[PATCH] irqchip/gic-v3: Allow 'dma-noncoherent' property for ITS

[Ben Dai]

Currently the ITS driver expects the hardware to report whether it is
shareable, but according to the description of the GITS_CBASER register
in the GICv3 architecture specification:
 > It is IMPLEMENTATION DEFINED whether this field has a fixed value or
 > can be programmed by software. Implementing this field with a fixed
 > value is deprecated.

It means that the hardware may expect the software to correctly configure
the access attributes of the ITS. In order to support those designs where
ITS and CPU are not in a coherent domain, allow 'dma-noncoherent' property
for ITS.

Signed-off-by: Ben Dai <ben.dai9703@xxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> (maintainer:IRQCHIP DRIVERS)
Cc: Marc Zyngier <maz@xxxxxxxxxx> (maintainer:IRQCHIP DRIVERS)
Cc: linux-kernel@xxxxxxxxxxxxxxx (open list:IRQCHIP DRIVERS)
---
 drivers/irqchip/irq-gic-v3-its.c | 24 ++++++++++++++++++------
 1 file changed, 18 insertions(+), 6 deletions(-)

diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c
index 973ede0197e3..794b14b0a6b4 100644
--- a/drivers/irqchip/irq-gic-v3-its.c
+++ b/drivers/irqchip/irq-gic-v3-its.c
@@ -5009,6 +5009,7 @@ static int __init its_probe_one(struct resource *res,
 	void __iomem *its_base;
 	u64 baser, tmp, typer;
 	struct page *page;
+	bool coherent;
 	u32 ctlr;
 	int err;
 
@@ -5087,15 +5088,25 @@ static int __init its_probe_one(struct resource *res,
 		goto out_free_tables;
 
 	baser = (virt_to_phys(its->cmd_base)	|
-		 GITS_CBASER_RaWaWb		|
-		 GITS_CBASER_InnerShareable	|
 		 (ITS_CMD_QUEUE_SZ / SZ_4K - 1)	|
 		 GITS_CBASER_VALID);
 
+	coherent = of_dma_is_coherent(to_of_node(handle));
+	if (coherent) {
+		baser |= (GITS_CBASER_RaWaWb | GITS_CBASER_InnerShareable);
+	} else {
+		baser |= GITS_CBASER_nC;
+		its->flags |= ITS_FLAGS_CMDQ_NEEDS_FLUSHING;
+	}
+
 	gits_write_cbaser(baser, its->base + GITS_CBASER);
-	tmp = gits_read_cbaser(its->base + GITS_CBASER);
 
-	if ((tmp ^ baser) & GITS_CBASER_SHAREABILITY_MASK) {
+	if (coherent) {
+		tmp = gits_read_cbaser(its->base + GITS_CBASER);
+
+		if ((tmp ^ baser) & GITS_CBASER_SHAREABILITY_MASK)
+			its->flags |= ITS_FLAGS_CMDQ_NEEDS_FLUSHING;
+
 		if (!(tmp & GITS_CBASER_SHAREABILITY_MASK)) {
 			/*
 			 * The HW reports non-shareable, we must
@@ -5107,10 +5118,11 @@ static int __init its_probe_one(struct resource *res,
 			baser |= GITS_CBASER_nC;
 			gits_write_cbaser(baser, its->base + GITS_CBASER);
 		}
-		pr_info("ITS: using cache flushing for cmd queue\n");
-		its->flags |= ITS_FLAGS_CMDQ_NEEDS_FLUSHING;
 	}
 
+	if (its->flags & ITS_FLAGS_CMDQ_NEEDS_FLUSHING)
+		pr_info("ITS: using cache flushing for cmd queue\n");
+
 	gits_write_cwriter(0, its->base + GITS_CWRITER);
 	ctlr = readl_relaxed(its->base + GITS_CTLR);
 	ctlr |= GITS_CTLR_ENABLE;
-- 
2.34.1