linux-kernel - Re: [PATCH 1/1] usb: usleep_range is preferred over udelay where wakeup is flexible

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Date:	Wed, 24 Jun 2015 09:44:31 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Sunny Kumar <sunny.kumar.roy@...il.com>
cc:	mdharm-usb@...-eyed-alien.net, <gregkh@...uxfoundation.org>,
	<linux-usb@...r.kernel.org>,
	<usb-storage@...ts.one-eyed-alien.net>,
	<linux-kernel@...r.kernel.org>, <swt.sunny@...il.com>
Subject: Re: [PATCH 1/1] usb: usleep_range is preferred over udelay where
 wakeup is flexible

On Wed, 24 Jun 2015, Sunny Kumar wrote:

> According to Documentation/timers/timers-howto.txt"
> udelay() is only called once from a place where sleeping is allowed.
> We can replace it with a call to usleep_range()
> with a reasonable upper limit.
> 
> Signed-off-by: Sunny Kumar <sunny.kumar.roy@...il.com>
> ---
>  drivers/usb/storage/transport.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/usb/storage/transport.c b/drivers/usb/storage/transport.c
> index 540add2..7cd45ac 100644
> --- a/drivers/usb/storage/transport.c
> +++ b/drivers/usb/storage/transport.c
> @@ -1111,7 +1111,7 @@ int usb_stor_Bulk_transport(struct scsi_cmnd *srb, struct us_data *us)
>  	 * command phase and the data phase.  Some devices need a little
>  	 * more than that, probably because of clock rate inaccuracies. */
>  	if (unlikely(us->fflags & US_FL_GO_SLOW))
> -		udelay(125);
> +		usleep_range(100, 125);

You said you were going to use a reasonable upper limit.  Instead, you 
left the upper limit the same and decreased the lower limit, which 
could cause errors.

Alan Stern

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