greybus: arche-platform: Add support for SPI bus sharing for Mihi

In case of Mihi, SPI bus is shared between APB1 and APB2
SPI ROMs, so their FW flashing must be sequential and
arche-platform driver should make sure that they are mutual
exclusive in nature.

So this patch adds certain restrictions to the user of the
arche-platform driver,

 - User can no longer flash APB1 and APB2 SPI ROM in parallel
 - SPI bus becomes an resource, so user must claim it by moving
   respective APB device into FW_FLASHING mode and release it
   by exiting FW_FLASHING mode. User can exit FW_FLASHING mode by
   switching to any other modes (ACTIVE, OFF, STANDBY).
 - If APB1 is in FW_FLASHING mode, APB2 can no longer enter into
   FW_FLASHING mode. User will get -EBUSY.

Having said that, while APB1 is into FW_FLASHING mode,
APB2 can independently boot from its own SPI ROM.

Testing Done: Tested by simulating usecase on EVT2.
 - Made sure that APB1 and APB2 FW_FLASHING mode is mutual exclusive
   in nature. Confirmed that an attempt on second device return -EBUSY.
 - Added simulating code, where printed state of dummy gpio for
   spi-en and verified that it shows right pin status for both APBs

Signed-off-by: Vaibhav Hiremath <vaibhav.hiremath@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>

1 files changed, 7 insertions, 18 deletions

diff --git a/drivers/staging/greybus/arche-platform.c b/drivers/staging/greybus/arche-platform.c
index adec1fdcb5bb..9d9048e6aed3 100644
--- a/drivers/staging/greybus/arche-platform.c
+++ b/drivers/staging/greybus/arche-platform.c
@@ -215,18 +215,6 @@ static int apb_cold_boot(struct device *dev, void *data)
 	return 0;
 }
 
-static int apb_fw_flashing_state(struct device *dev, void *data)
-{
-	int ret;
-
-	ret = apb_ctrl_fw_flashing(dev);
-	if (ret)
-		dev_warn(dev, "failed to switch to fw flashing state\n");
-
-	/*Child nodes are independent, so do not exit coldboot operation */
-	return 0;
-}
-
 static int apb_poweroff(struct device *dev, void *data)
 {
 	apb_ctrl_poweroff(dev);
@@ -485,17 +473,18 @@ retry:
 		if (arche_pdata->state == ARCHE_PLATFORM_STATE_FW_FLASHING)
 			goto exit;
 
-		/* First we want to make sure we power off everything
-		 * and then enter FW flashing state */
-		device_for_each_child(arche_pdata->dev, NULL, apb_poweroff);
-
+		/*
+		 * Here we only control SVC.
+		 *
+		 * In case of FW_FLASHING mode we do not want to control
+		 * APBs, as in case of V2, SPI bus is shared between both
+		 * the APBs. So let user chose which APB he wants to flash.
+		 */
 		arche_platform_poweroff_seq(arche_pdata);
 
 		ret = arche_platform_fw_flashing_seq(arche_pdata);
 		if (ret)
 			goto exit;
-
-		device_for_each_child(arche_pdata->dev, NULL, apb_fw_flashing_state);
 	} else {
 		dev_err(arche_pdata->dev, "unknown state\n");
 		ret = -EINVAL;