PCI: rockchip: Advertise 128-byte Read Completion Boundary support

Rockchip Root Ports support either 64 or 128 byte Read Completion Boundary
(RCB).  Set the RCB bit in the Link Control register to indicate this.

A 128 byte RCB significantly improves performance of NVMe with libaio.

[bhelgaas: changelog]
Signed-off-by: NShawn Lin <shawn.lin@rock-chips.com>
Signed-off-by: NBjorn Helgaas <bhelgaas@google.com>
Cc: Brian Norris <briannorris@chromium.org>
Cc: Jeffy Chen <jeffy.chen@rock-chips.com>

drivers/pci/host/pcie-rockchip.c

@@ -601,6 +601,11 @@ static int rockchip_pcie_init_port(struct rockchip_pcie *rockchip)
 	status |= PCI_EXP_LNKCTL_CCC;
 	rockchip_pcie_write(rockchip, status, PCIE_RC_CONFIG_LCS);
 
+	/* Set RC's RCB to 128 */
+	status = rockchip_pcie_read(rockchip, PCIE_RC_CONFIG_LCS);
+	status |= PCI_EXP_LNKCTL_RCB;
+	rockchip_pcie_write(rockchip, status, PCIE_RC_CONFIG_LCS);
+
 	/* Enable Gen1 training */
 	rockchip_pcie_write(rockchip, PCIE_CLIENT_LINK_TRAIN_ENABLE,
 			    PCIE_CLIENT_CONFIG);