[PATCH v2 1/4] PCI: dw-rockchip: Do not enumerate bus before endpoint devices are ready

[Niklas Cassel <cassel@kernel.org>]

Commit ec9fd499b9c6 ("PCI: dw-rockchip: Don't wait for link since 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.

Laszlo Fiat reported (off-list) that his PLEXTOR PX-256M8PeGN NVMe SSD is
no longer functional, and simply reverting commit ec9fd499b9c6 ("PCI:
dw-rockchip: Don't wait for link since we can detect Link Up") makes his
SSD functional again.

It seems that we are enumerating the bus before the endpoint is ready.
Adding a msleep(PCIE_T_RRS_READY_MS) before enumerating the bus in the
threaded IRQ handler makes the SSD functional once again.

What appears to happen is that before ec9fd499b9c6, 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,
that would essentially bring back an unconditional delay during synchronous
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, we will not have an unconditional delay during boot
for unpopulated PCIe slots.

Cc: Laszlo Fiat <laszlo.fiat@proton.me>
Fixes: ec9fd499b9c6 ("PCI: dw-rockchip: Don't wait for link since we can detect Link Up")
Signed-off-by: Niklas Cassel <cassel@kernel.org>
---
 drivers/pci/controller/dwc/pcie-dw-rockchip.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/pci/controller/dwc/pcie-dw-rockchip.c b/drivers/pci/controller/dwc/pcie-dw-rockchip.c
index 3c6ab71c996e..6a7ec3545a7f 100644
--- a/drivers/pci/controller/dwc/pcie-dw-rockchip.c
+++ b/drivers/pci/controller/dwc/pcie-dw-rockchip.c
@@ -23,6 +23,7 @@
 #include <linux/reset.h>
 
 #include "pcie-designware.h"
+#include "../../pci.h"
 
 /*
  * The upper 16 bits of PCIE_CLIENT_CONFIG are a write
@@ -458,6 +459,7 @@ static irqreturn_t rockchip_pcie_rc_sys_irq_thread(int irq, void *arg)
 	if (reg & PCIE_RDLH_LINK_UP_CHGED) {
 		if (rockchip_pcie_link_up(pci)) {
 			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