linux-kernel - Re: [PATCH 3/3] usb: misc: usb3503: Remove 100ms sleep on reset, conform to data sheet

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Date:	Sat, 1 Jun 2013 12:08:48 +0900
From:	Dongjin Kim <tobetter@...il.com>
To:	Julius Werner <jwerner@...omium.org>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Fengguang Wu <fengguang.wu@...el.com>,
	Wei Yongjun <yongjun_wei@...ndmicro.com.cn>,
	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
	Simon Glass <sjg@...omium.org>,
	Doug Anderson <dianders@...omium.org>,
	Olof Johansson <olofj@...omium.org>,
	Vivek Gautam <gautam.vivek@...sung.com>
Subject: Re: [PATCH 3/3] usb: misc: usb3503: Remove 100ms sleep on reset,
 conform to data sheet

Signed-off-by: Dongjin Kim <tobetter@...il.com>

On Sat, Jun 1, 2013 at 10:34 AM, Julius Werner <jwerner@...omium.org> wrote:
> The usb3503 driver sleeps a flat 100ms when resetting the chip, with a
> comment about waiting for the reference clock. This seems to be a
> board-specific detail that should not hold up boot across all platforms.
> This patch reduces the sleep to the 4ms initialization delay that the
> chip itself actually requires (as per its data sheet). If certain boards
> require more time to set up the reference clock, they should change this
> through local patches or add a proper, configurable synchronization
> mechanism.
>
> Signed-off-by: Julius Werner <jwerner@...omium.org>
> ---
>  drivers/usb/misc/usb3503.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/usb/misc/usb3503.c b/drivers/usb/misc/usb3503.c
> index a647a2e..a1d509f 100644
> --- a/drivers/usb/misc/usb3503.c
> +++ b/drivers/usb/misc/usb3503.c
> @@ -107,11 +107,9 @@ static int usb3503_reset(int gpio_reset, int state)
>         if (gpio_is_valid(gpio_reset))
>                 gpio_set_value(gpio_reset, state);
>
> -       /* Wait RefClk when RESET_N is released, otherwise Hub will
> -        * not transition to Hub Communication Stage.
> -        */
> +       /* Wait T_HUBINIT == 4ms for hub logic to stabilize */
>         if (state)
> -               msleep(100);
> +               usleep_range(4000, 10000);
>
>         return 0;
>  }
> --
> 1.7.12.4
>
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