Hello Sasha! This backported mvebu fix seems to have slipped through the cracks by accident. IIUC, the OpenWRT mvebu maintainer(s) are particularily interested in having this bug fixed for 3.18-stable. See this thread for the original patch submission and discussion: http://permalink.gmane.org/gmane.linux.kernel.stable/127243 I'm including the full patch below for convenicence. It still applies to the current 3.18-stable tree (apply with "git am --scissors" if you use this email as source). I hope Thomas, Imre or Andrew can fill in the details if more background info is necessary... Thanks, Bjørn ---- >8 ---- >8 ---- From: Thomas Petazzoni <thomas.petazzoni@xxxxxxxxxxxxxxxxxx> Subject: ARM: mvebu: do not register custom DMA operations when coherency is disabled Date: Thu, 12 Mar 2015 11:58:12 +0100 This patch is a partial backport of commit ef01c6c36bb8 ("ARM: mvebu: remove Armada 375 Z1 workaround for I/O coherency"). This commit was merged in v3.19, so kernel versions later than v3.19 are not affected by the problem that this commit fixes. It does not make a lot of sense to backport this commit entirely, since it is mainly removing some no longer useful code. However, this commit is also making sure that the bus_register_notifier that register the custom DMA operations that should be used for HW I/O coherency does not get registered when said HW I/O coherency is not enabled. This is particularly critical since we have decided to disable HW I/O coherency completely in all kernels < 4.0, to be on the safe side, while experimenting a new implementation of the HW I/O coherency in >= 4.0. Without this commit, kernels earlier than 3.18 have the custom DMA operations normally used for HW I/O coherency registered (they don't do cache maintenance operations), while HW I/O coherency is disabled. It essentially causes every DMA transfer to transfer garbage. The issue fixed by this commit was introduced by 5ab5afd8ba83 ("ARM: mvebu: implement Armada 375 coherency workaround"), but it was not visible until now since it didn't cause any problem when HW I/O coherency is enabled. Signed-off-by: Thomas Petazzoni <thomas.petazzoni@xxxxxxxxxxxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> v3.16..v3.18 --- arch/arm/mach-mvebu/coherency.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/arch/arm/mach-mvebu/coherency.c b/arch/arm/mach-mvebu/coherency.c index 2ffccd4..01efe13 100644 --- a/arch/arm/mach-mvebu/coherency.c +++ b/arch/arm/mach-mvebu/coherency.c @@ -448,8 +448,9 @@ static int __init coherency_late_init(void) armada_375_coherency_init_wa(); } - bus_register_notifier(&platform_bus_type, - &mvebu_hwcc_nb); + if (coherency_available()) + bus_register_notifier(&platform_bus_type, + &mvebu_hwcc_nb); return 0; } -- 2.1.0 -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html