Re: [PATCH 1/1] mct_u232: added _ioctl, _msr_to_icount and _get_icount functions

[Tsozik <tsozik@yahoo.com>]

Greg,

I'm sorry to bother you again, but I'm wondering if you could comment on Pete's concern below.

Thank you in advance for your expertise on the matter,
 Vadim. 

--- On Tue, 12/28/10, Pete Zaitcev <zaitcev@redhat.com> wrote:

> From: Pete Zaitcev <zaitcev@redhat.com>
> Subject: Re: [PATCH 1/1] mct_u232: added _ioctl, _msr_to_icount and _get_icount functions
> To: "Tsozik" <tsozik@yahoo.com>
> Cc: "Greg Kroah-Hartman" <gregkh@suse.de>, linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org, zaitcev@redhat.com
> Date: Tuesday, December 28, 2010, 1:40 AM
> On Mon, 27 Dec 2010 20:04:51 -0800
> (PST)
> Tsozik <tsozik@yahoo.com>
> wrote:
> 
> > So I ran geiger counter against /dev/ttyS0 device for
> 20 minutes and
> > acquired 20 measurements. Then I compared last average
> with last 20
> > minute measurement average acquired via mct_u232 on
> the laptop placed
> > nearby. The error was ~4% (rounded up).
> 
> Great, I'm ready to ack.
> 
> There's just one thing that is bugging me... I think it
> would be best
> if Alan Cox or Greg Kroah commented on it. The edgeport
> does the
> following, which we copied:
> 
> 
>         schedule();
>         ........
>         if (cnow.rng ==
> cprev.rng && cnow.dsr == cprev.dsr &&
>            
> cnow.dcd == cprev.dcd && cnow.cts == cprev.cts)
>            
> return -EIO; /* no change => error */
>         if (((arg &
> TIOCM_RNG) && (cnow.rng != cprev.rng)) ||
>             ((arg
> & TIOCM_DSR) && (cnow.dsr != cprev.dsr)) ||
>             ((arg
> & TIOCM_CD)  && (cnow.dcd != cprev.dcd))
> ||
>             ((arg
> & TIOCM_CTS) && (cnow.cts != cprev.cts))) {
>            
> return 0;
>         }
> 
> So, if there was a status report, but no change to bits,
> the ioctl
> TIOCMIWAIT would return with -EIO. In serial_core.c, that
> serves
> conventional non-USB UARTs, nothing like this occurs. I am
> not quite
> sure what the point of doing this -EIO check is.
> 
> Oh and BTW, I'm wondering what is going to happen if the
> device is
> disconnected while an application is blocked waiting for
> the status
> change. The patch is not particularly bad here, it just
> copies
> an existing code from elsewhere.
> 
> -- Pete
>