linux-kernel - [RFC 1/2] PCI: imx6: Make sure the DBI register can be changed

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Date:   Wed, 18 May 2022 17:35:27 +0800
From:   Richard Zhu <hongxing.zhu@....com>
To:     l.stach@...gutronix.de, bhelgaas@...gle.com,
        lorenzo.pieralisi@....com, festevam@...il.com
Cc:     hongxing.zhu@....com, linux-pci@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kernel@...gutronix.de, linux-imx@....com
Subject: [RFC 1/2] PCI: imx6: Make sure the DBI register can be changed

The PCIE_DBI_RO_WR_EN bit should be set when write some DBI registers.
To make sure that the DBI registers are writable, set the
PCIE_DBI_RO_WR_EN properly when touch the DBI registers.

Signed-off-by: Richard Zhu <hongxing.zhu@....com>
---
 drivers/pci/controller/dwc/pci-imx6.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/pci/controller/dwc/pci-imx6.c b/drivers/pci/controller/dwc/pci-imx6.c
index 6619e3caffe2..30641d2dda14 100644
--- a/drivers/pci/controller/dwc/pci-imx6.c
+++ b/drivers/pci/controller/dwc/pci-imx6.c
@@ -797,10 +797,12 @@ static int imx6_pcie_start_link(struct dw_pcie *pci)
 	 * started in Gen2 mode, there is a possibility the devices on the
 	 * bus will not be detected at all.  This happens with PCIe switches.
 	 */
+	dw_pcie_dbi_ro_wr_en(pci);
 	tmp = dw_pcie_readl_dbi(pci, offset + PCI_EXP_LNKCAP);
 	tmp &= ~PCI_EXP_LNKCAP_SLS;
 	tmp |= PCI_EXP_LNKCAP_SLS_2_5GB;
 	dw_pcie_writel_dbi(pci, offset + PCI_EXP_LNKCAP, tmp);
+	dw_pcie_dbi_ro_wr_dis(pci);
 
 	/* Start LTSSM. */
 	imx6_pcie_ltssm_enable(dev);
@@ -809,6 +811,7 @@ static int imx6_pcie_start_link(struct dw_pcie *pci)
 
 	if (pci->link_gen == 2) {
 		/* Allow Gen2 mode after the link is up. */
+		dw_pcie_dbi_ro_wr_en(pci);
 		tmp = dw_pcie_readl_dbi(pci, offset + PCI_EXP_LNKCAP);
 		tmp &= ~PCI_EXP_LNKCAP_SLS;
 		tmp |= PCI_EXP_LNKCAP_SLS_5_0GB;
@@ -821,6 +824,7 @@ static int imx6_pcie_start_link(struct dw_pcie *pci)
 		tmp = dw_pcie_readl_dbi(pci, PCIE_LINK_WIDTH_SPEED_CONTROL);
 		tmp |= PORT_LOGIC_SPEED_CHANGE;
 		dw_pcie_writel_dbi(pci, PCIE_LINK_WIDTH_SPEED_CONTROL, tmp);
+		dw_pcie_dbi_ro_wr_dis(pci);
 
 		if (imx6_pcie->drvdata->flags &
 		    IMX6_PCIE_FLAG_IMX6_SPEED_CHANGE) {
-- 
2.25.1