0, writing 0x8a040000)
>
> This is even worse. None of the mandatory delays are performed. If this
> would be S3 instead of s2idle then according to PCI FW spec 3.2 section
> 4.6.8. there is a specific _DSM that allows the OS to skip the delays
> but this platform does not provide the _DSM and does not go to S3 anyway
> so no firmware is involved that could already handle these delays.
>
> In this particular Intel Coffee Lake platform these delays are not
> actually needed because there is an additional delay as part of the ACPI
> power resource that is used to turn on power to the hierarchy but since
> that additional delay is not required by any of standards (PCIe, ACPI)
> it is not present in the Intel Ice Lake, for example where missing the
> mandatory delays causes pciehp to start tearing down the stack too early
> (links are not yet trained).
>
> There is also one reported case (see the bugzilla link below) where the
> missing delay causes xHCI on a Titan Ridge controller fail to runtime
> resume when USB-C dock is plugged.
>
> For this reason, introduce a new function pcie_wait_downstream_accessible()
> that is called on PCI core resume and runtime resume paths accordingly
> if downstream/root port with device below entered D3cold.
>
> This is second attempt to add the missing delays. The previous solution
> in commit c2bf1fc212f7 ("PCI: Add missing link delays required by the
> PCIe spec") was reverted because of two issues it caused:
>
> 1. One system become unresponsive after S3 resume due to PME service
> spinning in pcie_pme_work_fn(). The root port in question reports
> that the xHCI sent PME but the xHCI device itself does not have PME
> status set. The PME status bit is never cleared in the root port
> resulting the indefinite loop in pcie_pme_work_fn().
>
> 2. Slows down resume if the root/downstream port does not support
> Data Link Layer Active Reporting because pcie_wait_for_link_delay()
> waits 1100ms in that case.
>
> This version should avoid the above issues because we restrict the delay
> to happen only if the port went into D3cold (so it goes through reset)
> and only when there is no firmware involved on resume path (so the
> kernel is responsible for all the delays).
>
> Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=203885
> Reported-by: Kai-Heng Feng <kai.heng.feng@xxxxxxxxxxxxx>
> Tested-by: Kai-Heng Feng <kai.heng.feng@xxxxxxxxxxxxx>
> Signed-off-by: Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx>
Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> ---
> Hi all,
>
> As the changelog says this is reworked version that tries to avoid reported
> issues while at the same time fix the missing delays so we can get ICL
> systems and at least the one system with Titan Ridge controller working
> properly.
>
> @Matthias, @Paul and @Nicholas: it would be great if you could try the
> patch on top of v5.4-rc5+ and verify that it does not cause any issues on
> your systems.
>
> drivers/pci/pci-driver.c | 19 ++++++
> drivers/pci/pci.c | 127 ++++++++++++++++++++++++++++++++++++---
> drivers/pci/pci.h | 1 +
> 3 files changed, 137 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
> index a8124e47bf6e..9aec78ed8907 100644
> --- a/drivers/pci/pci-driver.c
> +++ b/drivers/pci/pci-driver.c
> @@ -918,6 +918,7 @@ static int pci_pm_resume_noirq(struct device *dev)
> {
> struct pci_dev *pci_dev = to_pci_dev(dev);
> struct device_driver *drv = dev->driver;
> + pci_power_t state = pci_dev->current_state;
> int error = 0;
>
> if (dev_pm_may_skip_resume(dev))
> @@ -947,6 +948,15 @@ static int pci_pm_resume_noirq(struct device *dev)
>
> pcie_pme_root_status_cleanup(pci_dev);
>
> + /*
> + * If resume involves firmware assume it takes care of any delays
> + * for now. For suspend-to-idle case we need to do that here before
> + * resuming PCIe port services to keep pciehp from tearing down the
> + * downstream devices too early.
