PCI: mediatek-gen3: Assert resets to ensure expected init state

[ Upstream commit 1d56593 ]

The controller may have been left out of reset by the bootloader,
in which case, before the powerup sequence, the controller will be
found preconfigured with values that were set before booting the
kernel: this produces a controller failure, with the result of
a failure during the mtk_pcie_startup_port() sequence as the PCIe
link never gets up.

To ensure that we get a clean start in an expected state, assert
both the PHY and MAC resets before executing the controller
power-up sequence.

Link: https://lore.kernel.org/r/20220404144858.92390-1-angelogioacchino.delregno@collabora.com
Fixes: d3bf75b ("PCI: mediatek-gen3: Add MediaTek Gen3 driver for MT8192")
Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

drivers/pci/controller/pcie-mediatek-gen3.c

@@ -838,6 +838,14 @@ static int mtk_pcie_setup(struct mtk_gen3_pcie *pcie)
 	if (err)
 		return err;
 
+	/*
+	 * The controller may have been left out of reset by the bootloader
+	 * so make sure that we get a clean start by asserting resets here.
+	 */
+	reset_control_assert(pcie->phy_reset);
+	reset_control_assert(pcie->mac_reset);
+	usleep_range(10, 20);
+
 	/* Don't touch the hardware registers before power up */
 	err = mtk_pcie_power_up(pcie);
 	if (err)