linux-kernel - [PATCH v3] PCI: mediatek: Assert PERST# for 100ms for power and clock to stabilize

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Date:   Mon, 27 Dec 2021 21:31:10 +0800
From:   qizhong cheng <qizhong.cheng@...iatek.com>
To:     Ryder Lee <ryder.lee@...iatek.com>,
        Jianjun Wang <jianjun.wang@...iatek.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>
CC:     <linux-pci@...r.kernel.org>, <linux-mediatek@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <qizhong.cheng@...iatek.com>, <chuanjia.liu@...iatek.com>,
        Pali Rohár <pali@...nel.org>
Subject: [PATCH v3] PCI: mediatek: Assert PERST# for 100ms for power and clock to stabilize

Described in PCIe CEM specification sections 2.2 (PERST# Signal) and
2.2.1 (Initial Power-Up (G3 to S0)). The deassertion of PERST# should
be delayed 100ms (TPVPERL) for the power and clock to become stable.

Signed-off-by: qizhong cheng <qizhong.cheng@...iatek.com>
Acked-by: Pali Rohár <pali@...nel.org>
---

v3:
 - Change subject.

v2:
 - Typo fix.
 - Rewrap into one paragraph.

 drivers/pci/controller/pcie-mediatek.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/pci/controller/pcie-mediatek.c b/drivers/pci/controller/pcie-mediatek.c
index 2f3f974977a3..b18935e8da89 100644
--- a/drivers/pci/controller/pcie-mediatek.c
+++ b/drivers/pci/controller/pcie-mediatek.c
@@ -702,6 +702,13 @@ static int mtk_pcie_startup_port_v2(struct mtk_pcie_port *port)
 	 */
 	writel(PCIE_LINKDOWN_RST_EN, port->base + PCIE_RST_CTRL);
 
+	/*
+	 * Described in PCIe CEM specification sections 2.2 (PERST# Signal) and
+	 * 2.2.1 (Initial Power-Up (G3 to S0)). The deassertion of PERST# should
+	 * be delayed 100ms (TPVPERL) for the power and clock to become stable.
+	 */
+	msleep(100);
+
 	/* De-assert PHY, PE, PIPE, MAC and configuration reset	*/
 	val = readl(port->base + PCIE_RST_CTRL);
 	val |= PCIE_PHY_RSTB | PCIE_PERSTB | PCIE_PIPE_SRSTB |
-- 
2.25.1