Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752076AbbEGPv6 (ORCPT ); Thu, 7 May 2015 11:51:58 -0400 Received: from mail-qc0-f174.google.com ([209.85.216.174]:33628 "EHLO mail-qc0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751342AbbEGPv4 (ORCPT ); Thu, 7 May 2015 11:51:56 -0400 Message-ID: <554B8A14.2080904@hurleysoftware.com> Date: Thu, 07 May 2015 11:51:48 -0400 From: Peter Hurley User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.6.0 MIME-Version: 1.0 To: "Dr. H. Nikolaus Schaller" CC: Mark Rutland , Pavel Machek , List for communicating with real GTA04 owners , NeilBrown , One Thousand Gnomes , Arnd Bergmann , Greg Kroah-Hartman , Sebastian Reichel , "grant.likely@linaro.org" , Jiri Slaby , "devicetree@vger.kernel.org" , "linux-kernel@vger.kernel.org" Subject: Re: [Gta04-owner] [PATCH 0/3] tty slave device support - version 3. References: <55492001.30806@hurleysoftware.com> <20150506092738.GB4508@amd> <554A03A7.2000504@hurleysoftware.com> <20150506123632.GA1764@leverpostej> <20150506141547.GB1764@leverpostej> <20150506171802.GE2974@leverpostej> <554B7D33.602@hurleysoftware.com> <9EF54D80-F634-4D59-BFD9-FC79FCFE06DE@goldelico.com> In-Reply-To: <9EF54D80-F634-4D59-BFD9-FC79FCFE06DE@goldelico.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2112 Lines: 47 On 05/07/2015 11:34 AM, Dr. H. Nikolaus Schaller wrote: > Am 07.05.2015 um 16:56 schrieb Peter Hurley : >> On 05/07/2015 08:46 AM, Dr. H. Nikolaus Schaller wrote: >> Both devicetree and tty/serial can already represent independent control; >> what is proposed is a way to express dependent control, and in all cases, >> that control stems directly from either the UART state itself or via >> commands sent over that interface. > > Yes. This is why I propose that the tty/uart driver can send an internal notification > to the device driver. And the device driver can register to be notified by the UART > that is identified by the phandle of the slave DT entry. I've not seen any code with your proposal, so that makes it impossible to compare competing solutions. >> Any target not requiring UART involvement doesn't (and probably, shouldn't) >> be expressed as a slave device. > > IMHO it is not obligatory to represent the direction of control by a parent>child > relation in DT. DT just needs to describe that there is a relation/connection. Devicetree usage in the linux kernel is for representing the host view, not an abstract machine. I have yet to see an example of a proposed tty slave where the host interface is not a UART. > The driver code already must “know” the direction of notifications. > > BTW, there can even be control in reverse direction in some cases. E.g. the slave > driver wants to automatically set the baud rate of the uart, i.e. the slave controls > the uart on /dev/tty side. > > If I have monitored some other discussion right, this is exactly done by a Codec > driver to tell its mcbsp counterpart about clock rates and data formats it should > expect. Maybe this is the reason why McBSP use (or are just happy with) the > phandle approach. Parameters are not control. Regards, Peter Hurley -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/