linux-kernel - Re: [PATCH 4/5] spi: Check that Quad/Dual is half duplex

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Message-ID: <20140121182130.GM17314@sirena.org.uk>
Date:	Tue, 21 Jan 2014 18:21:30 +0000
From:	Mark Brown <broonie@...nel.org>
To:	Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:	linux-spi@...r.kernel.org, linux-kernel@...r.kernel.org,
	Geert Uytterhoeven <geert+renesas@...ux-m68k.org>
Subject: Re: [PATCH 4/5] spi: Check that Quad/Dual is half duplex

On Tue, Jan 21, 2014 at 04:10:08PM +0100, Geert Uytterhoeven wrote:
> From: Geert Uytterhoeven <geert+renesas@...ux-m68k.org>
> 
> Quad and Dual SPI Transfers use all available data lines (incl. MOSI/MISO),
> hence they must be half duplex. Add a check that verify that.

This is surprising to me - I had expected that there would be extra
signals that would be used for these modes, not that the opposite
direction data line would be one of the ones being reused.  On the other
hand if this is what all the flash chips do then it would seem
reasonable that controllers do the same.  Can you clarify please?

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