linux-kernel - [PATCH] PCI: mediatek-gen3: fix PCIe #PERST being de-asserted too early

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Message-ID: <ZR-7Nm2c5s4kuOp0@pidgin.makrotopia.org>
Date:   Fri, 6 Oct 2023 09:45:58 +0200
From:   Daniel Golle <daniel@...rotopia.org>
To:     linux-pci@...r.kernel.org, linux-mediatek@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Rob Herring <robh@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Jianjun Wang <jianjun.wang@...iatek.com>,
        Ryder Lee <ryder.lee@...iatek.com>
Cc:     Christian Marangi <ansuelsmth@...il.com>,
        Frank Wunderlich <linux@...web.de>,
        John Crispin <john@...ozen.org>
Subject: [PATCH] PCI: mediatek-gen3: fix PCIe #PERST being de-asserted too
 early

The driver for MediaTek gen3 PCIe hosts de-asserts all reset
signals at the same time using a single register write operation.
Delay the de-assertion of the #PERST signal by 100ms as required by
PCIe CEM clause 2.2, some PCIe devices fail to come up otherwise.

Signed-off-by: Daniel Golle <daniel@...rotopia.org>
---
 drivers/pci/controller/pcie-mediatek-gen3.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/controller/pcie-mediatek-gen3.c b/drivers/pci/controller/pcie-mediatek-gen3.c
index e0e27645fdf4..ba8cfce03aad 100644
--- a/drivers/pci/controller/pcie-mediatek-gen3.c
+++ b/drivers/pci/controller/pcie-mediatek-gen3.c
@@ -350,7 +350,13 @@ static int mtk_pcie_startup_port(struct mtk_gen3_pcie *pcie)
 	msleep(100);
 
 	/* De-assert reset signals */
-	val &= ~(PCIE_MAC_RSTB | PCIE_PHY_RSTB | PCIE_BRG_RSTB | PCIE_PE_RSTB);
+	val &= ~(PCIE_MAC_RSTB | PCIE_PHY_RSTB | PCIE_BRG_RSTB);
+	writel_relaxed(val, pcie->base + PCIE_RST_CTRL_REG);
+
+	msleep(100);
+
+	/* De-assert PERST# signals */
+	val &= ~(PCIE_PE_RSTB);
 	writel_relaxed(val, pcie->base + PCIE_RST_CTRL_REG);
 
 	/* Check if the link is up or not */
-- 
2.42.0