[PATCH v4] irqchip/gic-v3-its: Flush ITS tables before writing GITS_BASER<n> registers in non-coherent GIC designs.

[Fang Xiang]

In non-coherent GIC design, ITS tables should be clean and flushed
to the PoV of the ITS before writing GITS_BASER<n> registers, otherwise
the ITS would read dirty tables and lead to UNPREDICTABLE behaviors.

The ITS always got clean tables in initialization with this fix, by
observing the signals from GIC.

Furthermore, hoist the quirked non-shareable attributes earlier to
save effort in tables setup.

Suggested-by: Marc Zyngier <maz at kernel.org>
Signed-off-by: Fang Xiang <fangxiang3 at xiaomi.com>
Tested-by: Fang Xiang <fangxiang3 at xiaomi.com>
---
Link to v3:
https://lore.kernel.org/all/20231030070020.3689-1-fangxiang3@xiaomi.com/

Link to v2:
https://lore.kernel.org/all/20231027031007.2088-1-fangxiang3@xiaomi.com/

Link to v1:
https://lore.kernel.org/all/20231026020116.4238-1-fangxiang3@xiaomi.com/

v3-> v4:
    - Change 'Signed-off-by' trailer to 'Suggested-by' for original
      author Marc
    - Fix the format of commit message

v2 -> v3:
    - Add 'Signed-off-by' trailer for original author Marc
    - Expand commit message with testing result

v1 -> v2:
    - Flush ITS tables before writing GITS_BASER<n> registers
    - Hoist the quirked non-shareable attributes earlier
---
 drivers/irqchip/irq-gic-v3-its.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c
index 75a2dd550625..d76d44ea2de1 100644
--- a/drivers/irqchip/irq-gic-v3-its.c
+++ b/drivers/irqchip/irq-gic-v3-its.c
@@ -2379,12 +2379,12 @@ static int its_setup_baser(struct its_node *its, struct its_baser *baser,
 		break;
 	}
 
+	if (!shr)
+		gic_flush_dcache_to_poc(base, PAGE_ORDER_TO_SIZE(order));
+
 	its_write_baser(its, baser, val);
 	tmp = baser->val;
 
-	if (its->flags & ITS_FLAGS_FORCE_NON_SHAREABLE)
-		tmp &= ~GITS_BASER_SHAREABILITY_MASK;
-
 	if ((val ^ tmp) & GITS_BASER_SHAREABILITY_MASK) {
 		/*
 		 * Shareability didn't stick. Just use
@@ -2394,10 +2394,9 @@ static int its_setup_baser(struct its_node *its, struct its_baser *baser,
 		 * non-cacheable as well.
 		 */
 		shr = tmp & GITS_BASER_SHAREABILITY_MASK;
-		if (!shr) {
+		if (!shr)
 			cache = GITS_BASER_nC;
-			gic_flush_dcache_to_poc(base, PAGE_ORDER_TO_SIZE(order));
-		}
+
 		goto retry_baser;
 	}
 
@@ -2609,6 +2608,11 @@ static int its_alloc_tables(struct its_node *its)
 		/* erratum 24313: ignore memory access type */
 		cache = GITS_BASER_nCnB;
 
+	if (its->flags & ITS_FLAGS_FORCE_NON_SHAREABLE) {
+		cache = GITS_BASER_nC;
+		shr = 0;
+	}
+
 	for (i = 0; i < GITS_BASER_NR_REGS; i++) {
 		struct its_baser *baser = its->tables + i;
 		u64 val = its_read_baser(its, baser);
-- 
2.34.1