Re: [PATCH v9 00/14] pci: Work around ASMedia ASM2824 PCIe link training failures

Bjorn Helgaas
2023-06-14T23:20:50Z

On Sun, Jun 11, 2023 at 06:19:08PM +0100, Maciej W. Rozycki wrote:
> Hi,
>
> This is v9 of the change to work around a PCIe link training phenomenon
> where a pair of devices both capable of operating at a link speed above
> 2.5GT/s seems unable to negotiate the link speed and continues training
> indefinitely with the Link Training bit switching on and off repeatedly
> and the data link layer never reaching the active state.
>
> With several requests addressed and a few extra issues spotted this
> version has now grown to 14 patches. It has been verified for device
> enumeration with and without PCI_QUIRKS enabled, using the same piece of
> RISC-V hardware as previously. Hot plug or reset events have not been
> verified, as this is difficult if at all feasible with hardware in
> question.
>
> Last iteration:
> <https://lore.kernel.org/r/alpine.DEB.2.21.2304060100160.13659@angie.orcam.me.uk/>,
> and my input to it:
> <https://lore.kernel.org/r/alpine.DEB.2.21.2306080224280.36323@angie.orcam.me.uk/>.

Thanks, I applied these to pci/enumeration for v6.5.

I tweaked a few things, so double-check to be sure I didn't break
something:

- Moved dev->link_active_reporting init to set_pcie_port_type()
because it does other PCIe-related stuff.

- Reordered to keep all the link_active_reporting things together.

- Reordered to clean up & factor pcie_retrain_link() before exposing
it to the rest of the PCI core.

- Moved pcie_retrain_link() a little earlier to keep it next to
pcie_wait_for_link_status().

- Squashed the stubs into the actual quirk so we don't have the
intermediate state where we call the stubs but they never do
anything (let me know if there's a reason we need your order).

- Inline pcie_parent_link_retrain(), which seemed like it didn't add
enough to be worthwhile.

Interdiff below:

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 80694e2574b8..f11268924c8f 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -1153,27 +1153,16 @@ void pci_resume_bus(struct pci_bus *bus)
pci_walk_bus(bus, pci_resume_one, NULL);
}

-/**
- * pcie_parent_link_retrain - Check and retrain link we are downstream from
- * @dev: PCI device to handle.
- *
- * Return TRUE if the link was retrained, FALSE otherwise.
- */
-static bool pcie_parent_link_retrain(struct pci_dev *dev)
-{
- struct pci_dev *bridge;
-
- bridge = pci_upstream_bridge(dev);
- if (bridge)
- return pcie_failed_link_retrain(bridge);
- else
- return false;
-}
-
static int pci_dev_wait(struct pci_dev *dev, char *reset_type, int timeout)
{
- bool retrain = true;
int delay = 1;
+ bool retrain = false;
+ struct pci_dev *bridge;
+
+ if (pci_is_pcie(dev)) {
+ retrain = true;
+ bridge = pci_upstream_bridge(dev);
+ }

/*
* After reset, the device should not silently discard config
@@ -1201,9 +1190,9 @@ static int pci_dev_wait(struct pci_dev *dev, char *reset_type, int timeout)
}

if (delay > PCI_RESET_WAIT) {
- if (retrain) {
+ if (retrain && bridge) {
retrain = false;
- if (pcie_parent_link_retrain(dev)) {
+ if (pcie_failed_link_retrain(bridge)) {
delay = 1;
continue;
}
@@ -4914,6 +4903,38 @@ static bool pcie_wait_for_link_status(struct pci_dev *pdev,
return (lnksta & lnksta_mask) == lnksta_match;
}

