clk: bcm: rpi: Turn firmware clock on/off when preparing/unpreparing

Currently, when we prepare or unprepare RPi's clocks, we don't actually
enable/disable the firmware clock. This means that
`clk_disable_unprepare()` doesn't actually change the clock state at
all, nor does it lowers the clock rate.

From the Mailbox Property Interface documentation [1], we can see that
we should use `RPI_FIRMWARE_SET_CLOCK_STATE` to set the clock state
off/on. Therefore, use `RPI_FIRMWARE_SET_CLOCK_STATE` to create a
prepare and an unprepare hook for RPi's firmware clock.

As now the clocks are actually turned off, some of them are now marked
CLK_IS_CRITICAL, as those are required to be on during the whole system
operation.

Link: https://github.com/raspberrypi/firmware/wiki/Mailbox-property-interface [1]
Signed-off-by: Maíra Canal <mcanal@igalia.com>
Reviewed-by: Stefan Wahren <wahrenst@gmx.net>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>

drivers/clk/bcm/clk-raspberrypi.c

@@ -68,6 +68,7 @@ struct raspberrypi_clk_variant {
 	char		*clkdev;
 	unsigned long	min_rate;
 	bool		minimize;
+	u32		flags;
 };
 
 static struct raspberrypi_clk_variant
@@ -75,6 +76,7 @@ raspberrypi_clk_variants[RPI_FIRMWARE_NUM_CLK_ID] = {
 	[RPI_FIRMWARE_ARM_CLK_ID] = {
 		.export = true,
 		.clkdev = "cpu0",
+		.flags = CLK_IS_CRITICAL,
 	},
 	[RPI_FIRMWARE_CORE_CLK_ID] = {
 		.export = true,
@@ -90,6 +92,12 @@ raspberrypi_clk_variants[RPI_FIRMWARE_NUM_CLK_ID] = {
 		 * always use the minimum the drivers will let us.
 		 */
 		.minimize = true,
+
+		/*
+		 * It should never be disabled as it drives the bus for
+		 * everything else.
+		 */
+		.flags = CLK_IS_CRITICAL,
 	},
 	[RPI_FIRMWARE_M2MC_CLK_ID] = {
 		.export = true,
@@ -115,6 +123,15 @@ raspberrypi_clk_variants[RPI_FIRMWARE_NUM_CLK_ID] = {
 		 * drivers will let us.
 		 */
 		.minimize = true,
+
+		/*
+		 * As mentioned above, this clock is disabled during boot,
+		 * the firmware will skip the HSM initialization, resulting
+		 * in a bus lockup. Therefore, make sure it's enabled
+		 * during boot, but after it, it can be enabled/disabled
+		 * by the driver.
+		 */
+		.flags = CLK_IGNORE_UNUSED,
 	},
 	[RPI_FIRMWARE_V3D_CLK_ID] = {
 		.export = true,
@@ -123,10 +140,12 @@ raspberrypi_clk_variants[RPI_FIRMWARE_NUM_CLK_ID] = {
 	[RPI_FIRMWARE_PIXEL_CLK_ID] = {
 		.export = true,
 		.minimize = true,
+		.flags = CLK_IS_CRITICAL,
 	},
 	[RPI_FIRMWARE_HEVC_CLK_ID] = {
 		.export = true,
 		.minimize = true,
+		.flags = CLK_IS_CRITICAL,
 	},
 	[RPI_FIRMWARE_ISP_CLK_ID] = {
 		.export = true,
@@ -135,6 +154,7 @@ raspberrypi_clk_variants[RPI_FIRMWARE_NUM_CLK_ID] = {
 	[RPI_FIRMWARE_PIXEL_BVB_CLK_ID] = {
 		.export = true,
 		.minimize = true,
+		.flags = CLK_IS_CRITICAL,
 	},
 	[RPI_FIRMWARE_VEC_CLK_ID] = {
 		.export = true,
@@ -265,7 +285,41 @@ static int raspberrypi_fw_dumb_determine_rate(struct clk_hw *hw,
 	return 0;
 }
 
+static int raspberrypi_fw_prepare(struct clk_hw *hw)
+{
+	const struct raspberrypi_clk_data *data = clk_hw_to_data(hw);
+	struct raspberrypi_clk *rpi = data->rpi;
+	u32 state = RPI_FIRMWARE_STATE_ENABLE_BIT;
+	int ret;
+
+	ret = raspberrypi_clock_property(rpi->firmware, data,
+					 RPI_FIRMWARE_SET_CLOCK_STATE, &state);
+	if (ret)
+		dev_err_ratelimited(rpi->dev,
+				    "Failed to set clock %s state to on: %d\n",
+				    clk_hw_get_name(hw), ret);
+
+	return ret;
+}
+
+static void raspberrypi_fw_unprepare(struct clk_hw *hw)
+{
+	const struct raspberrypi_clk_data *data = clk_hw_to_data(hw);
+	struct raspberrypi_clk *rpi = data->rpi;
+	u32 state = 0;
+	int ret;
+
+	ret = raspberrypi_clock_property(rpi->firmware, data,
+					 RPI_FIRMWARE_SET_CLOCK_STATE, &state);
+	if (ret)
+		dev_err_ratelimited(rpi->dev,
+				    "Failed to set clock %s state to off: %d\n",
+				    clk_hw_get_name(hw), ret);
+}
+
 static const struct clk_ops raspberrypi_firmware_clk_ops = {
+	.prepare        = raspberrypi_fw_prepare,
+	.unprepare      = raspberrypi_fw_unprepare,
 	.is_prepared	= raspberrypi_fw_is_prepared,
 	.recalc_rate	= raspberrypi_fw_get_rate,
 	.determine_rate	= raspberrypi_fw_dumb_determine_rate,
@@ -295,7 +349,7 @@ static struct clk_hw *raspberrypi_clk_register(struct raspberrypi_clk *rpi,
 	if (!init.name)
 		return ERR_PTR(-ENOMEM);
 	init.ops = &raspberrypi_firmware_clk_ops;
-	init.flags = CLK_GET_RATE_NOCACHE;
+	init.flags = variant->flags | CLK_GET_RATE_NOCACHE;
 
 	data->hw.init = &init;