linux-kernel - RE: [PATCH 1/2] drivers:staging:ti-st: move TI

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Date:	Thu, 7 Oct 2010 20:22:32 +0530
From:	"Savoy, Pavan" <pavan_savoy@...com>
To:	Jiri Slaby <jirislaby@...il.com>
CC:	"gregkh@...e.de" <gregkh@...e.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devel@...verdev.osuosl.org" <devel@...verdev.osuosl.org>,
	"alan@...rguk.ukuu.org.uk" <alan@...rguk.ukuu.org.uk>
Subject: RE: [PATCH 1/2] drivers:staging:ti-st: move TI_ST from staging




> -----Original Message-----
> From: Jiri Slaby [mailto:jirislaby@...il.com]
> Sent: Thursday, October 07, 2010 2:59 AM
> To: Savoy, Pavan
> Cc: gregkh@...e.de; linux-kernel@...r.kernel.org; devel@...verdev.osuosl.org;
> alan@...rguk.ukuu.org.uk
> Subject: Re: [PATCH 1/2] drivers:staging:ti-st: move TI_ST from staging
> 
> On 10/07/2010 12:36 AM, Savoy, Pavan wrote:
> >>>>> +int st_core_init(struct st_data_s **core_data)
> >>>>> +{
> >>>>> +	struct st_data_s *st_gdata;
> >>>>> +	long err;
> >>>>> +	static struct tty_ldisc_ops *st_ldisc_ops;
> >>>>> +
> >>>>> +	/* populate and register to TTY line discipline */
> >>>>> +	st_ldisc_ops = kzalloc(sizeof(*st_ldisc_ops), GFP_KERNEL);
> >>>>> +	if (!st_ldisc_ops) {
> >>>>> +		pr_err("no mem to allocate");
> >>>>> +		return -ENOMEM;
> >>>>> +	}
> >>>> This can be static structure, you don't need to allocate this on heap.
> >>>> It should be a singleton.
> >>>
> >>> Yes, I got this comment before, but is it just a style issue?
> >>> I want to keep this in heap because some day, I hope TTY ldics have their
> >> own
> >>> private_data, which I can pass around like the tty_struct's data.
> >>> and having them in heap, I plan to keep a reference to ops structure, so
> >> that I
> >>> can pass around and use ops->private_data everywhere ..
> >>
> >> I doubt ldisc ops will ever have ->private_data. What would you need it
> >> for? The ops generally work with ttys which have ->disc_data.
> >
> > Yes, But in this case, I required something which can be set during
> ldisc_register, and can be picked up during tty_open.
> 
> Why? ldiscs are per-system, singletons, not per-device. So you should
> not bind to them any device specific info.


Per-system? I don't understand this.
There can be ldisc for each individual TTY, so doesn't that make it per device?
Or to be even more specific, it makes it per-TTY which is mapped to a particular device, UART/a-set of usb-endpoints etc...

This driver in fact does just that, it is a driver which allows sharing of the TTY by many other drivers (I call it the protocol drivers).

> --
> js
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