Re: [PATCH v4] devicetree: Add generic IOMMU device tree bindings

[Thierry Reding <thierry.reding@gmail.com>]

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On Thu, Jul 31, 2014 at 12:23:51PM +0200, Joerg Roedel wrote:
> On Thu, Jul 31, 2014 at 12:18:08PM +0200, Thierry Reding wrote:
> > It looks like this hasn't been applied yet, so I can send out a v5
> > shortly with the requested changes addressed.
> 
> Yes, please send a v5 with the requested changes and all Reviewed-bys
> and Acked-bys this got so far. I'll take it into my tree then if nobody
> else objects.

I just sent out v5, although I trimmed the Cc list a little since it was
growing somewhat long. But I've kept everyone that gave feedback on v4
as well as the lists.

For reference I've attached the diff since v4.

Thierry

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diff --git a/Documentation/devicetree/bindings/iommu/iommu.txt b/Documentation/devicetree/bindings/iommu/iommu.txt
index 464a81eaaf61..5a8b4624defc 100644
--- a/Documentation/devicetree/bindings/iommu/iommu.txt
+++ b/Documentation/devicetree/bindings/iommu/iommu.txt
@@ -82,7 +82,9 @@ device's parent node it will be ignored. An exception to this rule is if the
 referenced IOMMU is disabled, in which case the "dma-ranges" property of the
 parent shall take effect. Note that merely disabling a device tree node does
 not guarantee that the IOMMU is really disabled since the hardware may not
-have a means to turn off translation.
+have a means to turn off translation. But it is invalid in such cases to
+disable the IOMMU's device tree node in the first place because it would
+prevent any driver from properly setting up the translations.
 
 
 Notes:
@@ -108,7 +110,7 @@ Single-master IOMMU:
 	};
 
 	master {
-		iommus = <&/iommu>;
+		iommus = <&{/iommu}>;
 	};
 
 Multiple-master IOMMU with fixed associations:
@@ -117,8 +119,12 @@ Multiple-master IOMMU with fixed associations:
 	/* multiple-master IOMMU */
 	iommu {
 		/*
-		 * Masters are statically associated with this IOMMU and
-		 * address translation is always enabled.
+		 * Masters are statically associated with this IOMMU and share
+		 * the same address translations because the IOMMU does not
+		 * have sufficient information to distinguish between masters.
+		 *
+		 * Consequently address translation is always on or off for
+		 * all masters at any given point in time.
 		 */
 		#iommu-cells = <0>;
 	};
@@ -126,13 +132,13 @@ Multiple-master IOMMU with fixed associations:
 	/* static association with IOMMU */
 	master@1 {
 		reg = <1>;
-		iommus = <&/iommu>;
+		iommus = <&{/iommu}>;
 	};
 
 	/* static association with IOMMU */
 	master@2 {
 		reg = <2>;
-		iommus = <&/iommu>;
+		iommus = <&{/iommu}>;
 	};
 
 Multiple-master IOMMU:
@@ -145,28 +151,32 @@ Multiple-master IOMMU:
 
 	master@1 {
 		/* device has master ID 42 in the IOMMU */
-		iommus = <&/iommu 42>;
+		iommus = <&{/iommu} 42>;
 	};
 
 	master@2 {
 		/* device has master IDs 23 and 24 in the IOMMU */
-		iommus = <&/iommu 23>, <&/iommu 24>;
+		iommus = <&{/iommu} 23>, <&{/iommu} 24>;
 	};
 
 Multiple-master IOMMU with configurable DMA window:
 ---------------------------------------------------
 
 	/ {
-		#address-cells = <1>;
-		#size-cells = <1>;
-
 		iommu {
-			/* master ID, address and length of DMA window */
+			/*
+			 * One cell for the master ID and one cell for the
+			 * address of the DMA window. The length of the DMA
+			 * window is encoded in two cells.
+			 *
+			 * The DMA window is the range addressable by the
+			 * master (i.e. the I/O virtual address space).
+			 */
 			#iommu-cells = <4>;
 		};
 
 		master {
 			/* master ID 42, 4 GiB DMA window starting at 0 */
-			iommus = <&/iommu  42  0  0x1 0x0>;
+			iommus = <&{/iommu}  42  0  0x1 0x0>;
 		};
 	};

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