linux-kernel - Re: [PATCH 1/2] usb: misc: onboard_usb

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Date:   Thu, 23 Nov 2023 13:55:57 +0000
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Frieder Schrempf <frieder@...s.de>
Cc:     linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
        Matthias Kaehlcke <mka@...omium.org>,
        Frieder Schrempf <frieder.schrempf@...tron.de>,
        Anand Moon <linux.amoon@...il.com>,
        Benjamin Bara <benjamin.bara@...data.com>,
        Icenowy Zheng <uwu@...nowy.me>, Rob Herring <robh@...nel.org>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
Subject: Re: [PATCH 1/2] usb: misc: onboard_usb_hub: Add support for clock
 input

On Thu, Nov 23, 2023 at 02:47:20PM +0100, Frieder Schrempf wrote:
> From: Frieder Schrempf <frieder.schrempf@...tron.de>
> 
> Most onboard USB hubs have a dedicated crystal oscillator but on some
> boards the clock signal for the hub is provided by the SoC.
> 
> In order to support this, we add the possibility of specifying a
> clock in the devicetree that gets enabled/disabled when the hub
> is powered up/down.
> 
> Signed-off-by: Frieder Schrempf <frieder.schrempf@...tron.de>
> ---
>  drivers/usb/misc/onboard_usb_hub.c | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
> 
> diff --git a/drivers/usb/misc/onboard_usb_hub.c b/drivers/usb/misc/onboard_usb_hub.c
> index a341b2fbb7b44..e710e3c82ba9b 100644
> --- a/drivers/usb/misc/onboard_usb_hub.c
> +++ b/drivers/usb/misc/onboard_usb_hub.c
> @@ -5,6 +5,7 @@
>   * Copyright (c) 2022, Google LLC
>   */
>  
> +#include <linux/clk.h>
>  #include <linux/device.h>
>  #include <linux/export.h>
>  #include <linux/gpio/consumer.h>
> @@ -60,12 +61,19 @@ struct onboard_hub {
>  	bool going_away;
>  	struct list_head udev_list;
>  	struct mutex lock;
> +	struct clk *clk;
>  };
>  
>  static int onboard_hub_power_on(struct onboard_hub *hub)
>  {
>  	int err;
>  
> +	err = clk_prepare_enable(hub->clk);
> +	if (err) {
> +		dev_err(hub->dev, "failed to enable clock: %d\n", err);
> +		return err;
> +	}

But what happens if clk is not set here?

And doesn't clk_prepare_enable() print out a message if it fails?

thanks,

greg k-h