[PATCH v5 1/2] mfd: cros ec: spi: Add delay for raising CS

Thierry Reding
2013-12-16T11:11:11Z

From: Rhyland Klein <rklein@nvidia.com>

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>
---
Changes in v5:
- modify correct hunk to use 0 instead of '\0'
- add Mark's Acked-by

Changes in v4:
- unconditionally call cros_ec_spi_dt_probe() since the driver now
depends on OF

Changes in v3:
- rename cros_ec_probe_spi_dt() to cros_ec_spi_dt_probe()
- use 0 instead of '\0'

Changes in v2:
- make property description more verbose

Documentation/devicetree/bindings/mfd/cros-ec.txt | 9 +++++++
drivers/mfd/cros_ec_spi.c | 29 +++++++++++++++++++++++
2 files changed, 38 insertions(+)

diff --git a/Documentation/devicetree/bindings/mfd/cros-ec.txt b/Documentation/devicetree/bindings/mfd/cros-ec.txt
index 5f229c5f6da9..8009c3d87f33 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
diff --git a/drivers/mfd/cros_ec_spi.c b/drivers/mfd/cros_ec_spi.c
index d64d88a9e247..8e262bfb603e 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;
--
1.8.4.2