From e55355453600a33bb5ca4f71f2d7214875f3b061 Mon Sep 17 00:00:00 2001 From: Thomas Petazzoni Date: Thu, 13 Nov 2014 10:38:57 +0100 Subject: 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 Fixes: e60304f8cb7bb545e79fe62d9b9762460c254ec2 ("arm: mvebu: Add hardware I/O Coherency support") Cc: # v3.8+ Acked-by: Gregory CLEMENT Link: https://lkml.kernel.org/r/1415871540-20302-3-git-send-email-thomas.petazzoni@free-electrons.com Signed-off-by: Jason Cooper --- arch/arm/mach-mvebu/coherency.c | 44 ++++++++++++++++++++++++++++------------- 1 file changed, 30 insertions(+), 14 deletions(-) (limited to 'arch') 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) -- cgit v1.2.3