mfd: cros_ec: spi: Add delay for asserting CS

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>
Acked-by: Olof Johansson <olof@lixom.net>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

diff --git a/drivers/mfd/cros_ec_spi.c b/drivers/mfd/cros_ec_spi.c
index faba03e2f1eff53ad6e9108f7a1f93af07f36c15..16f228dc243f3740f241a5f1315820e23f08b978 100644 (file)
--- 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;