[PATCH v2 1/2] arm64: Move Mediatek GIC quirk handling from irqchip to core

[Douglas Anderson]

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.

This includes a partial revert of commit 44bd78dd2b88
("irqchip/gic-v3: Disable pseudo NMIs on Mediatek devices w/ firmware
issues"). This isn't a full revert because it leaves some of the
changes to the "quirks" structure around in case future code needs it.

Suggested-by: Mark Rutland <mark.rutland@xxxxxxx>
Signed-off-by: Douglas Anderson <dianders@xxxxxxxxxxxx>
---

Changes in v2:
- Just detect the quirk once at init time.
- Fixed typo in subject: s/GiC/GIC.
- Squash in ("Remove Mediatek pseudo-NMI firmware quirk handling").

 arch/arm64/kernel/cpufeature.c | 46 ++++++++++++++++++++++++++++------
 drivers/irqchip/irq-gic-v3.c   | 22 +---------------
 2 files changed, 39 insertions(+), 29 deletions(-)

diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index f6b2e2906fc9..928124ea2e96 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -999,6 +999,37 @@ static void init_32bit_cpu_features(struct cpuinfo_32bit *info)
 	init_cpu_ftr_reg(SYS_MVFR2_EL1, info->reg_mvfr2);
 }
 
+#ifdef CONFIG_ARM64_PSEUDO_NMI
+static bool enable_pseudo_nmi;
+
+static int __init early_enable_pseudo_nmi(char *p)
+{
+	return kstrtobool(p, &enable_pseudo_nmi);
+}
+early_param("irqchip.gicv3_pseudo_nmi", early_enable_pseudo_nmi);
+
+static __init void detect_system_supports_pseudo_nmi(void)
+{
+	struct device_node *np;
+
+	if (!enable_pseudo_nmi)
+		return;
+
+	/*
+	 * 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 && of_property_read_bool(np, "mediatek,broken-save-restore-fw")) {
+		pr_info("Pseudo-NMI disabled due to Mediatek Chromebook GICR save problem\n");
+		enable_pseudo_nmi = false;
+	}
+	of_node_put(np);
+}
+#else /* CONFIG_ARM64_PSEUDO_NMI */
+static inline void detect_system_supports_pseudo_nmi(void) { }
+#endif
+
 void __init init_cpu_features(struct cpuinfo_arm64 *info)
 {
 	/* Before we start using the tables, make sure it is sorted */
@@ -1057,6 +1088,13 @@ void __init init_cpu_features(struct cpuinfo_arm64 *info)
 	 */
 	init_cpucap_indirect_list();
 
+	/*
+	 * Detect broken pseudo-NMI. Must be called _before_ the call to
+	 * setup_boot_cpu_capabilities() since it interacts with
+	 * can_use_gic_priorities().
+	 */
+	detect_system_supports_pseudo_nmi();
+
 	/*
 	 * Detect and enable early CPU capabilities based on the boot CPU,
 	 * after we have initialised the CPU feature infrastructure.
@@ -2085,14 +2123,6 @@ static void cpu_enable_e0pd(struct arm64_cpu_capabilities const *cap)
 #endif /* CONFIG_ARM64_E0PD */
 
 #ifdef CONFIG_ARM64_PSEUDO_NMI
-static bool enable_pseudo_nmi;
-
-static int __init early_enable_pseudo_nmi(char *p)
-{
-	return kstrtobool(p, &enable_pseudo_nmi);
-}
-early_param("irqchip.gicv3_pseudo_nmi", early_enable_pseudo_nmi);
-
 static bool can_use_gic_priorities(const struct arm64_cpu_capabilities *entry,
 				   int scope)
 {
diff --git a/drivers/irqchip/irq-gic-v3.c b/drivers/irqchip/irq-gic-v3.c
index 68d11ccee441..1ba674367ee3 100644
--- a/drivers/irqchip/irq-gic-v3.c
+++ b/drivers/irqchip/irq-gic-v3.c
@@ -39,8 +39,7 @@
 
 #define FLAGS_WORKAROUND_GICR_WAKER_MSM8996	(1ULL << 0)
 #define FLAGS_WORKAROUND_CAVIUM_ERRATUM_38539	(1ULL << 1)
-#define FLAGS_WORKAROUND_MTK_GICR_SAVE		(1ULL << 2)
-#define FLAGS_WORKAROUND_ASR_ERRATUM_8601001	(1ULL << 3)
+#define FLAGS_WORKAROUND_ASR_ERRATUM_8601001	(1ULL << 2)
 
 #define GIC_IRQ_TYPE_PARTITION	(GIC_IRQ_TYPE_LPI + 1)
 
@@ -1779,15 +1778,6 @@ static bool gic_enable_quirk_msm8996(void *data)
 	return true;
 }
 
-static bool gic_enable_quirk_mtk_gicr(void *data)
-{
-	struct gic_chip_data *d = data;
-
-	d->flags |= FLAGS_WORKAROUND_MTK_GICR_SAVE;
-
-	return true;
-}
-
 static bool gic_enable_quirk_cavium_38539(void *data)
 {
 	struct gic_chip_data *d = data;
@@ -1888,11 +1878,6 @@ static const struct gic_quirk gic_quirks[] = {
 		.compatible = "asr,asr8601-gic-v3",
 		.init	= gic_enable_quirk_asr8601,
 	},
-	{
-		.desc	= "GICv3: Mediatek Chromebook GICR save problem",
-		.property = "mediatek,broken-save-restore-fw",
-		.init	= gic_enable_quirk_mtk_gicr,
-	},
 	{
 		.desc	= "GICv3: HIP06 erratum 161010803",
 		.iidr	= 0x0204043b,
@@ -1959,11 +1944,6 @@ static void gic_enable_nmi_support(void)
 	if (!gic_prio_masking_enabled())
 		return;
 
-	if (gic_data.flags & FLAGS_WORKAROUND_MTK_GICR_SAVE) {
-		pr_warn("Skipping NMI enable due to firmware issues\n");
-		return;
-	}
-
 	rdist_nmi_refs = kcalloc(gic_data.ppi_nr + SGI_NR,
 				 sizeof(*rdist_nmi_refs), GFP_KERNEL);
 	if (!rdist_nmi_refs)
-- 
2.42.0.869.gea05f2083d-goog