[PATCH v2 2/3] usb: octeon-hcd: fail the probe when the USB core does not respond

[Orgad Shaneh <orgads@gmail.com>]

If the USBN clock/PHY setup did not actually bring the core up (wrong
board reference-clock configuration, for instance), every USBC CSR
reads as all-ones and initialization marches on programming garbage,
ending in timeouts or a wedge deep in the FIFO flush.

Read GHWCFG3 - a hardwired configuration register that can be neither
0 nor all-ones on a live core - right before core initialization, and
give up cleanly if the core is not answering.

Assisted-by: Claude:claude-opus-5
Signed-off-by: Orgad Shaneh <orgads@gmail.com>
---

v2: no code change; added the Assisted-by tag for the AI assistance used
    (Documentation/process/coding-assistants.rst).

diff --git a/drivers/usb/host/octeon-hcd.c b/drivers/usb/host/octeon-hcd.c
--- a/drivers/usb/host/octeon-hcd.c
+++ b/drivers/usb/host/octeon-hcd.c
@@ -853,6 +853,14 @@
 	 *    USBC_GAHBCFG[PTXFEMPLVL]
 	 *    Global interrupt mask, USBC_GAHBCFG[GLBLINTRMSK] = 1
 	 */
+	usbcx_gahbcfg.u32 = cvmx_usb_read_csr32(usb,
+						CVMX_USBCX_GHWCFG3(usb->index));
+	if (usbcx_gahbcfg.u32 == 0xffffffff || usbcx_gahbcfg.u32 == 0) {
+		dev_err(dev, "USB core is not responding (GHWCFG3=0x%08x)\n",
+			usbcx_gahbcfg.u32);
+		return -ENODEV;
+	}
+
 	usbcx_gahbcfg.u32 = 0;
 	usbcx_gahbcfg.s.dmaen = !(usb->init_flags &
 				  CVMX_USB_INITIALIZE_FLAGS_NO_DMA);
-- 
2.47.0