linux-kernel - spi transfer with zero length

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Message-Id: <20080216.230232.25478328.anemo@mba.ocn.ne.jp>
Date:	Sat, 16 Feb 2008 23:02:32 +0900 (JST)
From:	Atsushi Nemoto <anemo@....ocn.ne.jp>
To:	David Brownell <david-b@...bell.net>,
	spi-devel-general@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org
Subject: spi transfer with zero length

Hi.  Is it legal to use zero for 'len' field of struct spi_transfer?
I mean, len=0, tx_buf=rx_buf=NULL, delay_usecs!=0.

Some SPI devices need slightly long delay before first CLK edge after
CS assertion.  To achieve this, I think inserting using a zero length
transfer before real transfers.  But it seems some drivers do not
handle this case properly.

Is this driver's bug, or we need additional delay field in struct
spi_device for such case?

---
Atsushi Nemoto
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