[PATCH 2/2] irqchip/gic-v3-its: Make "dma-noncoherent" preferred for RK358x errata

[Dragan Simic]

The preferred way to denote hardware with non-coherent DMA is to use the
"dma-noncoherent" DT property, [1] instead of relying on the compatibles. [2]
Alas, older versions of the Rockchip RK3588 and RK3588S SoC dts(i) files
failed to specify this DT property, which means that checking the compatibles
remains required for backward SoC dts(i) compatibility.

Let's have the Rockchip 3588001 hardware errata handled the preferred way,
with newer versions of the Rockchip RK3588, RK3588S and RK3582 SoC dts(i)
files that properly specify the "dma-noncoherent" DT properties at both the
GIC redistributor and the GIC ITS levels, while falling back to checking the
compatibles for backward RK3588 and RK3588S SoC dts(i) compatibility.

[1] Documentation/devicetree/bindings/interrupt-controller/arm,gic-v3.yaml
[2] https://lore.kernel.org/linux-rockchip/86msgoozqa.wl-maz@kernel.org/

Cc: Marc Zyngier <maz at kernel.org>
Cc: FUKAUMI Naoki <naoki at radxa.com>
Signed-off-by: Dragan Simic <dsimic at manjaro.org>
---
 drivers/irqchip/irq-gic-v3-its.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c
index fdec478ba5e7..982dcbb30f39 100644
--- a/drivers/irqchip/irq-gic-v3-its.c
+++ b/drivers/irqchip/irq-gic-v3-its.c
@@ -4747,6 +4747,18 @@ static bool __maybe_unused its_enable_rk3588001(void *data)
 {
 	struct its_node *its = data;
 
+	/*
+	 * The preferred way to denote hardware with non-coherent DMA is to use
+	 * the "dma-noncoherent" DT property, which the older RK3588 SoC dts(i)
+	 * files failed to specify, relying on the compatibles instead.
+	 *
+	 * Thus, check for the presence of "dma-noncoherent" DT property first,
+	 * to let the hardware quirk be handled the preferred way, and fall back
+	 * to checking the compatibles for backward dts(i) compatibility.
+	 */
+	if (!of_dma_is_coherent(to_of_node(its->fwnode_handle)))
+		return false;
+
 	if (!of_machine_is_compatible("rockchip,rk3588") &&
 	    !of_machine_is_compatible("rockchip,rk3588s"))
 		return false;