From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1176492AbdDYILl (ORCPT <rfc822;w@1wt.eu>);
        Tue, 25 Apr 2017 04:11:41 -0400
Received: from metis.ext.4.pengutronix.de ([92.198.50.35]:33901 "EHLO
        metis.ext.4.pengutronix.de" rhost-flags-OK-OK-OK-OK)
        by vger.kernel.org with ESMTP id S1171531AbdDYIHn (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Tue, 25 Apr 2017 04:07:43 -0400
Date: Tue, 25 Apr 2017 10:07:38 +0200
From: Uwe =?iso-8859-1?Q?Kleine-K=F6nig?= 
        <u.kleine-koenig@pengutronix.de>
To: Jiada Wang <jiada_wang@mentor.com>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>,
        Mark Rutland <mark.rutland@arm.com>,
        "devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Rob Herring <robh+dt@kernel.org>,
        linux-spi <linux-spi@vger.kernel.org>, Mark Brown <broonie@kernel.org>,
        Sascha Hauer <kernel@pengutronix.de>,
        Fabio Estevam <fabio.estevam@nxp.com>, Shawn Guo <shawnguo@kernel.org>,
        "linux-arm-kernel@lists.infradead.org" 
        <linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH RFC 0/5] *** SPI Slave mode support ***
Message-ID: <20170425080738.cb6jaqvktgpir7zq@pengutronix.de>
References: <1492085644-4195-1-git-send-email-jiada_wang@mentor.com>
 <20170413125929.dygodgj6c35ydh5p@sirena.org.uk>
 <CAMuHMdUm=90ddNWM5KWqT+W0hqZ-QO6vPHj5OisbYquDYq1ZmA@mail.gmail.com>
 <58F06092.9080409@mentor.com>
 <CAMuHMdXa_O6RsqUciiNWQ0Zp6dniS47AUmPN9UWAWitP0csx=Q@mail.gmail.com>
 <58FDF430.5090306@mentor.com>
 <CAMuHMdVQS494-BAc-W-XOOLK8Xow85n+Cgih0FG+t4QxCFxhMA@mail.gmail.com>
 <58FF0127.7070703@mentor.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=iso-8859-1
Content-Disposition: inline
Content-Transfer-Encoding: 8bit
In-Reply-To: <58FF0127.7070703@mentor.com>
User-Agent: Mutt/1.6.2-neo (2016-06-11)
X-SA-Exim-Connect-IP: 2001:67c:670:100:1d::c5
X-SA-Exim-Mail-From: ukl@pengutronix.de
X-SA-Exim-Scanned: No (on metis.ext.pengutronix.de); SAEximRunCond expanded to false
X-PTX-Original-Recipient: linux-kernel@vger.kernel.org
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

Hello Jiada,

On Tue, Apr 25, 2017 at 12:56:23AM -0700, Jiada Wang wrote:
> the use case of
> "A (master) <=> B (slave)", "B (master) <=> C(slave)", do share MISO and
> MOSI lines,
> but there is no SS line between A and C. so for each SPI slave device, there
> is only one
> master device.

So you need a mutex to make A not use the bus while B communicates to C.
Otherwise you have two drivers on MOSI (A and B) and MISO (B and C).

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |