[PATCH v6 8/8] mfd: cros_ec: spi: Add delay for asserting CS

Javier Martinez Canillas
2015-06-04T08:10:28Z

From: Alexandru M Stan <amstan@chromium.org>

Some ECs need a little time for waking up before they can accept
SPI data at a high speed. This is configurable via a DT property
"google,cros-ec-spi-pre-delay".

This patch makes the cros_ec_spi driver to cause a delay before
the beginning of a SPI transaction, to make sure that the EC has
already woken up, if the property has been defined in the DTS.

Signed-off-by: Alexandru M Stan <amstan@chromium.org>
Reviewed-by: Doug Anderson <dianders@chromium.org>
Signed-off-by: Chris Zhong <zyw@rock-chips.com>
Signed-off-by: Javier Martinez Canillas <javier.martinez@collabora.co.uk>
Tested-by: Heiko Stuebner <heiko@sntech.de>
Acked-by: Lee Jones <lee.jones@linaro.org>
---

Changes since v5: None.

Changes since v4: None.

Changes since v3:
- New patch, split DT binding and driver implementation as suggested
by Lee Jones.
- Add tested-by tag from Heiko Stuebner.
- Add acked-by tag from Lee Jones.
---
drivers/mfd/cros_ec_spi.c | 21 +++++++++++++++++++--
1 file changed, 19 insertions(+), 2 deletions(-)

diff --git a/drivers/mfd/cros_ec_spi.c b/drivers/mfd/cros_ec_spi.c
index faba03e2f1ef..16f228dc243f 100644
--- a/drivers/mfd/cros_ec_spi.c
+++ b/drivers/mfd/cros_ec_spi.c
@@ -71,12 +71,15 @@
* @spi: SPI device we are connected to
* @last_transfer_ns: time that we last finished a transfer, or 0 if there
* if no record
+ * @start_of_msg_delay: used to set the delay_usecs on the spi_transfer that
+ * is sent when we want to turn on CS at the start of a transaction.
* @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 start_of_msg_delay;
unsigned int end_of_msg_delay;
};

@@ -366,7 +369,7 @@ static int cros_ec_pkt_xfer_spi(struct cros_ec_device *ec_dev,
struct ec_host_request *request;
struct ec_host_response *response;
struct cros_ec_spi *ec_spi = ec_dev->priv;
- struct spi_transfer trans;
+ struct spi_transfer trans, trans_delay;
struct spi_message msg;
int i, len;
u8 *ptr;
@@ -393,13 +396,23 @@ static int cros_ec_pkt_xfer_spi(struct cros_ec_device *ec_dev,
goto exit;
}

+ /*
+ * Leave a gap between CS assertion and clocking of data to allow the
+ * EC time to wakeup.
+ */
+ spi_message_init(&msg);
+ if (ec_spi->start_of_msg_delay) {
+ memset(&trans_delay, 0, sizeof(trans_delay));
+ trans_delay.delay_usecs = ec_spi->start_of_msg_delay;
+ spi_message_add_tail(&trans_delay, &msg);
+ }
+
/* Transmit phase - send our message */
memset(&trans, 0, sizeof(trans));
trans.tx_buf = ec_dev->dout;
trans.rx_buf = rx_buf;
trans.len = len;
trans.cs_change = 1;
- spi_message_init(&msg);
spi_message_add_tail(&trans, &msg);
ret = spi_sync(ec_spi->spi, &msg);

@@ -602,6 +615,10 @@ static void cros_ec_spi_dt_probe(struct cros_ec_spi *ec_spi, struct device *dev)
u32 val;
int ret;

+ ret = of_property_read_u32(np, "google,cros-ec-spi-pre-delay", &val);
+ if (!ret)
+ ec_spi->start_of_msg_delay = val;
+
ret = of_property_read_u32(np, "google,cros-ec-spi-msg-delay", &val);
if (!ret)
ec_spi->end_of_msg_delay = val;
--
2.1.4