Enabling the hardware I/O coherency on Armada 370 and Armada XP
requires a certain number of conditions:
- On Armada 370, the cache policy must be set to write-allocate.
- On Armada XP, the cache policy must be set to write-allocate, the
pages must be mapped with the shareable attribute, and the SMP bit
must be set
Currently, on Armada XP, when CONFIG_SMP is enabled, those conditions
are met. However, when Armada XP is used in a !CONFIG_SMP kernel, none
of these conditions are met. With Armada 370, the situation is worse:
since the processor is single core, regardless of whether CONFIG_SMP
or !CONFIG_SMP is used, the cache policy will be set to write-back by
the kernel and not write-allocate.
Since solving this problem turns out to be quite complicated, and we
don't want to let users with a mainline kernel known to have
infrequent but existing data corruptions, this commit proposes to
simply disable hardware I/O coherency in situations where it is known
not to work.
And basically, the is_smp() function of the kernel tells us whether it
is OK to enable hardware I/O coherency or not, so this commit slightly
refactors the coherency_type() function to return
COHERENCY_FABRIC_TYPE_NONE when is_smp() is false, or the appropriate
type of the coherency fabric in the other case.
Thanks to this, the I/O coherency fabric will no longer be used at all
in !CONFIG_SMP configurations. It will continue to be used in
CONFIG_SMP configurations on Armada XP, Armada 375 and Armada 38x
(which are multiple cores processors), but will no longer be used on
Armada 370 (which is a single core processor).
In the process, it simplifies the implementation of the
coherency_type() function, and adds a missing call to of_node_put().
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@xxxxxxxxxxxxxxxxxx>
Fixes: e60304f8cb7bb545e79fe62d9b9762460c254ec2 ("arm: mvebu: Add hardware I/O Coherency support")
Cc: <stable@xxxxxxxxxxxxxxx> # v3.8+
---
arch/arm/mach-mvebu/coherency.c | 37 +++++++++++++++++++++++--------------
1 file changed, 23 insertions(+), 14 deletions(-)
diff --git a/arch/arm/mach-mvebu/coherency.c b/arch/arm/mach-mvebu/coherency.c
index 2bdc323..abf4535 100644
--- a/arch/arm/mach-mvebu/coherency.c
+++ b/arch/arm/mach-mvebu/coherency.c
@@ -361,25 +361,34 @@ static int coherency_type(void)
{
struct device_node *np;
const struct of_device_id *match;
+ int type;
- np = of_find_matching_node_and_match(NULL, of_coherency_table, &match);
- if (np) {
- int type = (int) match->data;
+ /*
+ * The coherency fabric is needed:
+ * - For coherency between processors on Armada XP, so only
+ * when SMP is enabled.
+ * - For coherency between the processor and I/O devices, but
+ * this coherency requires many pre-requisites (write
+ * allocate cache policy, shareable pages, SMP bit set) that
+ * are only meant in SMP situations.
+ *
+ * Note that this means that on Armada 370, there is currently
+ * no way to use hardware I/O coherency, because even when
+ * CONFIG_SMP is enabled, is_smp() returns false due to the
+ * Armada 370 being a single-core processor.
+ */
+ if (!is_smp())
+ return COHERENCY_FABRIC_TYPE_NONE;
- /* Armada 370/XP coherency works in both UP and SMP */
- if (type == COHERENCY_FABRIC_TYPE_ARMADA_370_XP)
- return type;
+ np = of_find_matching_node_and_match(NULL, of_coherency_table, &match);
+ if (!np)
+ return COHERENCY_FABRIC_TYPE_NONE;
- /* Armada 375 coherency works only on SMP */
- else if (type == COHERENCY_FABRIC_TYPE_ARMADA_375 && is_smp())
- return type;
+ type = (int) match->data;
- /* Armada 380 coherency works only on SMP */
- else if (type == COHERENCY_FABRIC_TYPE_ARMADA_380 && is_smp())
- return type;
- }
+ of_node_put(np);
- return COHERENCY_FABRIC_TYPE_NONE;
+ return type;
}
int coherency_available(void)
--
2.0.0
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