> + */
> + if (state == PCI_D3cold && pm_suspend_no_platform())
> + pcie_wait_downstream_accessible(pci_dev);
> +
> if (drv && drv->pm && drv->pm->resume_noirq)
> error = drv->pm->resume_noirq(dev);
>
> @@ -1329,6 +1339,7 @@ static int pci_pm_runtime_resume(struct device *dev)
> int rc = 0;
> struct pci_dev *pci_dev = to_pci_dev(dev);
> const struct dev_pm_ops *pm = dev->driver ? dev->driver->pm : NULL;
> + pci_power_t state = pci_dev->current_state;
>
> /*
> * Restoring config space is necessary even if the device is not bound
> @@ -1344,6 +1355,14 @@ static int pci_pm_runtime_resume(struct device *dev)
> pci_enable_wake(pci_dev, PCI_D0, false);
> pci_fixup_device(pci_fixup_resume, pci_dev);
>
> + /*
> + * If the hierarcy went into D3cold wait for the link to be
> + * reactivated before resuming PCIe port services to keep pciehp
> + * from tearing down the downstream devices too early.
> + */
> + if (state == PCI_D3cold)
> + pcie_wait_downstream_accessible(pci_dev);
> +
> if (pm && pm->runtime_resume)
> rc = pm->runtime_resume(dev);
>
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 1b27b5af3d55..9ac50710f1d4 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -1025,15 +1025,11 @@ static void __pci_start_power_transition(struct pci_dev *dev, pci_power_t state)
> if (state == PCI_D0) {
> pci_platform_power_transition(dev, PCI_D0);
> /*
> - * Mandatory power management transition delays, see
> - * PCI Express Base Specification Revision 2.0 Section
> - * 6.6.1: Conventional Reset. Do not delay for
> - * devices powered on/off by corresponding bridge,
> - * because have already delayed for the bridge.
> + * Mandatory power management transition delays are handled
> + * in pci_pm_runtime_resume() of the corresponding
> + * downstream/root port.
> */
> if (dev->runtime_d3cold) {
> - if (dev->d3cold_delay && !dev->imm_ready)
> - msleep(dev->d3cold_delay);
> /*
> * When powering on a bridge from D3cold, the
> * whole hierarchy may be powered on into
> @@ -4607,14 +4603,17 @@ static int pci_pm_reset(struct pci_dev *dev, int probe)
>
> return pci_dev_wait(dev, "PM D3->D0", PCIE_RESET_READY_POLL_MS);
> }
> +
> /**
> - * pcie_wait_for_link - Wait until link is active or inactive
> + * pcie_wait_for_link_delay - Wait until link is active or inactive
> * @pdev: Bridge device
> * @active: waiting for active or inactive?
> + * @delay: Delay to wait after link has become active (in ms)
> *
> * Use this to wait till link becomes active or inactive.
> */
> -bool pcie_wait_for_link(struct pci_dev *pdev, bool active)
> +static bool pcie_wait_for_link_delay(struct pci_dev *pdev, bool active,
> + int delay)
> {
> int timeout = 1000;
> bool ret;
> @@ -4651,13 +4650,121 @@ bool pcie_wait_for_link(struct pci_dev *pdev, bool active)
> timeout -= 10;
> }
> if (active && ret)
> - msleep(100);
> + msleep(delay);
> else if (ret != active)
> pci_info(pdev, "Data Link Layer Link Active not %s in 1000 msec\n",
> active ? "set" : "cleared");
> return ret == active;
> }
>
> +/**
> + * pcie_wait_for_link - Wait until link is active or inactive
> + * @pdev: Bridge device
> + * @active: waiting for active or inactive?
> + *
> + * Use this to wait till link becomes active or inactive.
