linux-kernel - Re: [PATCH v4] Staging: comedi: convert while loop to timeout in ni_mio

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Date:	Wed, 15 Jan 2014 18:30:40 -0800
From:	Greg KH <gregkh@...uxfoundation.org>
To:	Hartley Sweeten <HartleyS@...ionengravers.com>
Cc:	Chase Southwood <chase.southwood@...oo.com>,
	"devel@...verdev.osuosl.org" <devel@...verdev.osuosl.org>,
	"abbotti@....co.uk" <abbotti@....co.uk>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4] Staging: comedi: convert while loop to timeout in
 ni_mio_common.c

On Wed, Jan 15, 2014 at 06:29:21PM +0000, Hartley Sweeten wrote:
> On Tuesday, January 14, 2014 8:59 PM, Greg KH wrote:
> > Sleep for at least 10, as I think that's the smallest time delay you can
> > sleep for anyway (meaning it will be that long no matter what number you
> > put there less than 10, depending on the hardware used of course.)
> 
> A bit off topic here but I have a somewhat related question about timeouts.
> 
> There are a number of comedi drivers that do a "wait for end-of-conversion"
> as part of the (*insn_read) for an analog input subdevice or (*insn_write) for
> an analog output subdevice. These functions return an errno if a timeout occurs.
> 
> Currently either -ETIME or -ETIMEDOUT is returned. This errno ends up getting
> returned to the user as the result of the unlocked_ioctl file operation. What is
> the more appropriate errno? Or is there is better one that should be used?

I think they should all be -ETIMEDOUT, -ETIME is used for something
else, and shouldn't be sent to userspace as I don't think it knows what
to do with it.

thanks,

greg k-h
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