[PATCH/RFC 1/5] clk: shmobile: mstp: Never disable INTC-SYS

[Geert Uytterhoeven <geert+renesas@glider.be>]

INTC-SYS is the module clock for the GIC.  Accessing the GIC while it is
disabled causes:

    Unhandled fault: asynchronous external abort (0x1211) at 0x00000000

Currently, the GIC driver cannot enable its module clock for several
reasons:
  - It does not use a platform device, so Runtime PM is not an option,
  - gic_of_init() runs before any clocks are registered, so it cannot
    explicitly enable the clock,
  - gic_of_init() cannot return -EPROBE_DEFER, as IRQCHIP_DECLARE()
    doesn't support deferred probing.

Hence we have to keep on relying on the boot loader for enabling the
module clock.

To prevent the module clock from being disabled when the CCF core thinks
it is unused, and thus causing a system lock-up, add a quirk to the MSTP
clock driver to make sure the module clock is never disabled.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
---
 drivers/clk/shmobile/clk-mstp.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/clk/shmobile/clk-mstp.c b/drivers/clk/shmobile/clk-mstp.c
index 2d2fe773ac8168f9..742af84735a07450 100644
--- a/drivers/clk/shmobile/clk-mstp.c
+++ b/drivers/clk/shmobile/clk-mstp.c
@@ -62,6 +62,12 @@ static int cpg_mstp_clock_endisable(struct clk_hw *hw, bool enable)
 	unsigned int i;
 	u32 value;
 
+	/* INTC-SYS is the module clock of the GIC, and must not be disabled */
+	if (!enable && !strcmp(__clk_get_name(hw->clk), "intc-sys")) {
+		pr_debug("MSTP %pC skipping disable\n", hw->clk);
+		return 0;
+	}
+
 	spin_lock_irqsave(&group->lock, flags);
 
 	value = clk_readl(group->smstpcr);
-- 
1.9.1