linux-kernel - Re: [RFC] tty (or char) bus?

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Date:	Fri, 17 Jul 2009 13:54:28 -0400
From:	Samuel Thibault <samuel.thibault@...-lyon.org>
To:	Janusz Krzysztofik <jkrzyszt@....icnet.pl>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
	"alsa-devel@...a-project.org" <alsa-devel@...a-project.org>
Subject: Re: [RFC] tty (or char) bus?

Hello,

Janusz Krzysztofik, le Tue 14 Jul 2009 17:31:23 +0200, a écrit :
> In my attempt to add support for contols to a voice modem codec sound 
> device driver, I found that in order to talk to the modem, it would be 
> convenient if I can get access to a tty device from inside the kernel in 
> a way similiar to that available form userspace.

I agree.

> AFAICS, even if tty lowlevel write() could be used unmodified, a
> convenient way of reading characters from a tty is missing and should
> be implemented in a line discipline. Please correct me if I am wrong.

Have you seen the receive_buf line discipline hook?  Indeed it's not a
read() operation as from userland, but at least you can get the data
from the tty that way.

> OTOH, I found that some kind of abstraction layer for acccessing devices 
> over a tty could be convenient. Instead of allocating a new line 
> discipline for each specific device, sometimes found on a specific board 
> only, why not just create a new bus type?

I'd tend to agree with you, as I also have a use case for that: braille
& speech synthesis devices.  However for now I haven't found a really
convincing argument why line disciplines aren't enough.

Samuel
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