[PATCH] clk: bcm: rpi: Mark VEC clock as CLK_IGNORE_UNUSED

[Maíra Canal]

On Raspberry Pi 3B, the VEC clock is used by the VideoCore firmware
display driver, which remains active until the vc4 driver loads and
sends NOTIFY_DISPLAY_DONE. If this clock is disabled during boot, a bus
lockup happens and the firmware becomes unresponsive, causing a complete
system lockup.

Mark the VEC clock with CLK_IGNORE_UNUSED so it survives the unused
clock disablement and remains available until the vc4 driver takes over
display management.

Fixes: 672299736af6 ("clk: bcm: rpi: Manage clock rate in prepare/unprepare callbacks")
Reported-by: Mark Brown <broonie at kernel.org>
Signed-off-by: Maíra Canal <mcanal at igalia.com>
---
 drivers/clk/bcm/clk-raspberrypi.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/clk/bcm/clk-raspberrypi.c b/drivers/clk/bcm/clk-raspberrypi.c
index df2d246eb6ef..f1a99de6de4f 100644
--- a/drivers/clk/bcm/clk-raspberrypi.c
+++ b/drivers/clk/bcm/clk-raspberrypi.c
@@ -160,6 +160,13 @@ raspberrypi_clk_variants[RPI_FIRMWARE_NUM_CLK_ID] = {
 	[RPI_FIRMWARE_VEC_CLK_ID] = {
 		.export = true,
 		.minimize = true,
+
+		/*
+		 * If this clock is disabled during boot, it causes a bus
+		 * lockup in RPi 3B. Therefore, make sure it's left enabled
+		 * during boot.
+		 */
+		.flags = CLK_IGNORE_UNUSED,
 	},
 	[RPI_FIRMWARE_DISP_CLK_ID] = {
 		.export = true,
-- 
2.53.0