[PATCH v5 3/4] PCI: rockchip: drive at 2.5 GT/s, error other speeds

[Geraldo Nascimento <geraldogabriel@gmail.com>]

Configure the core to be driven at 2.5 GT/s Link Speed and ignore
any other speed with a warning. The reason is that Shawn Lin from
Rockchip has reiterated that there may be danger of "catastrophic
failure" in using their PCIe with 5.0 GT/s speeds.

While Rockchip has done so informally without issuing a proper errata,
and the particulars are thus unknown, this may cause data loss or
worse.

This change is corroborated by RK3399 official datasheet [1], which
states maximum link speed for this platform is 2.5 GT/s.

[1] https://opensource.rock-chips.com/images/d/d7/Rockchip_RK3399_Datasheet_V2.1-20200323.pdf

Fixes: 956cd99b35a8 ("PCI: rockchip: Separate common code from RC driver")
Link: https://lore.kernel.org/all/ffd05070-9879-4468-94e3-b88968b4c21b@rock-chips.com/
Cc: stable@vger.kernel.org
Reported-by: Dragan Simic <dsimic@manjaro.org>
Reported-by: Shawn Lin <shawn.lin@rock-chips.com>
Signed-off-by: Geraldo Nascimento <geraldogabriel@gmail.com>
---
 drivers/pci/controller/pcie-rockchip.c | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/drivers/pci/controller/pcie-rockchip.c b/drivers/pci/controller/pcie-rockchip.c
index 0f88da378805..2f211d1f4c7c 100644
--- a/drivers/pci/controller/pcie-rockchip.c
+++ b/drivers/pci/controller/pcie-rockchip.c
@@ -66,8 +66,10 @@ int rockchip_pcie_parse_dt(struct rockchip_pcie *rockchip)
 	}
 
 	rockchip->link_gen = of_pci_get_max_link_speed(node);
-	if (rockchip->link_gen < 0 || rockchip->link_gen > 2)
-		rockchip->link_gen = 2;
+	if (rockchip->link_gen < 0 || rockchip->link_gen >= 2) {
+		rockchip->link_gen = 1;
+		dev_warn(dev, "invalid max-link-speed, fix your DT\n");
+	}
 
 	for (i = 0; i < ROCKCHIP_NUM_PM_RSTS; i++)
 		rockchip->pm_rsts[i].id = rockchip_pci_pm_rsts[i];
@@ -147,12 +149,13 @@ int rockchip_pcie_init_port(struct rockchip_pcie *rockchip)
 		goto err_exit_phy;
 	}
 
-	if (rockchip->link_gen == 2)
-		rockchip_pcie_write(rockchip, PCIE_CLIENT_GEN_SEL_2,
-				    PCIE_CLIENT_CONFIG);
-	else
+	if (rockchip->link_gen == 2) {
+		/* 5.0 GT/s may cause catastrophic failure for this core */
+		dev_warn(dev, "5.0 GT/s may cause data loss or worse\n");
+	} else {
 		rockchip_pcie_write(rockchip, PCIE_CLIENT_GEN_SEL_1,
 				    PCIE_CLIENT_CONFIG);
+	}
 
 	regs = PCIE_CLIENT_ARI_ENABLE |
 	       PCIE_CLIENT_CONF_LANE_NUM(rockchip->lanes);
-- 
2.52.0