[PATCH v2] PCI: dw-rockchip: Delay link training after hot reset in EP mode

From: Niklas Cassel <cassel@kernel.org>
To: "Lorenzo Pieralisi" <lpieralisi@kernel.org>,
	"Krzysztof Wilczyński" <kwilczynski@kernel.org>,
	"Manivannan Sadhasivam" <mani@kernel.org>,
	"Rob Herring" <robh@kernel.org>,
	"Bjorn Helgaas" <bhelgaas@google.com>,
	"Heiko Stuebner" <heiko@sntech.de>
Cc: Wilfred Mallawa <wilfred.mallawa@wdc.com>,
	Niklas Cassel <cassel@kernel.org>,
	linux-pci@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
	linux-rockchip@lists.infradead.org
Subject: [PATCH v2] PCI: dw-rockchip: Delay link training after hot reset in EP mode
Date: Fri, 13 Jun 2025 12:19:09 +0200	[thread overview]
Message-ID: <20250613101908.2182053-2-cassel@kernel.org> (raw)

From: Wilfred Mallawa <wilfred.mallawa@wdc.com>

RK3588 TRM, section "11.6.1.3.3 Hot Reset and Link-Down Reset" states that:
"""
If you want to delay link re-establishment (after reset) so that you can
reprogram some registers through DBI, you must set app_ltssm_enable =0
immediately after core_rst_n as shown in above. This can be achieved by
enable the app_dly2_en, and end-up the delay by assert app_dly2_done.
"""

I.e. setting app_dly2_en will automatically deassert app_ltssm_enable on
a hot reset, and setting app_dly2_done will re-assert app_ltssm_enable,
re-enabling link training.

When receiving a hot reset/link-down IRQ when running in EP mode, we will
call dw_pcie_ep_linkdown(), which will call the .link_down() callback in
the currently bound endpoint function (EPF) drivers.

The callback in an EPF driver can theoretically take a long time to
complete, so make sure that the link is not re-established until after
dw_pcie_ep_linkdown() (which calls the .link_down() callback(s)
synchronously).

Signed-off-by: Wilfred Mallawa <wilfred.mallawa@wdc.com>
Co-developed-by: Niklas Cassel <cassel@kernel.org>
Signed-off-by: Niklas Cassel <cassel@kernel.org>
---
Changes since v1:
-Rebased on v6.16-rc1

 drivers/pci/controller/dwc/pcie-dw-rockchip.c | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/drivers/pci/controller/dwc/pcie-dw-rockchip.c b/drivers/pci/controller/dwc/pcie-dw-rockchip.c
index 93171a392879..cd1e9352b21f 100644
--- a/drivers/pci/controller/dwc/pcie-dw-rockchip.c
+++ b/drivers/pci/controller/dwc/pcie-dw-rockchip.c
@@ -58,6 +58,8 @@
 
 /* Hot Reset Control Register */
 #define PCIE_CLIENT_HOT_RESET_CTRL	0x180
+#define  PCIE_LTSSM_APP_DLY2_EN		BIT(1)
+#define  PCIE_LTSSM_APP_DLY2_DONE	BIT(3)
 #define  PCIE_LTSSM_ENABLE_ENHANCE	BIT(4)
 
 /* LTSSM Status Register */
@@ -474,7 +476,7 @@ static irqreturn_t rockchip_pcie_ep_sys_irq_thread(int irq, void *arg)
 	struct rockchip_pcie *rockchip = arg;
 	struct dw_pcie *pci = &rockchip->pci;
 	struct device *dev = pci->dev;
-	u32 reg;
+	u32 reg, val;
 
 	reg = rockchip_pcie_readl_apb(rockchip, PCIE_CLIENT_INTR_STATUS_MISC);
 	rockchip_pcie_writel_apb(rockchip, reg, PCIE_CLIENT_INTR_STATUS_MISC);
@@ -485,6 +487,10 @@ static irqreturn_t rockchip_pcie_ep_sys_irq_thread(int irq, void *arg)
 	if (reg & PCIE_LINK_REQ_RST_NOT_INT) {
 		dev_dbg(dev, "hot reset or link-down reset\n");
 		dw_pcie_ep_linkdown(&pci->ep);
+		/* Stop delaying link training. */
+		val = HIWORD_UPDATE_BIT(PCIE_LTSSM_APP_DLY2_DONE);
+		rockchip_pcie_writel_apb(rockchip, val,
+					 PCIE_CLIENT_HOT_RESET_CTRL);
 	}
 
 	if (reg & PCIE_RDLH_LINK_UP_CHGED) {
@@ -566,8 +572,11 @@ static int rockchip_pcie_configure_ep(struct platform_device *pdev,
 		return ret;
 	}
 
-	/* LTSSM enable control mode */
-	val = HIWORD_UPDATE_BIT(PCIE_LTSSM_ENABLE_ENHANCE);
+	/*
+	 * LTSSM enable control mode, and automatically delay link training on
+	 * hot reset/link-down reset.
+	 */
+	val = HIWORD_UPDATE_BIT(PCIE_LTSSM_ENABLE_ENHANCE | PCIE_LTSSM_APP_DLY2_EN);
 	rockchip_pcie_writel_apb(rockchip, val, PCIE_CLIENT_HOT_RESET_CTRL);
 
 	rockchip_pcie_writel_apb(rockchip, PCIE_CLIENT_EP_MODE,
-- 
2.49.0