> + */
> +bool pcie_wait_for_link(struct pci_dev *pdev, bool active)
> +{
> + return pcie_wait_for_link_delay(pdev, active, 100);
> +}
> +
> +static int pcie_get_downstream_delay(struct pci_bus *bus)
> +{
> + struct pci_dev *pdev;
> + int min_delay = 100;
> + int max_delay = 0;
> +
> + list_for_each_entry(pdev, &bus->devices, bus_list) {
> + if (pdev->imm_ready)
> + min_delay = 0;
> + else if (pdev->d3cold_delay < min_delay)
> + min_delay = pdev->d3cold_delay;
> + if (pdev->d3cold_delay > max_delay)
> + max_delay = pdev->d3cold_delay;
> + }
> +
> + return max(min_delay, max_delay);
> +}
> +
> +/**
> + * pcie_wait_downstream_accessible - Wait downstream device to be accessible
> + * @pdev: PCIe port whose downstream device is waited
> + *
> + * Handle delays according to PCIe 4.0 section 6.6.1 before configuration
> + * access to the downstream device is permitted. If the port does not have
> + * any devices connected, does nothing.
> + *
> + * This is needed if the hierarchy below @pdev went through reset (after
> + * exit from D3cold back to D0uninitialized).
> + */
> +void pcie_wait_downstream_accessible(struct pci_dev *pdev)
> +{
> + struct pci_dev *child;
> + struct pci_bus *bus;
> + int delay;
> +
> + if (pci_pcie_type(pdev) != PCI_EXP_TYPE_ROOT_PORT &&
> + pci_pcie_type(pdev) != PCI_EXP_TYPE_DOWNSTREAM)
> + return;
> +
> + if (pci_dev_is_disconnected(pdev))
> + return;
> +
> + if (!pdev->bridge_d3)
> + return;
> +
> + bus = pdev->subordinate;
> + if (!bus)
> + return;
> +
> + child = list_first_entry_or_null(&bus->devices, struct pci_dev,
> + bus_list);
> + if (!child)
> + return;
> +
> + delay = pcie_get_downstream_delay(bus);
> + if (!delay)
> + return;
> +
> + /*
> + * If downstream port does not support speeds greater than 5 GT/s
> + * need to wait minimum 100ms. For higher speeds (gen3) we need to
> + * wait first for the data link layer to become active.
> + *
> + * However, 100ms is the minimum and the spec says that the
> + * software must allow at least 1s before it can determine that the
> + * device that did not respond is a broken device. Also there is
> + * evidence that the 100ms is not always enough so what we do here
> + * is that we wait for the minimum 100ms (possibly after link
> + * training completes) and then probe for the device presence once.
> + * If we still don't get response we wait for another 100ms just to
> + * give it some additional time to complete its initialization.
> + */
> + if (pcie_get_speed_cap(pdev) <= PCIE_SPEED_5_0GT) {
> + dev_dbg(&pdev->dev, "waiting downstream link for %d ms\n",
> + delay);
> + msleep(delay);
> + } else {
> + dev_dbg(&pdev->dev,
> + "waiting downstream link for %d ms after activation\n",
> + delay);
> + if (!pcie_wait_for_link_delay(pdev, true, delay)) {
> + /*
> + * If the link did not train, no need to wait
> + * further the device is probably gone.
> + */
> + return;
> + }
> + }
> +
> + if (!pci_device_is_present(child)) {
> + dev_dbg(&child->dev,
> + "waiting for additional 100 ms for the device to become accessible\n");
> + msleep(100);
> + }
> +}
> +
> void pci_reset_secondary_bus(struct pci_dev *dev)
> {
> u16 ctrl;
> diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
> index d22d1b807701..9a83fcf612ca 100644
> --- a/drivers/pci/pci.h
> +++ b/drivers/pci/pci.h
> @@ -498,6 +498,7 @@ void pcie_do_recovery(struct pci_dev *dev, enum pci_channel_state state,
> u32 service);
>
> bool pcie_wait_for_link(struct pci_dev *pdev, bool active);
> +void pcie_wait_downstream_accessible(struct pci_dev *pdev);
> #ifdef CONFIG_PCIEASPM
> void pcie_aspm_init_link_state(struct pci_dev *pdev);
> void pcie_aspm_exit_link_state(struct pci_dev *pdev);
>