+/**
+ * pcie_retrain_link - Request a link retrain and wait for it to complete
+ * @pdev: Device whose link to retrain.
+ * @use_lt: Use the LT bit if TRUE, or the DLLLA bit if FALSE, for status.
+ *
+ * Retrain completion status is retrieved from the Link Status Register
+ * according to @use_lt. It is not verified whether the use of the DLLLA
+ * bit is valid.
+ *
+ * Return TRUE if successful, or FALSE if training has not completed
+ * within PCIE_LINK_RETRAIN_TIMEOUT_MS milliseconds.
+ */
+bool pcie_retrain_link(struct pci_dev *pdev, bool use_lt)
+{
+ u16 lnkctl;
+
+ pcie_capability_read_word(pdev, PCI_EXP_LNKCTL, &lnkctl);
+ lnkctl |= PCI_EXP_LNKCTL_RL;
+ pcie_capability_write_word(pdev, PCI_EXP_LNKCTL, lnkctl);
+ if (pdev->clear_retrain_link) {
+ /*
+ * Due to an erratum in some devices the Retrain Link bit
+ * needs to be cleared again manually to allow the link
+ * training to succeed.
+ */
+ lnkctl &= ~PCI_EXP_LNKCTL_RL;
+ pcie_capability_write_word(pdev, PCI_EXP_LNKCTL, lnkctl);
+ }
+
+ return pcie_wait_for_link_status(pdev, use_lt, !use_lt);
+}
+
/**
* pcie_wait_for_link_delay - Wait until link is active or inactive
* @pdev: Bridge device
@@ -4968,37 +4989,6 @@ bool pcie_wait_for_link(struct pci_dev *pdev, bool active)
return pcie_wait_for_link_delay(pdev, active, 100);
}

-/**
- * pcie_retrain_link - Request a link retrain and wait for it to complete
- * @pdev: Device whose link to retrain.
- * @use_lt: Use the LT bit if TRUE, or the DLLLA bit if FALSE, for status.
- *
- * Retrain completion status is retrieved from the Link Status Register
- * according to @use_lt. It is not verified whether the use of the DLLLA
- * bit is valid.
- *
- * Return TRUE if successful, or FALSE if training has not completed.
- */
-bool pcie_retrain_link(struct pci_dev *pdev, bool use_lt)
-{
- u16 lnkctl;
-
- pcie_capability_read_word(pdev, PCI_EXP_LNKCTL, &lnkctl);
- lnkctl |= PCI_EXP_LNKCTL_RL;
- pcie_capability_write_word(pdev, PCI_EXP_LNKCTL, lnkctl);
- if (pdev->clear_retrain_link) {
- /*
- * Due to an erratum in some devices the Retrain Link bit
- * needs to be cleared again manually to allow the link
- * training to succeed.
- */
- lnkctl &= ~PCI_EXP_LNKCTL_RL;
- pcie_capability_write_word(pdev, PCI_EXP_LNKCTL, lnkctl);
- }
-
- return pcie_wait_for_link_status(pdev, use_lt, !use_lt);
-}
-
/*
* Find maximum D3cold delay required by all the devices on the bus. The
* spec says 100 ms, but firmware can lower it and we allow drivers to
diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index 016a9d4a61f7..f547db0a728f 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -1526,6 +1526,7 @@ void set_pcie_port_type(struct pci_dev *pdev)
{
int pos;
u16 reg16;
+ u32 reg32;
int type;
struct pci_dev *parent;

@@ -1539,6 +1540,10 @@ void set_pcie_port_type(struct pci_dev *pdev)
pci_read_config_dword(pdev, pos + PCI_EXP_DEVCAP, &pdev->devcap);
pdev->pcie_mpss = FIELD_GET(PCI_EXP_DEVCAP_PAYLOAD, pdev->devcap);

+ pcie_capability_read_dword(pdev, PCI_EXP_LNKCAP, &reg32);
+ if (reg32 & PCI_EXP_LNKCAP_DLLLARC)
+ pdev->link_active_reporting = 1;
+
parent = pci_upstream_bridge(pdev);
if (!parent)
return;
@@ -1828,7 +1833,6 @@ int pci_setup_device(struct pci_dev *dev)
int err, pos = 0;
struct pci_bus_region region;
struct resource *res;
- u32 linkcap;

hdr_type = pci_hdr_type(dev);

@@ -1876,10 +1880,6 @@ int pci_setup_device(struct pci_dev *dev)
/* "Unknown power state" */
dev->current_state = PCI_UNKNOWN;

- /* Set it early to make it available to fixups, etc. */
- pcie_capability_read_dword(dev, PCI_EXP_LNKCAP, &linkcap);
- dev->link_active_reporting = !!(linkcap & PCI_EXP_LNKCAP_DLLLARC);
-
/* Early fixups, before probing the BARs */
pci_fixup_device(pci_fixup_early, dev);