riscv: implement Zicbom-based CMO instructions + the t-head variant

This series is based on the alternatives changes done in my svpbmt
series and thus also depends on Atish's isa-extension parsing series.

It implements using the cache-management instructions from the  Zicbom-
extension to handle cache flush, etc actions on platforms needing them.

SoCs using cpu cores from T-Head like the Allwinne D1 implement a
different set of cache instructions. But while they are different,
instructions they provide the same functionality, so a variant can easly
hook into the existing alternatives mechanism on those.

[Palmer:  Some minor fixups, including a RISCV_ISA_ZICBOM dependency on
MMU that's probably not strictly necessary.  The Zicbom support will
trip up sparse for users that have new toolchains, I just sent a patch.]

Link: https://lore.kernel.org/all/20220706231536.2041855-1-heiko@sntech.de/
Link: https://lore.kernel.org/linux-sparse/20220811033138.20676-1-palmer@rivosinc.com/T/#u

* palmer/riscv-zicbom:
  riscv: implement cache-management errata for T-Head SoCs
  riscv: Add support for non-coherent devices using zicbom extension
  dt-bindings: riscv: document cbom-block-size
  of: also handle dma-noncoherent in of_dma_is_coherent()

1 files changed, 10 insertions, 7 deletions

diff --git a/drivers/of/address.c b/drivers/of/address.c
index 94f017d808c4..96f0a12e507c 100644
--- a/drivers/of/address.c
+++ b/drivers/of/address.c
@@ -1045,26 +1045,29 @@ 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;
-
-	if (IS_ENABLED(CONFIG_OF_DMA_DEFAULT_COHERENT))
-		return true;
+	bool is_coherent = IS_ENABLED(CONFIG_OF_DMA_DEFAULT_COHERENT);
 
 	node = of_node_get(np);
 
 	while (node) {
 		if (of_property_read_bool(node, "dma-coherent")) {
-			of_node_put(node);
-			return true;
+			is_coherent = true;
+			break;
+		}
+		if (of_property_read_bool(node, "dma-noncoherent")) {
+			is_coherent = false;
+			break;
 		}
 		node = of_get_next_dma_parent(node);
 	}
 	of_node_put(node);
-	return false;
+	return is_coherent;
 }
 EXPORT_SYMBOL_GPL(of_dma_is_coherent);