[PATCH v1 2/6] usb: dwc3-generic: fix ref clock lookup indexing wrong clk_bulk array

[Stefan Eichenberger <eichest@gmail.com>]

From: Stefan Eichenberger <stefan.eichenberger@toradex.com>

On Verdin iMX95, with a USB hub permanently attached to the DWC3 host
port the hub itself enumerates fine but a USB stick plugged into it
fails intermittently:

  Verdin iMX95 # usb start
  starting USB...
  USB XHCI 1.10
  Device not responding to set address.

        USB device not accepting new address (error=80000000)
  Bus usb@4c100000: 2 USB Device(s) found
         scanning usb for storage devices... 0 Storage Device(s) found
  Verdin iMX95 # usb reset
  resetting USB...
  USB XHCI 1.10
  WARN endpoint is halted
  WARN endpoint is halted
  unable to get device descriptor (error=-22)

Commit c6583354b7c1 ("usb: dwc3: Look up reference clock DT phandle in
both controller DT nodes") added a fallback that searches the DWC3
child node's "clock-names" for "ref"/"ref_clk" when it isn't found on
the parent glue node, but always resolves the found index against
glue->clks, a clk_bulk populated only from the parent glue node's own
clock-names list. This is wrong since the child node's clock-names list
is not guaranteed to be in the same order as the parent's, and indeed on
Verdin iMX95 the child node has a different order than the parent node.

Fix it by resolving the index against the child node's clk and ensure to
enable the clock before using it.

Fixes: c6583354b7c1 ("usb: dwc3: Look up reference clock DT phandle in both controller DT nodes")
Signed-off-by: Stefan Eichenberger <stefan.eichenberger@toradex.com>
---
 drivers/usb/dwc3/dwc3-generic.c | 24 ++++++++++++++++++++++--
 1 file changed, 22 insertions(+), 2 deletions(-)

diff --git a/drivers/usb/dwc3/dwc3-generic.c b/drivers/usb/dwc3/dwc3-generic.c
index 2356b3bc0aa..e16d236bd9d 100644
--- a/drivers/usb/dwc3/dwc3-generic.c
+++ b/drivers/usb/dwc3/dwc3-generic.c
@@ -31,6 +31,7 @@ struct dwc3_generic_priv {
 	struct dwc3 dwc3;
 	struct phy_bulk phys;
 	struct gpio_desc *ulpi_reset;
+	struct clk ref_clk;
 };
 
 struct dwc3_generic_host_priv {
@@ -76,9 +77,28 @@ static int dwc3_generic_probe(struct udevice *dev,
 		index = ofnode_stringlist_search(node, "clock-names", "ref");
 		if (index < 0)
 			index = ofnode_stringlist_search(node, "clock-names", "ref_clk");
-	}
-	if (index >= 0)
+		/*
+		 * glue->clks was populated from the parent glue node's own
+		 * clock-names list, which can differ in length/order from
+		 * this child node's list (e.g. i.MX95: glue has "hsio",
+		 * "suspend", the dwc3 child has "bus_early", "ref",
+		 * "suspend"). Reusing this index against glue->clks would
+		 * silently resolve to the wrong clock, so fetch it directly
+		 * from this node instead.
+		 */
+		if (index >= 0) {
+			if (!clk_get_by_index(dev, index, &priv->ref_clk)) {
+				clk_enable(&priv->ref_clk);
+				dwc3->ref_clk = &priv->ref_clk;
+			} else {
+				debug("%s: failed to get ref_clk from DT\n", dev->name);
+			}
+		} else {
+			debug("%s: no ref_clk found in DT\n", dev->name);
+		}
+	} else {
 		dwc3->ref_clk = &glue->clks.clks[index];
+	}
 #endif
 
 	/*
-- 
2.55.0