mfd: cros ec: spi: Add delay for raising CS

The EC has specific timing it requires. Add support for an optional delay
after raising CS to fix timing issues. This is configurable based on
a DT property "google,cros-ec-spi-msg-delay".

If this property isn't set, then no delay will be added. However, if set
it will cause a delay equal to the value passed to it to be inserted at
the end of a transaction.

Signed-off-by: Rhyland Klein <rklein@nvidia.com>
Reviewed-by: Bernie Thompson <bhthompson@chromium.org>
Reviewed-by: Andrew Bresticker <abrestic@chromium.org>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

1 files changed, 29 insertions, 0 deletions

diff --git a/drivers/mfd/cros_ec_spi.c b/drivers/mfd/cros_ec_spi.c
index 005403643539..84af8d7a4295 100644
--- a/drivers/mfd/cros_ec_spi.c
+++ b/drivers/mfd/cros_ec_spi.c
@@ -18,6 +18,7 @@
 #include <linux/module.h>
 #include <linux/mfd/cros_ec.h>
 #include <linux/mfd/cros_ec_commands.h>
+#include <linux/of.h>
 #include <linux/platform_device.h>
 #include <linux/slab.h>
 #include <linux/spi/spi.h>
@@ -62,10 +63,13 @@
  * @spi: SPI device we are connected to
  * @last_transfer_ns: time that we last finished a transfer, or 0 if there
  *      if no record
+ * @end_of_msg_delay: used to set the delay_usecs on the spi_transfer that
+ *      is sent when we want to turn off CS at the end of a transaction.
  */
 struct cros_ec_spi {
         struct spi_device *spi;
         s64 last_transfer_ns;
+        unsigned int end_of_msg_delay;
 };
 
 static void debug_packet(struct device *dev, const char *name, u8 *ptr,
@@ -238,6 +242,17 @@ static int cros_ec_command_spi_xfer(struct cros_ec_device *ec_dev,
 
         /* turn off CS */
         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);
+        }
+
         final_ret = spi_sync(ec_spi->spi, &msg);
         ktime_get_ts(&ts);
         ec_spi->last_transfer_ns = timespec_to_ns(&ts);
@@ -284,6 +299,17 @@ static int cros_ec_command_spi_xfer(struct cros_ec_device *ec_dev,
         return 0;
 }
 
+static void cros_ec_spi_dt_probe(struct cros_ec_spi *ec_spi, struct device *dev)
+{
+        struct device_node *np = dev->of_node;
+        u32 val;
+        int ret;
+
+        ret = of_property_read_u32(np, "google,cros-ec-spi-msg-delay", &val);
+        if (!ret)
+                ec_spi->end_of_msg_delay = val;
+}
+
 static int cros_ec_spi_probe(struct spi_device *spi)
 {
         struct device *dev = &spi->dev;
@@ -305,6 +331,9 @@ static int cros_ec_spi_probe(struct spi_device *spi)
         if (!ec_dev)
                 return -ENOMEM;
 
+        /* Check for any DT properties */
+        cros_ec_spi_dt_probe(ec_spi, dev);
+
         spi_set_drvdata(spi, ec_dev);
         ec_dev->name = "SPI";
         ec_dev->dev = dev;