PCI: dwc: Group DBI registers writes requiring unlocking

Some of DesignWare core's DBI registers (a.k.a configuration space
registers) are write-protected with a lock without enabling which they
are read-only by default.

These write-protected registers are implementation specific. Tegra194's
BAR-0 register which is at offset 0x10 in the configuration space is an
example. Current implementation in dw_pcie_setup_rc() API attempts to
unlock those write-protected registers whenever they are updated and
lock them back again for writing.

Group all write-protected registers writes so that locking and unlocking
is performed once to avoid bloating the code with multiple unlock/lock
sequences for all those write-protected registers.

Signed-off-by: Vidya Sagar <vidyas@nvidia.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: Thierry Reding <treding@nvidia.com>
Acked-by: Jingoo Han <jingoohan1@gmail.com>

drivers/pci/controller/dwc/pcie-designware-host.c

@@ -628,6 +628,12 @@ void dw_pcie_setup_rc(struct pcie_port *pp)
 	u32 val, ctrl, num_ctrls;
 	struct dw_pcie *pci = to_dw_pcie_from_pp(pp);
 
+	/*
+	 * Enable DBI read-only registers for writing/updating configuration.
+	 * Write permission gets disabled towards the end of this function.
+	 */
+	dw_pcie_dbi_ro_wr_en(pci);
+
 	dw_pcie_setup(pci);
 
 	if (!pp->ops->msi_host_init) {
@@ -650,12 +656,10 @@ void dw_pcie_setup_rc(struct pcie_port *pp)
 	dw_pcie_writel_dbi(pci, PCI_BASE_ADDRESS_1, 0x00000000);
 
 	/* Setup interrupt pins */
-	dw_pcie_dbi_ro_wr_en(pci);
 	val = dw_pcie_readl_dbi(pci, PCI_INTERRUPT_LINE);
 	val &= 0xffff00ff;
 	val |= 0x00000100;
 	dw_pcie_writel_dbi(pci, PCI_INTERRUPT_LINE, val);
-	dw_pcie_dbi_ro_wr_dis(pci);
 
 	/* Setup bus numbers */
 	val = dw_pcie_readl_dbi(pci, PCI_PRIMARY_BUS);
@@ -687,15 +691,13 @@ void dw_pcie_setup_rc(struct pcie_port *pp)
 
 	dw_pcie_wr_own_conf(pp, PCI_BASE_ADDRESS_0, 4, 0);
 
-	/* Enable write permission for the DBI read-only register */
-	dw_pcie_dbi_ro_wr_en(pci);
 	/* Program correct class for RC */
 	dw_pcie_wr_own_conf(pp, PCI_CLASS_DEVICE, 2, PCI_CLASS_BRIDGE_PCI);
-	/* Better disable write permission right after the update */
-	dw_pcie_dbi_ro_wr_dis(pci);
 
 	dw_pcie_rd_own_conf(pp, PCIE_LINK_WIDTH_SPEED_CONTROL, 4, &val);
 	val |= PORT_LOGIC_SPEED_CHANGE;
 	dw_pcie_wr_own_conf(pp, PCIE_LINK_WIDTH_SPEED_CONTROL, 4, val);
+
+	dw_pcie_dbi_ro_wr_dis(pci);
 }
 EXPORT_SYMBOL_GPL(dw_pcie_setup_rc);