linux-kernel - Re: [PATCH 4/6] drivers:misc: sources for Init manager module

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Date:	Wed, 24 Mar 2010 21:52:56 +0530 (IST)
From:	Pavan Savoy <pavan_savoy@...oo.co.in>
To:	Marcel Holtmann <marcel@...tmann.org>
Cc:	Greg KH <gregkh@...e.de>, PavanSavoy <pavan_savoy@...com>,
	"alan@...rguk.ukuu.org.uk" <alan@...rguk.ukuu.org.uk>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/6] drivers:misc: sources for Init manager module

--- On Wed, 24/3/10, Marcel Holtmann <marcel@...tmann.org> wrote:

> From: Marcel Holtmann <marcel@...tmann.org>
> Subject: Re: [PATCH 4/6] drivers:misc: sources for Init manager module
> To: "Pavan Savoy" <pavan_savoy@...oo.co.in>
> Cc: "Greg KH" <gregkh@...e.de>, "PavanSavoy" <pavan_savoy@...com>, "alan@...rguk.ukuu.org.uk" <alan@...rguk.ukuu.org.uk>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
> Date: Wednesday, 24 March, 2010, 9:41 PM
> Hi Pavan,
> 
> 
> > I wanted to somehow put this in staging because then
> it would probably have a thorough architectural review
> process.
> > Some details about this driver - 
> > 
> > 1. This driver will be used by Bluetooth-BlueZ/FM-V4L2
> and GPS (probably character device driver) using the
> EXPORTED symbols (-register/_unregister).
> > 
> > 2. Much like the hciattach daemon which maintains
> N_HCI bluetooth line discipline, this driver will also have
> a User-Space  N_TI_WL Init manager (UIM) maintaining
> the Line discipline.
> 
> can you explain why you think this is needed and we can not
> interface
> this directly. If it is a serial port, what protocol does
> it talk?

Illustration: The BT driver on top of this ST driver, would create a hci0 interface, when someone does an DEVUP on that interface, the BT driver would then do a st-register - which in-turn would ask the hciattach-like daemon to install the line discipline for it via the sysfs entry.
The same concept goes for FM-V4L2 and GPS character driver.

The core of the problem is we cannot ask/install/ldisc_put for a line discipline from kernel space.

> 
> > 3. Because of the UIM should know when to
> install/uninstall line discipline, the /sys entry is created
> a root called UIM (a new kobject) and UIM daemon would write
> it's PID to it.
> 
> I don't understand this. This sounds like a broken concept
> to me.

Yes, I don't feel good about it either. But how do I request for a line discipline from kernel space ?
Currently a daemon has to run in user-space to maintain the ldisc, at all times, and I don't want to open TTY @ boot, and install Ldisc (tiocsetd) on it, without BT/FM or GPS core on chip being used - The Power Management team here would beat me up if I do that, 
and hence the very dumb idea of passing the PID of the daemon via sysfs entry, and the driver sending SIGUSR2 to that PID, daemon doing a tiocsetd upon that signal.

> 
> > 4. As Alan suggested, If I make it self-contained by
> pushing number of line disciplines to a slightly larger
> number, then would it be OK ?
> 
> Just from a quick look, I think within a few review cycles
> this might be
> able to get proper upstream inclusion. No idea why bother
> with staging
> in the first place. Lets do this correctly.
> 

The only reason I wanted this to be in staging was to have sort of continuous review process, and in hope the driver wouldn't be forgotten.

> Regards
> 
> Marcel
> 
> 
> 

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