[PATCH 1/3] arm64: Disable GiC priorities on Mediatek devices w/ firmware issues

Douglas Anderson
2023-10-06T22:16:49Z

In commit 44bd78dd2b88 ("irqchip/gic-v3: Disable pseudo NMIs on
Mediatek devices w/ firmware issues") we added a method for detecting
Mediatek devices with broken firmware and disabled pseudo-NMI. While
that worked, it didn't address the problem at a deep enough level.

The fundamental issue with this broken firmware is that it's not
saving and restoring several important GICR registers. The current
list is believed to be:
* GICR_NUM_IPRIORITYR
* GICR_CTLR
* GICR_ISPENDR0
* GICR_ISACTIVER0
* GICR_NSACR

Pseudo-NMI didn't work because it was the only thing (currently) in
the kernel that relied on the broken registers, so forcing pseudo-NMI
off was an effective fix. However, it could be observed that calling
system_uses_irq_prio_masking() on these systems still returned
"true". That caused confusion and led to the need for
commit a07a59415217 ("arm64: smp: avoid NMI IPIs with broken MediaTek
FW"). It's worried that the incorrect value returned by
system_uses_irq_prio_masking() on these systems will continue to
confuse future developers.

Let's fix the issue a little more completely by disabling IRQ
priorities at a deeper level in the kernel. Once we do this we can
revert some of the other bits of code dealing with this quirk.

Signed-off-by: Douglas Anderson <dianders@chromium.org>
---

arch/arm64/kernel/cpufeature.c | 21 +++++++++++++++++++++
1 file changed, 21 insertions(+)

diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 2806a2850e78..e35efab8efa9 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -2094,9 +2094,30 @@ static int __init early_enable_pseudo_nmi(char *p)
}
early_param("irqchip.gicv3_pseudo_nmi", early_enable_pseudo_nmi);

+static bool are_gic_priorities_broken(void)
+{
+ bool is_broken = false;
+ struct device_node *np;
+
+ /*
+ * Detect broken Mediatek firmware that doesn't properly save and
+ * restore GIC priorities.
+ */
+ np = of_find_compatible_node(NULL, NULL, "arm,gic-v3");
+ if (np) {
+ is_broken = of_property_read_bool(np, "mediatek,broken-save-restore-fw");
+ of_node_put(np);
+ }
+
+ return is_broken;
+}
+
static bool can_use_gic_priorities(const struct arm64_cpu_capabilities *entry,
int scope)
{
+ if (are_gic_priorities_broken())
+ return false;
+
/*
* ARM64_HAS_GIC_CPUIF_SYSREGS has a lower index, and is a boot CPU
* feature, so will be detected earlier.
--
2.42.0.609.gbb76f46606-goog