ARM: mvebu: completely disable hardware I/O coherency

tpetazzoni · lunn · commit 8f1e8ee28660 · 2015-01-17T11:46:55.000-06:00
The current hardware I/O coherency is known to cause problems with DMA
coherent buffers, as it still requires explicit I/O synchronization
barriers, which is not compatible with the semantics expected by the
Linux DMA coherent buffers API.

So, in order to have enough time to validate a new solution based on
automatic I/O synchronization barriers, this commit disables hardware
I/O coherency entirely. Future patches will re-enable it.

Signed-off-by: Thomas Petazzoni &lt;thomas.petazzoni@free-electrons.com&gt;
Cc: &lt;stable@vger.kernel.org&gt; # v3.8+
Signed-off-by: Andrew Lunn &lt;andrew@lunn.ch&gt;
diff --git a/arch/arm/mach-mvebu/coherency.c b/arch/arm/mach-mvebu/coherency.c
@@ -246,9 +246,14 @@ static int coherency_type(void)
 	return type;
 }
 
+/*
+ * As a precaution, we currently completely disable hardware I/O
+ * coherency, until enough testing is done with automatic I/O
+ * synchronization barriers to validate that it is a proper solution.
+ */
 int coherency_available(void)
 {
-	return coherency_type() != COHERENCY_FABRIC_TYPE_NONE;
+	return false;
 }
 
 int __init coherency_init(void)

Original file line number	Diff line number	Diff line change
`@@ -246,9 +246,14 @@ static int coherency_type(void)`
`246`	`246`	`return type;`
`247`	`247`	`}`
`248`	`248`
	`249`	`+/*`
	`250`	`+ * As a precaution, we currently completely disable hardware I/O`
	`251`	`+ * coherency, until enough testing is done with automatic I/O`
	`252`	`+ * synchronization barriers to validate that it is a proper solution.`
	`253`	`+ */`
`249`	`254`	`int coherency_available(void)`
`250`	`255`	`{`
`251`		`- return coherency_type() != COHERENCY_FABRIC_TYPE_NONE;`
	`256`	`+ return false;`
`252`	`257`	`}`
`253`	`258`
`254`	`259`	`int __init coherency_init(void)`