linux-kernel - Re: [PATCH 1/2] tty/hvc_console: Add DTR/RTS callback to handle HUPCL control

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Date:	Wed, 16 Oct 2013 18:21:12 -0500
From:	Benjamin Herrenschmidt <benh@....ibm.com>
To:	Hendrik Brueckner <brueckner@...ux.vnet.ibm.com>
Cc:	jslaby@...e.cz, gregkh@...uxfoundation.org,
	brueckner@...ux.vnet.com, heiko.carstens@...ibm.com,
	schwidefsky@...ibm.com, linuxppc-dev@...ts.ozlabs.org,
	linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org
Subject: Re: [PATCH 1/2] tty/hvc_console: Add DTR/RTS callback to handle
 HUPCL control

On Wed, 2013-10-16 at 11:04 +0200, Hendrik Brueckner wrote:
> Indeed, two callbacks change the DTR line.  The main difference is that
> tiocmget/tiocmset can be called from user space by ioctl.  That's not the case
> for the dtr_cts callback.  Also, tiocmget/tiocmset provide more flags that can
> be changed (ST, SR, CTS, CD, RNG, RI,  ...)
> 
> Assume we would like to unify them have a single callback to change DTR, then
> we have to take care of these differences.  So the question to you now is
> whether you plan for a) other modem flags to be changed and b) if changing the
> DTR line (or other control flags) through an ioctl?
> 
> Depending on your results, I could work on sth that helps us both and reduces
> the callbacks.

Can we not just have the users of dtr_cts just call the backend's tiocmset ?

If they need to filter or clamp bits, we could handle all that in hvc_console
by caching the user intended value and passing a cooked value down to the backend..

None of that is urgent or anything, it's just odd and would be nice to cleanup.

Cheers,
Ben.


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