Messages in this thread | | | Date | Thu, 25 Mar 2010 02:33:42 +0530 (IST) | From | Pavan Savoy <> | Subject | Re: [PATCH 4/6] drivers:misc: sources for Init manager module |
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Marcel,
--- On Thu, 25/3/10, Marcel Holtmann <marcel@holtmann.org> wrote:
> From: Marcel Holtmann <marcel@holtmann.org> > Subject: Re: [PATCH 4/6] drivers:misc: sources for Init manager module > To: "Pavan Savoy" <pavan_savoy@yahoo.co.in> > Cc: "Alan Cox" <alan@lxorguk.ukuu.org.uk>, "Greg KH" <gregkh@suse.de>, "PavanSavoy" <pavan_savoy@ti.com>, "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org> > Date: Thursday, 25 March, 2010, 2:24 AM > Hi Pavan, > > > > > Which puts me back to square 1, > > > the requirement is TTY device should be open, > only when > > > either BT, FM or GPS would want to use it. > > > > [with your patch one of the steps of > installing ldisc > > > would be reduced upon opening]. > > > > > > Perhaps but its up to you how you write your low > level > > > driver and how the > > > ldisc indicates it wishes to be active (eg speed > B0 is used > > > to indicate > > > 'no carrier' in many cases) > > > > > > > Actually why do I even need a TTY device in > this case > > > - right ? > > > > ldisc driver can do the > tty->ops->write and > > > tty_read and put it up on different interfaces > like > > > eth0/hci0 or /dev/radio0 etc.. > > > > > > You don't need a tty if you are simply demuxing > some kind > > > of stream of > > > bytes to/from the hardware and you gain nothing > from the > > > tty layer and > > > user space interfaces such as control signal and > speed > > > setting. > > > > > > > I still want to maintain this as a ldisc driver and > the TTY layer is still required to be able to use this with > different sort of serial drivers. > > > > example: > > We do a have a system here where both 8250/omap-serial > co-exist creating their own device nodes (ttyS for 8250, > ttyO for omap-serial) and I would want to be able to on boot > suggest which serial driver to use, so I can open/install > ldisc on ttyS or on ttyO. > > > > > > > That may be even cleaner in your case as you can > then then > > > provide > > > suitable links between your demux and the drivers > attached > > > to it > > > indicating when they should be on or off. > > > > And as Marcel suggested, can't really put in the > PM/UART-clk shut off code in ldisc driver because few of > these driver provide interfaces and few don't. > > > > So is there no way this can be accepted with the sysfs > entry way of communication ? > > to be quite honest, I can't see how that can be accepted > right now. It > looks wrong on too many levels.
Sigh - So to save power, and open/install tty-ldisc only when required, the sysfs entry was introduced. So now I guess I have 2 options :-
1. Fix the UART/LDISC upon boot by the daemon, get away with the sysfs entry + signaling altogether. 2. find a better way of telling the user-space daemon to open/install the line discipline.
- So any suggestions on option 2 ? like some event mechanism which is simple and clean ?
While we are at it, I will send across the BT driver too which makes use of this LDISC.
> > Regards > > Marcel > > >
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