[RFC][PATCH] PCI: rcar-gen4: Add missing PM ops

[Marek Vasut <marek.vasut+renesas@mailbox.org>]

The R-Car Gen4 PCIe controller is part of a power domain. On R-Car S4
and V4H, this is an always-on power domain which is not shut down in
suspend. On R-Car V4M, this is a dedicated A2PCIPHY power domain,
which is shut down during suspend, and the controller loses state,
which prevents the PCIe from working after resume.

Fix this by adding generic suspend/resume noirq ops for the controller,
which tear the link down on suspend, and restart it on resume. Use the
same PM ops on all of R-Car Gen4 to gracefully suspend and resume the
PCIe link on V4H and S4 too.

Test case which demonstrates the problem on R-Car V4M:
"
$ hexdump -vC /sys/bus/pci/devices/0000:00:00.0/config > /tmp/pre
$ echo s2idle > /sys/power/mem_sleep
$ echo platform > /sys/power/pm_test
$ echo mem > /sys/power/state
$ hexdump -vC /sys/bus/pci/devices/0000:00:00.0/config > /tmp/post
$ diff -Naru /tmp/pre /tmp/post
...
-00000000  12 19 32 00 07 05 10 00  00 00 04 06 00 00 01 00
+00000000  12 19 32 00 07 05 10 00  00 00 00 ff 00 00 80 00
                                          ^^^^^
                                    Class 0604->00ff
"

Fixes: 0d0c551011df ("PCI: rcar-gen4: Add R-Car Gen4 PCIe controller support for host mode")
Reported-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>
---
Cc: "Krzysztof Wilczyński" <kwilczynski@kernel.org>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: Conor Dooley <conor+dt@kernel.org>
Cc: Geert Uytterhoeven <geert+renesas@glider.be>
Cc: Koichiro Den <den@valinux.co.jp>
Cc: Krzysztof Kozlowski <krzk+dt@kernel.org>
Cc: Lorenzo Pieralisi <lpieralisi@kernel.org>
Cc: Magnus Damm <magnus.damm@gmail.com>
Cc: Manivannan Sadhasivam <mani@kernel.org>
Cc: Rob Herring <robh@kernel.org>
Cc: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Cc: devicetree@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: linux-pci@vger.kernel.org
Cc: linux-renesas-soc@vger.kernel.org
---
NOTE: Depends on series
      https://lore.kernel.org/linux-pci/20260903205153.283553-1-marek.vasut+renesas@mailbox.org/
NOTE: I am sending this as an RFC, because I would like to get
      a TB from Geert before this might get applied
---
 drivers/pci/controller/dwc/pcie-rcar-gen4.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/drivers/pci/controller/dwc/pcie-rcar-gen4.c b/drivers/pci/controller/dwc/pcie-rcar-gen4.c
index 5690dc32f47e0..3bfb2bd53fe3b 100644
--- a/drivers/pci/controller/dwc/pcie-rcar-gen4.c
+++ b/drivers/pci/controller/dwc/pcie-rcar-gen4.c
@@ -909,6 +909,22 @@ static int rcar_gen4_pcie_ltssm_control(struct rcar_gen4_pcie *rcar, bool enable
 	return 0;
 }
 
+static int rcar_gen4_pcie_suspend_noirq(struct device *dev)
+{
+	struct rcar_gen4_pcie *rcar = dev_get_drvdata(dev);
+	struct dw_pcie *dw = &rcar->dw;
+
+	return dw_pcie_suspend_noirq(dw);
+}
+
+static int rcar_gen4_pcie_resume_noirq(struct device *dev)
+{
+	struct rcar_gen4_pcie *rcar = dev_get_drvdata(dev);
+	struct dw_pcie *dw = &rcar->dw;
+
+	return dw_pcie_resume_noirq(dw);
+}
+
 static struct rcar_gen4_pcie_drvdata drvdata_r8a779f0_pcie = {
 	.ltssm_control = r8a779f0_pcie_ltssm_control,
 	.mode = DW_PCIE_RC_TYPE,
@@ -952,10 +968,14 @@ static const struct of_device_id rcar_gen4_pcie_of_match[] = {
 };
 MODULE_DEVICE_TABLE(of, rcar_gen4_pcie_of_match);
 
+DEFINE_NOIRQ_DEV_PM_OPS(rcar_gen4_pcie_pm_ops,
+			rcar_gen4_pcie_suspend_noirq, rcar_gen4_pcie_resume_noirq);
+
 static struct platform_driver rcar_gen4_pcie_driver = {
 	.driver = {
 		.name = "pcie-rcar-gen4",
 		.of_match_table = rcar_gen4_pcie_of_match,
+		.pm = &rcar_gen4_pcie_pm_ops,
 		.probe_type = PROBE_PREFER_ASYNCHRONOUS,
 	},
 	.probe = rcar_gen4_pcie_probe,
-- 
2.53.0