linux-kernel - Re: [PATCH 0/4] iommu/exynos: Add basic support for SysMMU v7

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Date:   Sun, 03 Jul 2022 14:47:20 +0200
From:   David Virag <virag.david003@...il.com>
To:     Sam Protsenko <semen.protsenko@...aro.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>
Cc:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Janghyuck Kim <janghyuck.kim@...sung.com>,
        Cho KyongHo <pullip.cho@...sung.com>,
        Daniel Mentz <danielmentz@...gle.com>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        iommu@...ts.linux-foundation.org, iommu@...ts.linux.dev,
        linux-arm-kernel@...ts.infradead.org,
        linux-samsung-soc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/4] iommu/exynos: Add basic support for SysMMU v7

On Sun, 2022-07-03 at 00:48 +0300, Sam Protsenko wrote:
[...]
> Hi Marek,
> 
> As I understand, you have some board with SysMMU v7, which is not VM
> capable (judging from the patches you shared earlier). Could you
> please somehow verify if this series works fine for you? For example,
> this testing driver [1] can be helpful.
> 
> Thanks!
> 
> [1]
> https://github.com/joe-skb7/linux/commit/bbadd46fa525fe1fef2ccbdfff81f7d29caf0506

Hi Sam,

Not Marek here, but I wanted to try this on my jackpotlte (Exynos
7885). The driver reports it's DPU sysmmu as version 7.2, and manually
reading the capabilities registers it looks like it has the 2nd
capability register but not the VM capability.

After applying your patches, adding your test driver (with SYSMMU_BASE
corrected to 7885 value), and adding the sysmmu to dt, I tried to cat
the test file that it creates in debugfs and I got an SError kernel
panic.

I tried tracing where the SError happens and it looks like it's this
line:
	/* Preload for emulation */
	iowrite32(rw | vpn, obj->reg_base + MMU_EMU_PRELOAD);

Trying to read the EMU registers using devmem results in a "Bus error".

Could these emulation registers be missing from my SysMMU? Do you have
any info on what version should have it? Or maybe some capability bit?
I'll try testing it with DECON/DPP later and see if it works that way.

Best regards,
David