linux-kernel - [PATCH 4.9 04/21] mfd: cros ec: spi: Dont send first message too soon

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Date:   Wed, 27 Dec 2017 17:46:20 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Jon Hunter <jonathanh@...dia.com>,
        Brian Norris <briannorris@...omium.org>,
        Douglas Anderson <dianders@...omium.org>,
        Benson Leung <bleung@...omium.org>,
        Lee Jones <lee.jones@...aro.org>
Subject: [PATCH 4.9 04/21] mfd: cros ec: spi: Dont send first message too soon

4.9-stable 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>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/mfd/cros_ec_spi.c |    1 +
 1 file changed, 1 insertion(+)

--- a/drivers/mfd/cros_ec_spi.c
+++ b/drivers/mfd/cros_ec_spi.c
@@ -664,6 +664,7 @@ static int cros_ec_spi_probe(struct spi_
 			   sizeof(struct ec_response_get_protocol_info);
 	ec_dev->dout_size = sizeof(struct ec_host_request);

+	ec_spi->last_transfer_ns = ktime_get_ns();

 	err = cros_ec_register(ec_dev);
 	if (err) {