[PATCH v2] usb: gadget: at91_udc: move prepare clk into process context

[Boris BREZILLON]

Hi Ronald,

On Wed,  6 Aug 2014 15:11:42 +0200
Ronald Wahl <ronald.wahl at raritan.com> wrote:

> Commit 7628083227b6bc4a7e33d7c381d7a4e558424b6b added clock preparation in
> interrupt context. This is not allowed as it might sleep. Move clock
> preparation into process context (at91udc_probe).
> ---
>  drivers/usb/gadget/udc/at91_udc.c | 39 ++++++++++++++++++++++++++++++---------
>  1 file changed, 30 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/usb/gadget/udc/at91_udc.c b/drivers/usb/gadget/udc/at91_udc.c
> index cfd18bc..0b347a0 100644
> --- a/drivers/usb/gadget/udc/at91_udc.c
> +++ b/drivers/usb/gadget/udc/at91_udc.c
> @@ -872,10 +872,10 @@ static void clk_on(struct at91_udc *udc)
>  
>  	if (IS_ENABLED(CONFIG_COMMON_CLK)) {
>  		clk_set_rate(udc->uclk, 48000000);
> -		clk_prepare_enable(udc->uclk);
> +		clk_enable(udc->uclk);
>  	}
> -	clk_prepare_enable(udc->iclk);
> -	clk_prepare_enable(udc->fclk);
> +	clk_enable(udc->iclk);
> +	clk_enable(udc->fclk);
>  }
>  
>  static void clk_off(struct at91_udc *udc)
> @@ -884,10 +884,10 @@ static void clk_off(struct at91_udc *udc)
>  		return;
>  	udc->clocked = 0;
>  	udc->gadget.speed = USB_SPEED_UNKNOWN;
> -	clk_disable_unprepare(udc->fclk);
> -	clk_disable_unprepare(udc->iclk);
> +	clk_disable(udc->fclk);
> +	clk_disable(udc->iclk);
>  	if (IS_ENABLED(CONFIG_COMMON_CLK))
> -		clk_disable_unprepare(udc->uclk);
> +		clk_disable(udc->uclk);
>  }

As you stated prepare and unprepare should never be called in interrupt
context. 

My concern here is that PLLB (which is often used as USB clock
parent) will never be gated/disabled (because all this work is
done in its unprepare method), and thus your power consumption will be
higher (when entering suspend mode) than if you'd done a
disable_unprepare call.

How about leaving the clk_on/off unchanged and use a threaded irq
instead of a normal irq ?


Best Regards,

Boris

-- 
Boris Brezillon, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com