On 04.03.2020 12:52, Russell King - ARM Linux admin wrote:
On Wed, Mar 04, 2020 at 12:33:14PM +0200, Laurentiu Tudor wrote:
On 04.03.2020 12:07, Russell King - ARM Linux admin wrote:
On Wed, Mar 04, 2020 at 11:56:53AM +0200, Laurentiu Tudor wrote:
From 44ae46501b5379bd0890df87fd3827248626ed03 Mon Sep 17 00:00:00 2001
From: Laurentiu Tudor <[email protected]>
Date: Tue, 1 Oct 2019 16:22:48 +0300
Subject: [PATCH 1/6] bus: fsl-mc: make mc work with smmu disable bypass on
Content-Type: text/plain; charset="us-ascii"
Since this commit [1] booting kernel on MC based chips started to
fail because this firmware starts before the kernel and as soon as
SMMU is probed it starts to trigger contiguous faults.
I think you mean "continuous" here.
Yes, thanks.
This is a workaround that allows MC firmware to run with SMMU
in disable bypass mode. It consists of the following steps:
1. pause the firmware at early boot to get a chance to setup SMMU
2. request direct mapping for MC device
3. resume the firmware
The workaround relies on the fact that no state is lost when
pausing / resuming firmware, as per the docs.
With this patch, platforms with MC firmware can now boot without
having to change the default config to set:
CONFIG_ARM_SMMU_DISABLE_BYPASS_BY_DEFAULT=n
This alone is a definite improvement, and has been needed for a while.
Please submit this patch with an appropriate Fixes: tag so stable trees
can pick it up.
The thing is that probably this workaround will never make it in the kernel
because it questionable to say the least, e.g. see [1]. My plan is to give
this approach [2] a try sometime soon.
So, if we want to reduce the iommu noise, we need to completely break
the ability to use a mainline kernel on the LX2160A. This doesn't
seem practical nor sensible. Someone has to give.
Well, I think it's a bit too early for such conclusions. I'd consider
this stuff early / experimental work, probably will take quite a while
for the dust to settle. Anyway, I'll take care not to break the kernel
when I'll start submitting more official patches.
For now, I'm just hoping that this stuff helps fixing your local tree.
---
Best Regards, Laurentiu
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