linux-kernel - Re: [PATCH RFC 0/5] *** SPI Slave mode support ***

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Message-ID: <20170425080738.cb6jaqvktgpir7zq@pengutronix.de>
Date:   Tue, 25 Apr 2017 10:07:38 +0200
From:   Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
To:     Jiada Wang <jiada_wang@...tor.com>
Cc:     Geert Uytterhoeven <geert@...ux-m68k.org>,
        Mark Rutland <mark.rutland@....com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Rob Herring <robh+dt@...nel.org>,
        linux-spi <linux-spi@...r.kernel.org>,
        Mark Brown <broonie@...nel.org>,
        Sascha Hauer <kernel@...gutronix.de>,
        Fabio Estevam <fabio.estevam@....com>,
        Shawn Guo <shawnguo@...nel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH RFC 0/5] *** SPI Slave mode support ***

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/  |