linux-kernel - [PATCH 1/2] mfd: cros_ec: spi: Fix end of transfer on devices with no spi-msg-delay

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Date:	Fri, 13 Jun 2014 11:13:32 -0700
From:	Doug Anderson <dianders@...omium.org>
To:	Samuel Ortiz <sameo@...ux.intel.com>,
	Lee Jones <lee.jones@...aro.org>,
	Kukjin Kim <kgene.kim@...sung.com>
Cc:	Tomasz Figa <tomasz.figa@...il.com>, broonie@...nel.org,
	sjg@...omium.org, olof@...om.net, javier.martinez@...labora.co.uk,
	ch.naveen@...sung.com, swarren@...dotorg.org, khilman@...aro.org,
	ajaynumb@...il.com, rahul.sharma@...sung.com, tushar.b@...sung.com,
	linux-samsung-soc@...r.kernel.org,
	Doug Anderson <dianders@...omium.org>,
	linux-kernel@...r.kernel.org
Subject: [PATCH 1/2] mfd: cros_ec: spi: Fix end of transfer on devices with no spi-msg-delay

cros_ec_spi makes the assumption that a 0-length message will put the
spi chip select back to normal (non cs_toggle mode).  This used to be
the case back on kernel-3.8 on the spi-s3c64xx driver but doesn't
appear to be true anymore.  It seems like it was a pretty questionable
assumption to begin with, so let's fix the code to be more robust.  We
know that a message with a single 0-length segment _will_ put things
back in order.  Change cros_ec_spi to handle this.

This wasn't a problem on the main user of cros_ec_spi upstream (tegra)
because it specified 'google,cros-ec-spi-msg-delay'.

Signed-off-by: Doug Anderson <dianders@...omium.org>
---
 drivers/mfd/cros_ec_spi.c | 18 +++++++-----------
 1 file changed, 7 insertions(+), 11 deletions(-)

diff --git a/drivers/mfd/cros_ec_spi.c b/drivers/mfd/cros_ec_spi.c
index 0b8d328..0cbc3db 100644
--- a/drivers/mfd/cros_ec_spi.c
+++ b/drivers/mfd/cros_ec_spi.c
@@ -266,18 +266,14 @@ static int cros_ec_command_spi_xfer(struct cros_ec_device *ec_dev,
 		dev_err(ec_dev->dev, "spi transfer failed: %d\n", ret);
 	}
 
-	/* turn off CS */
+	/*
+	 * Turn off CS, possibly adding a delay to ensure the rising edge
+	 * doesn't come too soon after the end of the data.
+	 */
 	spi_message_init(&msg);
-
-	if (ec_spi->end_of_msg_delay) {
-		/*
-		 * Add delay for last transaction, to ensure the rising edge
-		 * doesn't come too soon after the end of the data.
-		 */
-		memset(&trans, 0, sizeof(trans));
-		trans.delay_usecs = ec_spi->end_of_msg_delay;
-		spi_message_add_tail(&trans, &msg);
-	}
+	memset(&trans, 0, sizeof(trans));
+	trans.delay_usecs = ec_spi->end_of_msg_delay;
+	spi_message_add_tail(&trans, &msg);
 
 	final_ret = spi_sync(ec_spi->spi, &msg);
 	ktime_get_ts(&ts);
-- 
2.0.0.526.g5318336

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