irqchip/gic-v3-its: Add ability to save/restore ITS state

Some platforms power off GIC logic in suspend, so we need to
save/restore state. The distributor and redistributor registers need
to be handled in firmware code due to access permissions on those
registers, but the ITS registers can be restored in the kernel.

We limit this to systems where the ITS collections are implemented
in HW (as opposed to being backed by memory tables), as they are
the only ones that cannot be dealt with by the firmware.

Signed-off-by: Derek Basehore <dbasehore@chromium.org>
[maz: fixed changelog, dropped DT property, limited to HCC being >0]
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>

drivers/irqchip/irq-gic-v3-its.c

@@ -33,6 +33,7 @@
 #include <linux/of_platform.h>
 #include <linux/percpu.h>
 #include <linux/slab.h>
+#include <linux/syscore_ops.h>
 
 #include <linux/irqchip.h>
 #include <linux/irqchip/arm-gic-v3.h>
@@ -46,6 +47,7 @@
 #define ITS_FLAGS_CMDQ_NEEDS_FLUSHING		(1ULL << 0)
 #define ITS_FLAGS_WORKAROUND_CAVIUM_22375	(1ULL << 1)
 #define ITS_FLAGS_WORKAROUND_CAVIUM_23144	(1ULL << 2)
+#define ITS_FLAGS_SAVE_SUSPEND_STATE		(1ULL << 3)
 
 #define RDIST_FLAGS_PROPBASE_NEEDS_FLUSHING	(1 << 0)
 
@@ -101,6 +103,8 @@ struct its_node {
 	struct its_collection	*collections;
 	struct fwnode_handle	*fwnode_handle;
 	u64			(*get_msi_base)(struct its_device *its_dev);
+	u64			cbaser_save;
+	u32			ctlr_save;
 	struct list_head	its_device_list;
 	u64			flags;
 	unsigned long		list_nr;
@@ -3042,6 +3046,104 @@ static void its_enable_quirks(struct its_node *its)
 	gic_enable_quirks(iidr, its_quirks, its);
 }
 
+static int its_save_disable(void)
+{
+	struct its_node *its;
+	int err = 0;
+
+	spin_lock(&its_lock);
+	list_for_each_entry(its, &its_nodes, entry) {
+		void __iomem *base;
+
+		if (!(its->flags & ITS_FLAGS_SAVE_SUSPEND_STATE))
+			continue;
+
+		base = its->base;
+		its->ctlr_save = readl_relaxed(base + GITS_CTLR);
+		err = its_force_quiescent(base);
+		if (err) {
+			pr_err("ITS@%pa: failed to quiesce: %d\n",
+			       &its->phys_base, err);
+			writel_relaxed(its->ctlr_save, base + GITS_CTLR);
+			goto err;
+		}
+
+		its->cbaser_save = gits_read_cbaser(base + GITS_CBASER);
+	}
+
+err:
+	if (err) {
+		list_for_each_entry_continue_reverse(its, &its_nodes, entry) {
+			void __iomem *base;
+
+			if (!(its->flags & ITS_FLAGS_SAVE_SUSPEND_STATE))
+				continue;
+
+			base = its->base;
+			writel_relaxed(its->ctlr_save, base + GITS_CTLR);
+		}
+	}
+	spin_unlock(&its_lock);
+
+	return err;
+}
+
+static void its_restore_enable(void)
+{
+	struct its_node *its;
+	int ret;
+
+	spin_lock(&its_lock);
+	list_for_each_entry(its, &its_nodes, entry) {
+		void __iomem *base;
+		int i;
+
+		if (!(its->flags & ITS_FLAGS_SAVE_SUSPEND_STATE))
+			continue;
+
+		base = its->base;
+
+		/*
+		 * Make sure that the ITS is disabled. If it fails to quiesce,
+		 * don't restore it since writing to CBASER or BASER<n>
+		 * registers is undefined according to the GIC v3 ITS
+		 * Specification.
+		 */
+		ret = its_force_quiescent(base);
+		if (ret) {
+			pr_err("ITS@%pa: failed to quiesce on resume: %d\n",
+			       &its->phys_base, ret);
+			continue;
+		}
+
+		gits_write_cbaser(its->cbaser_save, base + GITS_CBASER);
+
+		/*
+		 * Writing CBASER resets CREADR to 0, so make CWRITER and
+		 * cmd_write line up with it.
+		 */
+		its->cmd_write = its->cmd_base;
+		gits_write_cwriter(0, base + GITS_CWRITER);
+
+		/* Restore GITS_BASER from the value cache. */
+		for (i = 0; i < GITS_BASER_NR_REGS; i++) {
+			struct its_baser *baser = &its->tables[i];
+
+			if (!(baser->val & GITS_BASER_VALID))
+				continue;
+
+			its_write_baser(its, baser, baser->val);
+		}
+		writel_relaxed(its->ctlr_save, base + GITS_CTLR);
+	}
+	spin_unlock(&its_lock);
+}
+
+static struct syscore_ops its_syscore_ops = {
+	.suspend = its_save_disable,
+	.resume = its_restore_enable,
+};
+
 static int its_init_domain(struct fwnode_handle *handle, struct its_node *its)
 {
 	struct irq_domain *inner_domain;
@@ -3261,6 +3363,9 @@ static int __init its_probe_one(struct resource *res,
 		ctlr |= GITS_CTLR_ImDe;
 	writel_relaxed(ctlr, its->base + GITS_CTLR);
 
+	if (GITS_TYPER_HCC(typer))
+		its->flags |= ITS_FLAGS_SAVE_SUSPEND_STATE;
+
 	err = its_init_domain(handle, its);
 	if (err)
 		goto out_free_tables;
@@ -3517,5 +3622,7 @@ int __init its_init(struct fwnode_handle *handle, struct rdists *rdists,
 		}
 	}
 
+	register_syscore_ops(&its_syscore_ops);
+
 	return 0;
 }

include/linux/irqchip/arm-gic-v3.h

@@ -312,7 +312,8 @@
 #define GITS_TYPER_DEVBITS_SHIFT	13
 #define GITS_TYPER_DEVBITS(r)		((((r) >> GITS_TYPER_DEVBITS_SHIFT) & 0x1f) + 1)
 #define GITS_TYPER_PTA			(1UL << 19)
-#define GITS_TYPER_HWCOLLCNT_SHIFT	24
+#define GITS_TYPER_HCC_SHIFT		24
+#define GITS_TYPER_HCC(r)		(((r) >> GITS_TYPER_HCC_SHIFT) & 0xff)
 #define GITS_TYPER_VMOVP		(1ULL << 37)
 
 #define GITS_IIDR_REV_SHIFT		12