linux-kernel - [PATCH 3.16 036/254] mfd: cros ec: spi: Don't send first message too soon

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Message-ID: <lsq.1519831218.672675594@decadent.org.uk>
Date:   Wed, 28 Feb 2018 15:20:18 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org,
        "Douglas Anderson" <dianders@...omium.org>,
        "Jon Hunter" <jonathanh@...dia.com>,
        "Lee Jones" <lee.jones@...aro.org>,
        "Brian Norris" <briannorris@...omium.org>,
        "Benson Leung" <bleung@...omium.org>
Subject: [PATCH 3.16 036/254] mfd: cros ec: spi: Don't send first message
 too soon

3.16.55-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Jon Hunter <jonathanh@...dia.com>

commit 15d8374874ded0bec37ef27f8301a6d54032c0e5 upstream.

On the Tegra124 Nyan-Big chromebook the very first SPI message sent to
the EC is failing.

The Tegra SPI driver configures the SPI chip-selects to be active-high
by default (and always has for many years). The EC SPI requires an
active-low chip-select and so the Tegra chip-select is reconfigured to
be active-low when the EC SPI driver calls spi_setup(). The problem is
that if the first SPI message to the EC is sent too soon after
reconfiguring the SPI chip-select, it fails.

The EC SPI driver prevents back-to-back SPI messages being sent too
soon by keeping track of the time the last transfer was sent via the
variable 'last_transfer_ns'. To prevent the very first transfer being
sent too soon, initialise the 'last_transfer_ns' variable after calling
spi_setup() and before sending the first SPI message.

Signed-off-by: Jon Hunter <jonathanh@...dia.com>
Reviewed-by: Brian Norris <briannorris@...omium.org>
Reviewed-by: Douglas Anderson <dianders@...omium.org>
Acked-by: Benson Leung <bleung@...omium.org>
Signed-off-by: Lee Jones <lee.jones@...aro.org>
[bwh: Backported to 3.16: use ktime_get_ts() and timespec_to_ns()]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
--- a/drivers/mfd/cros_ec_spi.c
+++ b/drivers/mfd/cros_ec_spi.c
@@ -347,6 +347,7 @@ static int cros_ec_spi_probe(struct spi_
 	struct device *dev = &spi->dev;
 	struct cros_ec_device *ec_dev;
 	struct cros_ec_spi *ec_spi;
+	struct timespec ts;
 	int err;

 	spi->bits_per_word = 8;
@@ -379,6 +380,9 @@ static int cros_ec_spi_probe(struct spi_
 	ec_dev->din_size = EC_MSG_BYTES + EC_MSG_PREAMBLE_COUNT;
 	ec_dev->dout_size = EC_MSG_BYTES;

+	ktime_get_ts(&ts);
+	ec_spi->last_transfer_ns = timespec_to_ns(&ts);
+
 	err = cros_ec_register(ec_dev);
 	if (err) {
 		dev_err(dev, "cannot register EC\n");