linux-kernel - [PATCH v1 1/3] PCI: mediatek-gen3: Implement sys clock ready time setting

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Message-ID: <20250623120058.109036-2-angelogioacchino.delregno@collabora.com>
Date: Mon, 23 Jun 2025 14:00:56 +0200
From: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
To: jianjun.wang@...iatek.com
Cc: ryder.lee@...iatek.com,
	bhelgaas@...gle.com,
	lpieralisi@...nel.org,
	kwilczynski@...nel.org,
	manivannan.sadhasivam@...aro.org,
	robh@...nel.org,
	krzk+dt@...nel.org,
	conor+dt@...nel.org,
	matthias.bgg@...il.com,
	angelogioacchino.delregno@...labora.com,
	linux-pci@...r.kernel.org,
	linux-mediatek@...ts.infradead.org,
	devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	kernel@...labora.com
Subject: [PATCH v1 1/3] PCI: mediatek-gen3: Implement sys clock ready time setting

In preparation to add support for the PCI-Express Gen3 controller
found in newer MediaTek SoCs, such as the Dimensity 9400 MT6991
and the MT8196 Chromebook SoC, add the definition for the PCIE
Resource Control register and a new sys_clk_rdy_time_us variable
in platform data.

If sys_clk_rdy_time_us is found (> 0), set the new value in the
aforementioned register only after configuring the controller to
RC mode, as this may otherwise be reset.

Overriding the register defaults for SYS_CLK_RDY_TIME allows to
work around sys_clk_rdy signal glitching in MT6991 and MT8196.

Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
---
 drivers/pci/controller/pcie-mediatek-gen3.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/drivers/pci/controller/pcie-mediatek-gen3.c b/drivers/pci/controller/pcie-mediatek-gen3.c
index b55f5973414c..00c9f2532870 100644
--- a/drivers/pci/controller/pcie-mediatek-gen3.c
+++ b/drivers/pci/controller/pcie-mediatek-gen3.c
@@ -101,6 +101,9 @@
 #define PCIE_MSI_SET_ADDR_HI_BASE	0xc80
 #define PCIE_MSI_SET_ADDR_HI_OFFSET	0x04
 
+#define PCIE_RESOURCE_CTRL_REG		0xd2c
+#define PCIE_RSRC_SYS_CLK_RDY_TIME_MASK	GENMASK(7, 0)
+
 #define PCIE_ICMD_PM_REG		0x198
 #define PCIE_TURN_OFF_LINK		BIT(4)
 
@@ -148,6 +151,7 @@ enum mtk_gen3_pcie_flags {
  * struct mtk_gen3_pcie_pdata - differentiate between host generations
  * @power_up: pcie power_up callback
  * @phy_resets: phy reset lines SoC data.
+ * @sys_clk_rdy_time_us: System clock ready time override (microseconds)
  * @flags: pcie device flags.
  */
 struct mtk_gen3_pcie_pdata {
@@ -156,6 +160,7 @@ struct mtk_gen3_pcie_pdata {
 		const char *id[MAX_NUM_PHY_RESETS];
 		int num_resets;
 	} phy_resets;
+	u8 sys_clk_rdy_time_us;
 	u32 flags;
 };
 
@@ -436,6 +441,15 @@ static int mtk_pcie_startup_port(struct mtk_gen3_pcie *pcie)
 		writel_relaxed(val, pcie->base + PCIE_CONF_LINK2_CTL_STS);
 	}
 
+	/* If parameter is present, adjust SYS_CLK_RDY_TIME to avoid glitching */
+	if (pcie->soc->sys_clk_rdy_time_us) {
+		val = readl_relaxed(pcie->base + PCIE_RESOURCE_CTRL_REG);
+		val &= ~PCIE_RSRC_SYS_CLK_RDY_TIME_MASK;
+		val |= FIELD_PREP(PCIE_RSRC_SYS_CLK_RDY_TIME_MASK,
+				  pcie->soc->sys_clk_rdy_time_us);
+		writel_relaxed(val, pcie->base + PCIE_RESOURCE_CTRL_REG);
+	}
+
 	/* Set class code */
 	val = readl_relaxed(pcie->base + PCIE_PCI_IDS_1);
 	val &= ~GENMASK(31, 8);
-- 
2.49.0