Patch "mfd: cros ec: spi: Don't send first message too soon" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

mfd: cros ec: spi: Don't send first message too soon

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
mfd-cros-ec-spi-don-t-send-first-message-too-soon.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Jon Hunter <[email protected]>
Date: Tue, 14 Nov 2017 14:43:27 +0000
Subject: mfd: cros ec: spi: Don't send first message too soon

From: Jon Hunter <[email protected]>

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.

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

@@ -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) {

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/mfd-cros-ec-spi-don-t-send-first-message-too-soon.patch