linux-kernel - [PATCH 1/4] of: also handle dma-noncoherent in of_dma_is

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Date:   Sun, 19 Jun 2022 22:32:09 +0200
From:   Heiko Stuebner <heiko@...ech.de>
To:     palmer@...belt.com, paul.walmsley@...ive.com
Cc:     linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        wefu@...hat.com, guoren@...nel.org, cmuellner@...ux.com,
        philipp.tomsich@...ll.eu, hch@....de, samuel@...lland.org,
        atishp@...shpatra.org, anup@...infault.org, mick@....forth.gr,
        robh+dt@...nel.org, krzk+dt@...nel.org, devicetree@...r.kernel.org,
        drew@...gleboard.org, rdunlap@...radead.org,
        Heiko Stuebner <heiko@...ech.de>
Subject: [PATCH 1/4] of: also handle dma-noncoherent in of_dma_is_coherent()

of_dma_is_coherent() currently expects the architecture to be
non-coherent and some devices being coherent getting marked
as such with the dma-coherent devicetree property.

For PowerPC CONFIG_OF_DMA_DEFAULT_COHERENT was added which currently
makes of_dma_is_coherent() always return true but doesn't handle
the case of the architecture being coherent but some devices not.

So modify the function to also check for dma-noncoherent and
set a suitable default return value. If CONFIG_OF_DMA_DEFAULT_COHERENT
is set the value starts with true and finding dma-noncoherent will
set it to false and without CONFIG_OF_DMA_DEFAULT_COHERENT, the
behaviour is reversed.

Signed-off-by: Heiko Stuebner <heiko@...ech.de>
---
 drivers/of/address.c | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/drivers/of/address.c b/drivers/of/address.c
index 94f017d808c4..1c362d09983d 100644
--- a/drivers/of/address.c
+++ b/drivers/of/address.c
@@ -1045,26 +1045,32 @@ phys_addr_t __init of_dma_get_max_cpu_address(struct device_node *np)
  *
  * It returns true if "dma-coherent" property was found
  * for this device in the DT, or if DMA is coherent by
- * default for OF devices on the current platform.
+ * default for OF devices on the current platform and no
+ * "dma-noncoherent" property was found for this device.
  */
 bool of_dma_is_coherent(struct device_node *np)
 {
 	struct device_node *node;
+	bool ret = false;
 
 	if (IS_ENABLED(CONFIG_OF_DMA_DEFAULT_COHERENT))
-		return true;
+		ret = true;
 
 	node = of_node_get(np);
 
 	while (node) {
 		if (of_property_read_bool(node, "dma-coherent")) {
-			of_node_put(node);
-			return true;
+			ret = true;
+			break;
+		}
+		if (of_property_read_bool(node, "dma-noncoherent")) {
+			ret = false;
+			break;
 		}
 		node = of_get_next_dma_parent(node);
 	}
 	of_node_put(node);
-	return false;
+	return ret;
 }
 EXPORT_SYMBOL_GPL(of_dma_is_coherent);
 
-- 
2.35.1