Revert "PCI: dwc: Wait for link up only if link is started"

This reverts commit da56a1b.

Bjorn Andersson, Fabio Estevam, Xiaolei Wang, and Jon Hunter reported that
da56a1b ("PCI: dwc: Wait for link up only if link is started") broke
controller probing by returning an error in case the link does not come up
during host initialisation, for example when the slot is empty.

As explained in commit 886a9c1 ("PCI: dwc: Move link handling into
common code") and as indicated by the comment "Ignore errors, the link may
come up later" in the code, waiting for link up and ignoring errors is the
intended behaviour:

  Let's standardize this to succeed as there are usecases where devices
  (and the link) appear later even without hotplug. For example, a
  reconfigured FPGA device.

Reverting the offending commit specifically fixes a regression on Qualcomm
platforms like the Lenovo ThinkPad X13s which no longer reach the
interconnect sync state if a slot does not have a device populated (e.g. an
optional modem).

Note that enabling asynchronous probing by default as was done for Qualcomm
platforms by commit c0e1eb4 ("PCI: qcom: Enable async probe by
default"), should take care of any related boot time concerns.

Finally, note that the intel-gw driver is the only driver currently not
providing a .start_link() callback and instead starts the link in its
.host_init() callback, which may avoid an additional one-second timeout
during probe by making the link-up wait conditional. If anyone cares, that
can be done in a follow-up patch with a proper motivation.

[bhelgaas: add Fabio Estevam, Xiaolei Wang, Jon Hunter reports]
Fixes: da56a1b ("PCI: dwc: Wait for link up only if link is started")
Link: https://lore.kernel.org/r/[email protected]
Reported-by: Bjorn Andersson <[email protected]>
Signed-off-by: Johan Hovold <[email protected]>
Reported-by: Fabio Estevam <[email protected]>
Link: https://lore.kernel.org/r/[email protected]/
Reported-by: Xiaolei Wang <[email protected]>
Link: https://lore.kernel.org/r/[email protected]/
Reported-by: Jon Hunter <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Bjorn Helgaas <[email protected]>
Reviewed-by: Manivannan Sadhasivam <[email protected]>
Cc: Sajid Dalvi <[email protected]>
Cc: Ajay Agarwal <[email protected]>

Author: jhovold

drivers/pci/controller/dwc/pcie-designware-host.c

@@ -485,20 +485,15 @@ int dw_pcie_host_init(struct dw_pcie_rp *pp)
 	if (ret)
 		goto err_remove_edma;
 
-	if (dw_pcie_link_up(pci)) {
-		dw_pcie_print_link_status(pci);
-	} else {
+	if (!dw_pcie_link_up(pci)) {
 		ret = dw_pcie_start_link(pci);
 		if (ret)
 			goto err_remove_edma;
-
-		if (pci->ops && pci->ops->start_link) {
-			ret = dw_pcie_wait_for_link(pci);
-			if (ret)
-				goto err_stop_link;
-		}
 	}
 
+	/* Ignore errors, the link may come up later */
+	dw_pcie_wait_for_link(pci);
+
 	bridge->sysdata = pp;
 
 	ret = pci_host_probe(bridge);

drivers/pci/controller/dwc/pcie-designware.c

@@ -644,20 +644,9 @@ void dw_pcie_disable_atu(struct dw_pcie *pci, u32 dir, int index)
 	dw_pcie_writel_atu(pci, dir, index, PCIE_ATU_REGION_CTRL2, 0);
 }
 
-void dw_pcie_print_link_status(struct dw_pcie *pci)
-{
-	u32 offset, val;
-
-	offset = dw_pcie_find_capability(pci, PCI_CAP_ID_EXP);
-	val = dw_pcie_readw_dbi(pci, offset + PCI_EXP_LNKSTA);
-
-	dev_info(pci->dev, "PCIe Gen.%u x%u link up\n",
-		 FIELD_GET(PCI_EXP_LNKSTA_CLS, val),
-		 FIELD_GET(PCI_EXP_LNKSTA_NLW, val));
-}
-
 int dw_pcie_wait_for_link(struct dw_pcie *pci)
 {
+	u32 offset, val;
 	int retries;
 
 	/* Check if the link is up or not */
@@ -673,7 +662,12 @@ int dw_pcie_wait_for_link(struct dw_pcie *pci)
 		return -ETIMEDOUT;
 	}
 
-	dw_pcie_print_link_status(pci);
+	offset = dw_pcie_find_capability(pci, PCI_CAP_ID_EXP);
+	val = dw_pcie_readw_dbi(pci, offset + PCI_EXP_LNKSTA);
+
+	dev_info(pci->dev, "PCIe Gen.%u x%u link up\n",
+		 FIELD_GET(PCI_EXP_LNKSTA_CLS, val),
+		 FIELD_GET(PCI_EXP_LNKSTA_NLW, val));
 
 	return 0;
 }

drivers/pci/controller/dwc/pcie-designware.h

@@ -429,7 +429,6 @@ void dw_pcie_setup(struct dw_pcie *pci);
 void dw_pcie_iatu_detect(struct dw_pcie *pci);
 int dw_pcie_edma_detect(struct dw_pcie *pci);
 void dw_pcie_edma_remove(struct dw_pcie *pci);
-void dw_pcie_print_link_status(struct dw_pcie *pci);
 
 static inline void dw_pcie_writel_dbi(struct dw_pcie *pci, u32 reg, u32 val)
 {