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, 9 insertions, 0 deletions

diff --git a/Documentation/devicetree/bindings/mfd/cros-ec.txt b/Documentation/devicetree/bindings/mfd/cros-ec.txt
index 5f229c5..8009c3d 100644
--- a/Documentation/devicetree/bindings/mfd/cros-ec.txt
+++ b/Documentation/devicetree/bindings/mfd/cros-ec.txt
@@ -17,6 +17,15 @@ Required properties (SPI):
 - compatible: "google,cros-ec-spi"
 - reg: SPI chip select
 
+Optional properties (SPI):
+- google,cros-ec-spi-msg-delay: Some implementations of the EC require some
+  additional processing time in order to accept new transactions. If the delay
+  between transactions is not long enough the EC may not be able to respond
+  properly to subsequent transactions and cause them to hang. This property
+  specifies the delay, in usecs, introduced between transactions to account
+  for the time required by the EC to get back into a state in which new data
+  can be accepted.
+
 Required properties (LPC):
 - compatible: "google,cros-ec-lpc"
 - reg: List of (IO address, size) pairs defining the interface uses