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author | Thomas Petazzoni <thomas.petazzoni@free-electrons.com> | 2014-11-13 10:38:57 +0100 |
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committer | Jason Cooper <jason@lakedaemon.net> | 2014-11-22 02:49:33 +0100 |
commit | e55355453600a33bb5ca4f71f2d7214875f3b061 (patch) | |
tree | 6155d933799315d876054ab5db481c1577807fc4 /arch/arm/mach-mvebu | |
parent | ARM: mvebu: make the coherency_ll.S functions work with no coherency fabric (diff) | |
download | linux-e55355453600a33bb5ca4f71f2d7214875f3b061.tar.xz linux-e55355453600a33bb5ca4f71f2d7214875f3b061.zip |
ARM: mvebu: disable I/O coherency on non-SMP situations on Armada 370/375/38x/XP
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@free-electrons.com>
Fixes: e60304f8cb7bb545e79fe62d9b9762460c254ec2 ("arm: mvebu: Add hardware I/O Coherency support")
Cc: <stable@vger.kernel.org> # v3.8+
Acked-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
Link: https://lkml.kernel.org/r/1415871540-20302-3-git-send-email-thomas.petazzoni@free-electrons.com
Signed-off-by: Jason Cooper <jason@lakedaemon.net>
Diffstat (limited to 'arch/arm/mach-mvebu')
-rw-r--r-- | arch/arm/mach-mvebu/coherency.c | 44 |
1 files 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) |