phy: starfive: jh7110-usb: Fix link configuration to controller

In order to connect the USB 2.0 PHY to its controller, we also need to
set "u0_pdrstn_split_sw_usbpipe_plugen" [1]. Some downstream U-Boot
versions did that, but upstream firmware does not, and the kernel must
not rely on such behavior anyway. Failing to set this left the USB
gadget port invisible to connected hosts behind.

Link: https://doc-en.rvspace.org/JH7110/TRM/JH7110_TRM/sys_syscon.html#sys_syscon__section_b3l_fqs_wsb [1]
Fixes: 16d3a71 ("phy: starfive: Add JH7110 USB 2.0 PHY driver")
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Minda Chen <minda.chen@starfivetech.com>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20241015070444.20972-2-minda.chen@starfivetech.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>

drivers/phy/starfive/phy-jh7110-usb.c

@@ -10,18 +10,24 @@
 #include <linux/clk.h>
 #include <linux/err.h>
 #include <linux/io.h>
+#include <linux/mfd/syscon.h>
 #include <linux/module.h>
 #include <linux/phy/phy.h>
 #include <linux/platform_device.h>
+#include <linux/regmap.h>
 #include <linux/usb/of.h>
 
 #define USB_125M_CLK_RATE		125000000
 #define USB_LS_KEEPALIVE_OFF		0x4
 #define USB_LS_KEEPALIVE_ENABLE		BIT(4)
 
+#define USB_PDRSTN_SPLIT		BIT(17)
+#define SYSCON_USB_SPLIT_OFFSET		0x18
+
 struct jh7110_usb2_phy {
 	struct phy *phy;
 	void __iomem *regs;
+	struct regmap *sys_syscon;
 	struct clk *usb_125m_clk;
 	struct clk *app_125m;
 	enum phy_mode mode;
@@ -61,6 +67,10 @@ static int usb2_phy_set_mode(struct phy *_phy,
 		usb2_set_ls_keepalive(phy, (mode != PHY_MODE_USB_DEVICE));
 	}
 
+	/* Connect usb 2.0 phy mode */
+	regmap_update_bits(phy->sys_syscon, SYSCON_USB_SPLIT_OFFSET,
+			   USB_PDRSTN_SPLIT, USB_PDRSTN_SPLIT);
+
 	return 0;
 }
 
@@ -129,6 +139,12 @@ static int jh7110_usb_phy_probe(struct platform_device *pdev)
 	phy_set_drvdata(phy->phy, phy);
 	phy_provider = devm_of_phy_provider_register(dev, of_phy_simple_xlate);
 
+	phy->sys_syscon =
+		syscon_regmap_lookup_by_compatible("starfive,jh7110-sys-syscon");
+	if (IS_ERR(phy->sys_syscon))
+		return dev_err_probe(dev, PTR_ERR(phy->sys_syscon),
+				     "Failed to get sys-syscon\n");
+
 	return PTR_ERR_OR_ZERO(phy_provider);
 }