From: gregory.clement@free-electrons•com (Gregory CLEMENT)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCHv2 2/3] ARM: mvebu: disable I/O coherency on non-SMP situations on Armada 370/XP
Date: Fri, 31 Oct 2014 14:46:58 +0100 [thread overview]
Message-ID: <545392D2.8050202@free-electrons.com> (raw)
In-Reply-To: <1414423955-5933-3-git-send-email-thomas.petazzoni@free-electrons.com>
Hi Thomas,
I agree that providing a kernel working reliably is important.
On 27/10/2014 16:32, Thomas Petazzoni wrote:
> 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@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>
Thanks,
Gregory
--
Gregory Clement, Free Electrons
Kernel, drivers, real-time and embedded Linux
development, consulting, training and support.
http://free-electrons.com
next prev parent reply other threads:[~2014-10-31 13:46 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-10-27 15:32 [PATCHv2 0/3] ARM: mvebu: disable I/O coherency on !SMP Thomas Petazzoni
2014-10-27 15:32 ` [PATCHv2 1/3] ARM: mvebu: make the coherency_ll.S functions work with no coherency fabric Thomas Petazzoni
2014-10-31 13:39 ` Gregory CLEMENT
2014-10-27 15:32 ` [PATCHv2 2/3] ARM: mvebu: disable I/O coherency on non-SMP situations on Armada 370/XP Thomas Petazzoni
2014-10-31 13:46 ` Gregory CLEMENT [this message]
2014-11-07 2:53 ` Jason Cooper
2014-10-27 15:32 ` [PATCHv2 3/3] ARM: mvebu: add missing of_node_put() call in coherency.c Thomas Petazzoni
2014-10-31 13:49 ` Gregory CLEMENT
2014-11-07 2:57 ` Jason Cooper
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