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

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Date:   Fri, 8 Jan 2021 00:12:51 +0100
From:   Hauke Mehrtens <hauke@...ke-m.de>
To:     Mathias Kresin <dev@...sin.me>,
        Kishon Vijay Abraham I <kishon@...com>,
        Vinod Koul <vkoul@...nel.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        linux-kernel@...r.kernel.org
Cc:     Martin Blumenstingl <martin.blumenstingl@...glemail.com>,
        stable@...r.kernel.org
Subject: Re: [PATCH] phy: lantiq: rcu-usb2: wait after clock enable

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: <stable@...r.kernel.org> # v5.7+
> Signed-off-by: Mathias Kresin <dev@...sin.me>

Acked-by: Hauke Mehrtens <hauke@...ke-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;
>   }
>