3.16.7-ckt4 -stable review patch. If anyone has any objections, please let me know.
------------------
From: Thomas Petazzoni <thomas.petazzoni@xxxxxxxxxxxxxxxxxx>
commit e55355453600a33bb5ca4f71f2d7214875f3b061 upstream.
Enabling the hardware I/O coherency on Armada 370, Armada 375, Armada
38x and Armada XP requires a certain number of conditions:
- On Armada 370, the cache policy must be set to write-allocate.
- On Armada 375, 38x and 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")
Acked-by: Gregory CLEMENT <gregory.clement@xxxxxxxxxxxxxxxxxx>
Link: https://lkml.kernel.org/r/1415871540-20302-3-git-send-email-thomas.petazzoni@xxxxxxxxxxxxxxxxxx
Signed-off-by: Jason Cooper <jason@xxxxxxxxxxxxxx>
Signed-off-by: Luis Henriques <luis.henriques@xxxxxxxxxxxxx>
---
arch/arm/mach-mvebu/coherency.c | 44 ++++++++++++++++++++++++++++-------------
1 file changed, 30 insertions(+), 14 deletions(-)
diff --git a/arch/arm/mach-mvebu/coherency.c b/arch/arm/mach-mvebu/coherency.c
index 044b51185fcc..c31f4c00b1fc 100644
--- a/arch/arm/mach-mvebu/coherency.c
+++ b/arch/arm/mach-mvebu/coherency.c
@@ -361,25 +361,41 @@ 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. To lift this
+ * limitation, we would have to find a way to make the cache
+ * policy set to write-allocate (on all Armada SoCs), and to
+ * set the shareable attribute in page tables (on all Armada
+ * SoCs except the Armada 370). Unfortunately, such decisions
+ * are taken very early in the kernel boot process, at a point
+ * where we don't know yet on which SoC we are running.
- /* Armada 370/XP coherency works in both UP and SMP */
- if (type == COHERENCY_FABRIC_TYPE_ARMADA_370_XP)
- return type;
+ */
+ if (!is_smp())
+ return COHERENCY_FABRIC_TYPE_NONE;
- /* Armada 375 coherency works only on SMP */
- else if (type == COHERENCY_FABRIC_TYPE_ARMADA_375 && is_smp())
- return type;
+ np = of_find_matching_node_and_match(NULL, of_coherency_table, &match);
+ if (!np)
+ return COHERENCY_FABRIC_TYPE_NONE;
- /* Armada 380 coherency works only on SMP */
- else if (type == COHERENCY_FABRIC_TYPE_ARMADA_380 && is_smp())
- return type;
- }
+ type = (int) match->data;
+
+ of_node_put(np);
- return COHERENCY_FABRIC_TYPE_NONE;
+ return type;
}
int coherency_available(void)
--
2.1.4
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