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charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: iommu-bounces@lists.linux-foundation.org Sender: "iommu" 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 > > > 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. > > [1] https://patchwork.kernel.org/comment/23149049/ > [2] https://patchwork.kernel.org/cover/11279577/ 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. -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTC broadband for 0.8mile line in suburbia: sync at 12.1Mbps down 622kbps up According to speedtest.net: 11.9Mbps down 500kbps up _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu