Re: [PATCH] phy: lantiq: rcu-usb2: wait after clock enable

[Hauke Mehrtens]

On 1/7/21 11:49 PM, Mathias Kresin wrote:
Commit 65dc2e725286 ("usb: dwc2: Update Core Reset programming flow.")
revealed that the phy isn't ready immediately after enabling it's
clocks. The dwc2_check_core_version() fails and the dwc2 usb driver
errors out.
Add a short delay to let the phy get up and running. There isn't any
documentation how much time is required, the value was chosen based on
tests.

Cc: <sta...@vger.kernel.org> # v5.7+
Signed-off-by: Mathias Kresin <d...@kresin.me>

Acked-by: Hauke Mehrtens <ha...@hauke-m.de>

I do not know how long you have to wait here, but this looks ok, when it 
works.

Hauke

---
  drivers/phy/lantiq/phy-lantiq-rcu-usb2.c | 10 +++++++++-
  1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/drivers/phy/lantiq/phy-lantiq-rcu-usb2.c 
b/drivers/phy/lantiq/phy-lantiq-rcu-usb2.c
index a7d126192cf1..29d246ea24b4 100644
--- a/drivers/phy/lantiq/phy-lantiq-rcu-usb2.c
+++ b/drivers/phy/lantiq/phy-lantiq-rcu-usb2.c
@@ -124,8 +124,16 @@ static int ltq_rcu_usb2_phy_power_on(struct phy *phy)
        reset_control_deassert(priv->phy_reset);
  
  	ret = clk_prepare_enable(priv->phy_gate_clk);
-       if (ret)
+       if (ret) {
                dev_err(dev, "failed to enable PHY gate\n");
+               return ret;
+       }
+
+       /*
+        * at least the xrx200 usb2 phy requires some extra time to be
+        * operational after enabling the clock
+        */
+       usleep_range(100, 200);
  
  	return ret;
  }