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

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Date:   Mon, 11 Jul 2022 02:04:31 +0300
From:   Sam Protsenko <semen.protsenko@...aro.org>
To:     David Virag <virag.david003@...il.com>
Cc:     Marek Szyprowski <m.szyprowski@...sung.com>,
        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, 3 Jul 2022 at 13:47, David Virag <virag.david003@...il.com> wrote:
>
> 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.
>

I don't have any manuals for v7.2, so I can only assume. Yes, it looks
to me very much like those EMU registers are missing in your SysMMU
IP-core: I remember seeing some similar SError messages while trying
to access some incorrect MMIO addresses. Good news is that once this
patch series is fixed and accepted, you can *probably* base your work
on top of it (as I only validated it with EMU registers for now). I
mean you can add some real IP-core users of that IOMMU, like graphics
(DPU), audio, camera, etc. Not sure though if it would be enough to
just add some DTS nodes, or your SoC support has to be added to some
drivers first.

> Best regards,
> David