irqchip/gic-v3-its: Unconditionally save/restore the ITS state on suspend

On systems without HW-based collections (i.e. anything except GIC-500),
we rely on firmware to perform the ITS save/restore. This doesn't
really work, as although FW can properly save everything, it cannot
fully restore the state of the command queue (the read-side is reset
to the head of the queue). This results in the ITS consuming previously
processed commands, potentially corrupting the state.

Instead, let's always save the ITS state on suspend, disabling it in the
process, and restore the full state on resume. This saves us from broken
FW as long as it doesn't enable the ITS by itself (for which we can't do
anything).

This amounts to simply dropping the ITS_FLAGS_SAVE_SUSPEND_STATE.

Signed-off-by: Xu Qiang <[e-mail]>
[maz: added warning on resume, rewrote commit message]
Signed-off-by: Marc Zyngier <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

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

···
 #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)
 #define RDIST_FLAGS_RD_TABLES_PREALLOCATED	(1 << 1)
···
 	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) {
 		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);
···
 		void __iomem *base;
 		int i;
 
-		if (!(its->flags & ITS_FLAGS_SAVE_SUSPEND_STATE))
-			continue;
-
 		base = its->base;
 
 		/*
···
 		 * don't restore it since writing to CBASER or BASER<n>
 		 * registers is undefined according to the GIC v3 ITS
 		 * Specification.
+		 *
+		 * Firmware resuming with the ITS enabled is terminally broken.
 		 */
+		WARN_ON(readl_relaxed(base + GITS_CTLR) & GITS_CTLR_ENABLE);
 		ret = its_force_quiescent(base);
 		if (ret) {
 			pr_err("ITS@%pa: failed to quiesce on resume: %d\n",
···
 	if (is_v4(its))
 		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)