irqchip/gic-v3: Disable pseudo NMIs on Mediatek devices w/ firmware issues

Some Chromebooks with Mediatek SoCs have a problem where the firmware
doesn't properly save/restore certain GICR registers. Newer
Chromebooks should fix this issue and we may be able to do firmware
updates for old Chromebooks. At the moment, the only known issue with
these Chromebooks is that we can't enable "pseudo NMIs" since the
priority register can be lost. Enabling "pseudo NMIs" on Chromebooks
with the problematic firmware causes crashes and freezes.

Let's detect devices with this problem and then disable "pseudo NMIs"
on them. We'll detect the problem by looking for the presence of the
"mediatek,broken-save-restore-fw" property in the GIC device tree
node. Any devices with fixed firmware will not have this property.

Our detection plan works because we never bake a Chromebook's device
tree into firmware. Instead, device trees are always bundled with the
kernel. We'll update the device trees of all affected Chromebooks and
then we'll never enable "pseudo NMI" on a kernel that is bundled with
old device trees. When a firmware update is shipped that fixes this
issue it will know to patch the device tree to remove the property.

In order to make this work, the quick detection mechanism of the GICv3
code is extended to be able to look for properties in addition to
looking at "compatible".
Reviewed-by: Julius Werner <jwerner@chromium.org>
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20230515131353.v2.2.I88dc0a0eb1d9d537de61604cd8994ecc55c0cac1@changeid

drivers/irqchip/irq-gic-common.c

@@ -16,7 +16,11 @@ void gic_enable_of_quirks(const struct device_node *np,
 			  const struct gic_quirk *quirks, void *data)
 {
 	for (; quirks->desc; quirks++) {
-		if (!of_device_is_compatible(np, quirks->compatible))
+		if (quirks->compatible &&
+		    !of_device_is_compatible(np, quirks->compatible))
+			continue;
+		if (quirks->property &&
+		    !of_property_read_bool(np, quirks->property))
 			continue;
 		if (quirks->init(data))
 			pr_info("GIC: enabling workaround for %s\n",
@@ -28,7 +32,7 @@ void gic_enable_quirks(u32 iidr, const struct gic_quirk *quirks,
 		void *data)
 {
 	for (; quirks->desc; quirks++) {
-		if (quirks->compatible)
+		if (quirks->compatible || quirks->property)
 			continue;
 		if (quirks->iidr != (quirks->mask & iidr))
 			continue;

drivers/irqchip/irq-gic-common.h

@@ -13,6 +13,7 @@
 struct gic_quirk {
 	const char *desc;
 	const char *compatible;
+	const char *property;
 	bool (*init)(void *data);
 	u32 iidr;
 	u32 mask;

drivers/irqchip/irq-gic-v3.c

@@ -39,6 +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 GIC_IRQ_TYPE_PARTITION	(GIC_IRQ_TYPE_LPI + 1)
 
@@ -1720,6 +1721,15 @@ 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;
@@ -1792,6 +1802,11 @@ static const struct gic_quirk gic_quirks[] = {
 		.compatible = "qcom,msm8996-gic-v3",
 		.init	= gic_enable_quirk_msm8996,
 	},
+	{
+		.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,
@@ -1834,6 +1849,11 @@ 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;
+	}
+
 	ppi_nmi_refs = kcalloc(gic_data.ppi_nr, sizeof(*ppi_nmi_refs), GFP_KERNEL);
 	if (!ppi_nmi_refs)
 		return;