irqchip/gic-v3: Allow LPIs to be disabled from the command line

For most GICv3 implementations, enabling LPIs is a one way switch.
Once they're on, there is no turning back, which completely kills
kexec (pending tables will always be live, and we can't tell the
secondary kernel where they are).

This is really annoying if you plan to use Linux as a bootloader,
as it pretty much guarantees that the secondary kernel won't be
able to use MSIs, and may even see some memory corruption. Bad.

A workaround for this unfortunate situation is to allow the kernel
not to enable LPIs, even if the feature is present in the HW. This
would allow Linux-as-a-bootloader to leave LPIs alone, and let the
secondary kernel to do whatever it wants with them.

Let's introduce a boolean "irqchip.gicv3_nolpi" command line option
that serves that purpose.

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>

1 files changed, 9 insertions, 1 deletions

diff --git a/drivers/irqchip/irq-gic-v3.c b/drivers/irqchip/irq-gic-v3.c
index 0ea02504115d..3e9eeb6cb294 100644
--- a/drivers/irqchip/irq-gic-v3.c
+++ b/drivers/irqchip/irq-gic-v3.c
@@ -613,9 +613,17 @@ static void gic_cpu_sys_reg_init(void)
 		pr_crit_once("RSS is required but GICD doesn't support it\n");
 }
 
+static bool gicv3_nolpi;
+
+static int __init gicv3_nolpi_cfg(char *buf)
+{
+	return strtobool(buf, &gicv3_nolpi);
+}
+early_param("irqchip.gicv3_nolpi", gicv3_nolpi_cfg);
+
 static int gic_dist_supports_lpis(void)
 {
-	return !!(readl_relaxed(gic_data.dist_base + GICD_TYPER) & GICD_TYPER_LPIS);
+	return !!(readl_relaxed(gic_data.dist_base + GICD_TYPER) & GICD_TYPER_LPIS) && !gicv3_nolpi;
 }
 
 static void gic_cpu_init(void)