linux-kernel - [PATCH] atmel_spi: support zero length transfer

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Message-Id: <20080221.005432.07645461.anemo@mba.ocn.ne.jp>
Date:	Thu, 21 Feb 2008 00:54:32 +0900 (JST)
From:	Atsushi Nemoto <anemo@....ocn.ne.jp>
To:	Haavard Skinnemoen <hskinnemoen@...el.com>
Cc:	David Brownell <david-b@...bell.net>,
	spi-devel-general@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org
Subject: [PATCH] atmel_spi: support zero length transfer

A spi transfer with zero length is not invalid.  Such transfer can be
used to achieve delay before first CLK edge after chipselect assertion.

Signed-off-by: Atsushi Nemoto <anemo@....ocn.ne.jp>
---
diff --git a/drivers/spi/atmel_spi.c b/drivers/spi/atmel_spi.c
index 293b7ca..5dff5e0 100644
--- a/drivers/spi/atmel_spi.c
+++ b/drivers/spi/atmel_spi.c
@@ -606,7 +606,7 @@ static int atmel_spi_transfer(struct spi_device *spi, struct spi_message *msg)
 		return -ESHUTDOWN;
 
 	list_for_each_entry(xfer, &msg->transfers, transfer_list) {
-		if (!(xfer->tx_buf || xfer->rx_buf)) {
+		if (!(xfer->tx_buf || xfer->rx_buf) && xfer->len) {
 			dev_dbg(&spi->dev, "missing rx or tx buf\n");
 			return -EINVAL;
 		}
--
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