[PATCH 2/4] PCI: qcom: Do not enumerate bus before endpoint devices are ready

[Niklas Cassel <cassel@kernel.org>]

Commit 36971d6c5a9a ("PCI: qcom: Don't wait for link if we can detect Link
Up") changed so that we no longer call dw_pcie_wait_for_link(), and instead
enumerate the bus when receiving a Link Up IRQ.

Before 36971d6c5a9a, we called dw_pcie_wait_for_link(), and in the first
iteration of the loop, the link will never be up (because the link was just
started), dw_pcie_wait_for_link() will then sleep for LINK_WAIT_SLEEP_MS
(90 ms), before trying again.

This means that even if a driver was missing a msleep(PCIE_T_RRS_READY_MS)
(100 ms), because of the call to dw_pcie_wait_for_link(), enumerating the
bus would essentially be delayed by that time anyway (because of the sleep
LINK_WAIT_SLEEP_MS (90 ms)).

While we could add the msleep(PCIE_T_RRS_READY_MS) after deasserting PERST
(qcom already has an unconditional 1 ms sleep after deasserting PERST),
that would essentially bring back an unconditional delay during probe (the
whole reason to use a Link Up IRQ was to avoid an unconditional delay
during probe).

Thus, add the msleep(PCIE_T_RRS_READY_MS) before enumerating the bus in the
IRQ handler. This way, for qcom SoCs that has a link up IRQ, we will not
have a 100 ms unconditional delay during boot for unpopulated PCIe slots.

Fixes: 36971d6c5a9a ("PCI: qcom: Don't wait for link if we can detect Link Up")
Signed-off-by: Niklas Cassel <cassel@kernel.org>
---
 drivers/pci/controller/dwc/pcie-qcom.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/pci/controller/dwc/pcie-qcom.c b/drivers/pci/controller/dwc/pcie-qcom.c
index 6b18a2775e7f..5cef5e92b173 100644
--- a/drivers/pci/controller/dwc/pcie-qcom.c
+++ b/drivers/pci/controller/dwc/pcie-qcom.c
@@ -1646,6 +1646,7 @@ static irqreturn_t qcom_pcie_global_irq_thread(int irq, void *data)
 
 	if (FIELD_GET(PARF_INT_ALL_LINK_UP, status)) {
 		dev_dbg(dev, "Received Link up event. Starting enumeration!\n");
+		msleep(PCIE_T_RRS_READY_MS);
 		/* Rescan the bus to enumerate endpoint devices */
 		pci_lock_rescan_remove();
 		pci_rescan_bus(pp->bridge->bus);
-- 
2.49.0