irqchip/gic-v3-its: Allow use of pre-programmed LPI tables

In order to cope with kexec and GICv3, let's try and spot when
we're booting with LPIs already enabled, and the tables already
programmed into the redistributors.

This code is currently guarded by a predicate that is always false,
meaning this is not functionnal just yet.

Reviewed-by: Julien Thierry <julien.thierry@arm.com>
Tested-by: Jeremy Linton <jeremy.linton@arm.com>
Tested-by: Bhupesh Sharma <bhsharma@redhat.com>
Tested-by: Lei Zhang <zhang.lei@jp.fujitsu.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>

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

@@ -52,6 +52,7 @@
 #define ITS_FLAGS_SAVE_SUSPEND_STATE		(1ULL << 3)
 
 #define RDIST_FLAGS_PROPBASE_NEEDS_FLUSHING	(1 << 0)
+#define RDIST_FLAGS_RD_TABLES_PREALLOCATED	(1 << 1)
 
 static u32 lpi_id_bits;
 
@@ -1628,19 +1629,33 @@ static void its_free_prop_table(struct page *prop_page)
 
 static int __init its_setup_lpi_prop_table(void)
 {
-	struct page *page;
+	if (gic_rdists->flags & RDIST_FLAGS_RD_TABLES_PREALLOCATED) {
+		u64 val;
 
-	lpi_id_bits = min_t(u32, GICD_TYPER_ID_BITS(gic_rdists->gicd_typer),
-				ITS_MAX_LPI_NRBITS);
-	page = its_allocate_prop_table(GFP_NOWAIT);
-	if (!page) {
-		pr_err("Failed to allocate PROPBASE\n");
-		return -ENOMEM;
+		val = gicr_read_propbaser(gic_data_rdist_rd_base() + GICR_PROPBASER);
+		lpi_id_bits = (val & GICR_PROPBASER_IDBITS_MASK) + 1;
+
+		gic_rdists->prop_table_pa = val & GENMASK_ULL(51, 12);
+		gic_rdists->prop_table_va = memremap(gic_rdists->prop_table_pa,
+						     LPI_PROPBASE_SZ,
+						     MEMREMAP_WB);
+		gic_reset_prop_table(gic_rdists->prop_table_va);
+	} else {
+		struct page *page;
+
+		lpi_id_bits = min_t(u32,
+				    GICD_TYPER_ID_BITS(gic_rdists->gicd_typer),
+				    ITS_MAX_LPI_NRBITS);
+		page = its_allocate_prop_table(GFP_NOWAIT);
+		if (!page) {
+			pr_err("Failed to allocate PROPBASE\n");
+			return -ENOMEM;
+		}
+
+		gic_rdists->prop_table_pa = page_to_phys(page);
+		gic_rdists->prop_table_va = page_address(page);
 	}
 
-	gic_rdists->prop_table_pa = page_to_phys(page);
-	gic_rdists->prop_table_va = page_address(page);
-
 	pr_info("GICv3: using LPI property table @%pa\n",
 		&gic_rdists->prop_table_pa);
 
@@ -1948,10 +1963,27 @@ static void its_free_pending_table(struct page *pt)
 	free_pages((unsigned long)page_address(pt), get_order(LPI_PENDBASE_SZ));
 }
 
+static bool enabled_lpis_allowed(void)
+{
+	return false;
+}
+
 static int __init allocate_lpi_tables(void)
 {
+	u64 val;
 	int err, cpu;
 
+	/*
+	 * If LPIs are enabled while we run this from the boot CPU,
+	 * flag the RD tables as pre-allocated if the stars do align.
+	 */
+	val = readl_relaxed(gic_data_rdist_rd_base() + GICR_CTLR);
+	if ((val & GICR_CTLR_ENABLE_LPIS) && enabled_lpis_allowed()) {
+		gic_rdists->flags |= (RDIST_FLAGS_RD_TABLES_PREALLOCATED |
+				      RDIST_FLAGS_PROPBASE_NEEDS_FLUSHING);
+		pr_info("GICv3: Using preallocated redistributor tables\n");
+	}
+
 	err = its_setup_lpi_prop_table();
 	if (err)
 		return err;
@@ -1986,6 +2018,18 @@ static void its_cpu_init_lpis(void)
 	if (gic_data_rdist()->lpi_enabled)
 		return;
 
+	val = readl_relaxed(rbase + GICR_CTLR);
+	if ((gic_rdists->flags & RDIST_FLAGS_RD_TABLES_PREALLOCATED) &&
+	    (val & GICR_CTLR_ENABLE_LPIS)) {
+		paddr = gicr_read_pendbaser(rbase + GICR_PENDBASER);
+		paddr &= GENMASK_ULL(51, 16);
+
+		its_free_pending_table(gic_data_rdist()->pend_page);
+		gic_data_rdist()->pend_page = NULL;
+
+		goto out;
+	}
+
 	pend_page = gic_data_rdist()->pend_page;
 	paddr = page_to_phys(pend_page);
 
@@ -2040,9 +2084,11 @@ static void its_cpu_init_lpis(void)
 
 	/* Make sure the GIC has seen the above */
 	dsb(sy);
+out:
 	gic_data_rdist()->lpi_enabled = true;
-	pr_info("GICv3: CPU%d: using LPI pending table @%pa\n",
+	pr_info("GICv3: CPU%d: using %s LPI pending table @%pa\n",
 		smp_processor_id(),
+		gic_data_rdist()->pend_page ? "allocated" : "reserved",
 		&paddr);
 }
 
@@ -3535,8 +3581,11 @@ static int redist_disable_lpis(void)
 	 * If coming via a CPU hotplug event, we don't need to disable
 	 * LPIs before trying to re-enable them. They are already
 	 * configured and all is well in the world.
+	 *
+	 * If running with preallocated tables, there is nothing to do.
 	 */
-	if (gic_data_rdist()->lpi_enabled)
+	if (gic_data_rdist()->lpi_enabled ||
+	    (gic_rdists->flags & RDIST_FLAGS_RD_TABLES_PREALLOCATED))
 		return 0;
 
 	/*