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, 43 insertions, 0 deletions

diff --git a/drivers/staging/greybus/arche-apb-ctrl.c b/drivers/staging/greybus/arche-apb-ctrl.c
index 049d496a41f4..59d9d422cf04 100644
--- a/drivers/staging/greybus/arche-apb-ctrl.c
+++ b/drivers/staging/greybus/arche-apb-ctrl.c
@@ -42,6 +42,10 @@ struct arche_apb_ctrl_drvdata {
 
 	struct pinctrl *pinctrl;
 	struct pinctrl_state *pin_default;
+
+	/* V2: SPI Bus control  */
+	int spi_en_gpio;
+	bool spi_en_polarity_high;
 };
 
 /*
@@ -73,6 +77,10 @@ static int coldboot_seq(struct platform_device *pdev)
 	/* Hold APB in reset state */
 	assert_reset(apb->resetn_gpio);
 
+	if (apb->state == ARCHE_PLATFORM_STATE_FW_FLASHING &&
+			gpio_is_valid(apb->spi_en_gpio))
+		devm_gpio_free(dev, apb->spi_en_gpio);
+
 	/* Enable power to APB */
 	if (!IS_ERR(apb->vcore)) {
 		ret = regulator_enable(apb->vcore);
@@ -128,6 +136,23 @@ static int fw_flashing_seq(struct platform_device *pdev)
 		return ret;
 	}
 
+	if (gpio_is_valid(apb->spi_en_gpio)) {
+		unsigned long flags;
+
+		if (apb->spi_en_polarity_high)
+			flags = GPIOF_OUT_INIT_HIGH;
+		else
+			flags = GPIOF_OUT_INIT_LOW;
+
+		ret = devm_gpio_request_one(dev, apb->spi_en_gpio,
+				flags, "apb_spi_en");
+		if (ret) {
+			dev_err(dev, "Failed requesting SPI bus en gpio %d\n",
+				apb->spi_en_gpio);
+			return ret;
+		}
+	}
+
 	/* for flashing device should be in reset state */
 	assert_reset(apb->resetn_gpio);
 	apb->state = ARCHE_PLATFORM_STATE_FW_FLASHING;
@@ -137,6 +162,7 @@ static int fw_flashing_seq(struct platform_device *pdev)
 
 static int standby_boot_seq(struct platform_device *pdev)
 {
+	struct device *dev = &pdev->dev;
 	struct arche_apb_ctrl_drvdata *apb = platform_get_drvdata(pdev);
 
 	if (apb->init_disabled)
@@ -147,6 +173,10 @@ static int standby_boot_seq(struct platform_device *pdev)
 			apb->state == ARCHE_PLATFORM_STATE_OFF)
 		return 0;
 
+	if (apb->state == ARCHE_PLATFORM_STATE_FW_FLASHING &&
+			gpio_is_valid(apb->spi_en_gpio))
+		devm_gpio_free(dev, apb->spi_en_gpio);
+
 	/*
 	 * As per WDM spec, do nothing
 	 *
@@ -162,11 +192,16 @@ static int standby_boot_seq(struct platform_device *pdev)
 
 static void poweroff_seq(struct platform_device *pdev)
 {
+	struct device *dev = &pdev->dev;
 	struct arche_apb_ctrl_drvdata *apb = platform_get_drvdata(pdev);
 
 	if (apb->init_disabled || apb->state == ARCHE_PLATFORM_STATE_OFF)
 		return;
 
+	if (apb->state == ARCHE_PLATFORM_STATE_FW_FLASHING &&
+			gpio_is_valid(apb->spi_en_gpio))
+		devm_gpio_free(dev, apb->spi_en_gpio);
+
 	/* disable the clock */
 	if (gpio_is_valid(apb->clk_en_gpio))
 		gpio_set_value(apb->clk_en_gpio, 0);
@@ -369,6 +404,14 @@ static int apb_ctrl_get_devtree_data(struct platform_device *pdev,
 		return PTR_ERR(apb->pin_default);
 	}
 
+	/* Only applicable for platform >= V2 */
+	apb->spi_en_gpio = of_get_named_gpio(np, "spi-en-gpio", 0);
+	if (apb->spi_en_gpio >= 0) {
+		if (of_property_read_bool(pdev->dev.of_node,
+					"spi-en-active-high"))
+			apb->spi_en_polarity_high = true;
+	}
+
 	return 0;
 }