linux-kernel - Re: [RFC 04/10] memory: Add Tegra124 memory controller support

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Message-ID: <20140627081659.GA10794@ulmo>
Date:	Fri, 27 Jun 2014 10:17:00 +0200
From:	Thierry Reding <thierry.reding@...il.com>
To:	Joseph Lo <josephl@...dia.com>
Cc:	Rob Herring <robh+dt@...nel.org>, Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Stephen Warren <swarren@...dotorg.org>,
	Arnd Bergmann <arnd@...db.de>,
	Will Deacon <will.deacon@....com>,
	Joerg Roedel <joro@...tes.org>,
	Cho KyongHo <pullip.cho@...sung.com>,
	Grant Grundler <grundler@...omium.org>,
	Dave Martin <Dave.Martin@....com>,
	Marc Zyngier <marc.zyngier@....com>,
	Hiroshi Doyu <hdoyu@...dia.com>,
	Olav Haugan <ohaugan@...eaurora.org>,
	Paul Walmsley <pwalmsley@...dia.com>,
	Rhyland Klein <rklein@...dia.com>,
	Allen Martin <AMartin@...dia.com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC 04/10] memory: Add Tegra124 memory controller support

On Fri, Jun 27, 2014 at 03:41:20PM +0800, Joseph Lo wrote:
> Hi Thierry,
> 
> On 06/27/2014 04:49 AM, Thierry Reding wrote:
> [snip]
> >+
> >+#define MC_INTSTATUS 0x000
> >+#define  MC_INT_DECERR_MTS (1 << 16)
> >+#define  MC_INT_SECERR_SEC (1 << 13)
> >+#define  MC_INT_DECERR_VPR (1 << 12)
> >+#define  MC_INT_INVALID_APB_ASID_UPDATE (1 << 11)
> >+#define  MC_INT_INVALID_SMMU_PAGE (1 << 10)
> >+#define  MC_INT_ARBITRATION_EMEM (1 << 9)
> >+#define  MC_INT_SECURITY_VIOLATION (1 << 8)
> >+#define  MC_INT_DECERR_EMEM (1 << 6)
> >+#define MC_INTMASK 0x004
> >+#define MC_ERR_STATUS 0x08
> >+#define MC_ERR_ADR 0x0c
> >+
> [snip]
> >+
> >+#define SMMU_PDE_ATTR          (SMMU_PDE_READABLE | SMMU_PDE_WRITABLE | \
> >+                                SMMU_PDE_NONSECURE)
> >+#define SMMU_PTE_ATTR          (SMMU_PTE_READABLE | SMMU_PTE_WRITABLE | \
> >+                                SMMU_PTE_NONSECURE)
> >+
> >+#define SMMU_PDE_VACANT(n)     (((n) << 10) | SMMU_PDE_ATTR)
> >+#define SMMU_PTE_VACANT(n)     (((n) << 12) | SMMU_PTE_ATTR)
> 
> There is an ISR to catch the invalid SMMU translation. Do you want to modify
> the identity mapping with read/write attribute of the unused SMMU pages?

I'm not sure I understand what you mean by "identity mapping". None of
the public documentation seems to describe the exact layout of PDEs or
PTEs, so it's somewhat hard to tell what to set them to when pages are
unmapped.

> This can make sure we capture the invalid SMMU translation. And helps for
> driver to capture issues when using SMMU.

That certainly sounds like a useful thing to have. Like I said this is
an RFC and I'm not even sure if it's acceptable in the current form, so
I wanted to get feedback early on to avoid wasting effort on something
that turn out to be a wild-goose chase.

Thierry

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