[PATCH v3 08/15] Bluetooth: hci_bcm: Add support for LPO clock

[Chen-Yu Tsai]

The Broadcom Bluetooth controllers support a secondary LPO clock at
32.768 kHz. This external clock provides low power timing, and also
a way to detect the frequency of the main reference clock. On many
designs without NVRAM and a non-default reference clock, this must
be used or the controller will not function correctly.

Tested-by: Ondrej Jirman <meg...@megous.com>
Signed-off-by: Chen-Yu Tsai <w...@csie.org>
---
 drivers/bluetooth/hci_bcm.c | 41 ++++++++++++++++++++++++++++++++-----
 1 file changed, 36 insertions(+), 5 deletions(-)

diff --git a/drivers/bluetooth/hci_bcm.c b/drivers/bluetooth/hci_bcm.c
index 1584c95c9c34..345d728a5434 100644
--- a/drivers/bluetooth/hci_bcm.c
+++ b/drivers/bluetooth/hci_bcm.c
@@ -72,7 +72,8 @@
  * @btpu: Apple ACPI method to drive BT_REG_ON pin high ("Bluetooth Power Up")
  * @btpd: Apple ACPI method to drive BT_REG_ON pin low ("Bluetooth Power Down")
  * @txco_clk: external reference frequency clock used by Bluetooth device
- * @clk_enabled: whether @txco_clk is prepared and enabled
+ * @lpo_clk: external LPO clock used by Bluetooth device
+ * @clk_enabled: whether clocks are prepared and enabled
  * @init_speed: default baudrate of Bluetooth device;
  *     the host UART is initially set to this baudrate so that
  *     it can configure the Bluetooth device for @oper_speed
@@ -103,6 +104,7 @@ struct bcm_device {
 #endif
 
        struct clk              *txco_clk;
+       struct clk              *lpo_clk;
        bool                    clk_enabled;
 
        u32                     init_speed;
@@ -215,21 +217,34 @@ static int bcm_gpio_set_power(struct bcm_device *dev, 
bool powered)
        int err;
 
        if (powered && !dev->clk_enabled) {
-               err = clk_prepare_enable(dev->txco_clk);
+               /* LPO clock needs to be 32.768 kHz */
+               err = clk_set_rate(dev->lpo_clk, 32768);
+               if (err) {
+                       dev_err(dev->dev, "Could not set LPO clock rate\n");
+                       return err;
+               }
+
+               err = clk_prepare_enable(dev->lpo_clk);
                if (err)
                        return err;
+
+               err = clk_prepare_enable(dev->txco_clk);
+               if (err)
+                       goto err_lpo_clk_disable;
        }
 
        err = dev->set_shutdown(dev, powered);
        if (err)
-               goto err_clk_disable;
+               goto err_txco_clk_disable;
 
        err = dev->set_device_wakeup(dev, powered);
        if (err)
                goto err_revert_shutdown;
 
-       if (!powered && dev->clk_enabled)
+       if (!powered && dev->clk_enabled) {
                clk_disable_unprepare(dev->txco_clk);
+               clk_disable_unprepare(dev->lpo_clk);
+       }
 
        dev->clk_enabled = powered;
 
@@ -237,9 +252,12 @@ static int bcm_gpio_set_power(struct bcm_device *dev, bool 
powered)
 
 err_revert_shutdown:
        dev->set_shutdown(dev, !powered);
-err_clk_disable:
+err_txco_clk_disable:
        if (powered && !dev->clk_enabled)
                clk_disable_unprepare(dev->txco_clk);
+err_lpo_clk_disable:
+       if (powered && !dev->clk_enabled)
+               clk_disable_unprepare(dev->lpo_clk);
        return err;
 }
 
@@ -934,6 +952,19 @@ static int bcm_get_resources(struct bcm_device *dev)
        if (IS_ERR(dev->txco_clk))
                dev->txco_clk = NULL;
 
+       dev->lpo_clk = devm_clk_get(dev->dev, "lpo");
+       if (dev->lpo_clk == ERR_PTR(-EPROBE_DEFER))
+               return PTR_ERR(dev->lpo_clk);
+
+       if (IS_ERR(dev->lpo_clk))
+               dev->lpo_clk = NULL;
+
+       /* Check if we accidentally fetched the lpo clock twice */
+       if (dev->lpo_clk && clk_is_match(dev->lpo_clk, dev->txco_clk)) {
+               devm_clk_put(dev->dev, dev->txco_clk);
+               dev->txco_clk = NULL;
+       }
+
        dev->device_wakeup = devm_gpiod_get_optional(dev->dev, "device-wakeup",
                                                     GPIOD_OUT_LOW);
        if (IS_ERR(dev->device_wakeup))
-- 
2.20.0