From: will.deacon@arm•com (Will Deacon)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH v3 3/6] iommu: add ARM short descriptor page table allocator.
Date: Tue, 28 Jul 2015 14:47:10 +0100 [thread overview]
Message-ID: <20150728134710.GM29209@arm.com> (raw)
In-Reply-To: <1438090663.25925.75.camel@mhfsdcap03>
On Tue, Jul 28, 2015 at 02:37:43PM +0100, Yong Wu wrote:
> On Tue, 2015-07-28 at 12:00 +0100, Will Deacon wrote:
> > On Tue, Jul 28, 2015 at 06:08:14AM +0100, Yong Wu wrote:
> > > On Mon, 2015-07-27 at 15:11 +0100, Will Deacon wrote:
> > > > On Mon, Jul 27, 2015 at 03:05:38PM +0100, Robin Murphy wrote:
> > > > > On 27/07/15 05:21, Yong Wu wrote:
> > > > > >>>>> + } else { /* page or largepage */
> > > > > >>>>> + if (quirk & IO_PGTABLE_QUIRK_SHORT_MTK) {
> > > > > >>>>> + if (large) { /* special Bit */
> > > > > >>>>
> > > > > >>>> This definitely needs a better comment! What exactly are you doing here
> > > > > >>>> and what is that quirk all about?
> > > > > >>>
> > > > > >>> I use this quirk is for MTK Special Bit as we don't have the XN bit in
> > > > > >>> pagetable.
> > > > > >>
> > > > > >> I'm still not really clear about what this is.
> > > > > >
> > > > > > There is some difference between the standard spec and MTK HW,
> > > > > > Our hw don't implement some bits, like XN and AP.
> > > > > > So I add a quirk for MTK special.
> > > > >
> > > > > When you say it doesn't implement these bits, do you mean that having
> > > > > them set will lead to Bad Things happening in the hardware, or that it
> > > > > will simply ignore them and not enforce any of the protections they
> > > > > imply? The former case would definitely want clearly documenting
> > > > > somewhere, whereas for the latter case I'm not sure it's even worth the
> > > > > complication of having a quirk - if the value doesn't matter there seems
> > > > > little point in doing a special dance just for the sake of semantic
> > > > > correctness of the in-memory PTEs, in my opinion.
> > > >
> > > > Agreed. We should only use quirks if the current (architecturally
> > > > compliant) code causes real issues with the hardware. Then the quirk can
> > > > be used to either avoid the problematic routines or to take extra steps
> > > > to make things work as the architecture intended.
> > > >
> > > > I've asked how this IOMMU differs from the architecture on a number of
> > > > occasions, but I'm still yet to receive a response other than "it's special".
> > > >
> > >
> > > After check further with DE, Our pagetable is refer to ARM-v7's
> > > short-descriptor which is a little different from ARM-v8. like bit0(PXN)
> > > in section and supersection, I didn't read ARM-v7 spec before, so I add
> > > a MTK quirk to disable PXN bit in section and supersection.(if the PXN
> > > bit is wrote in ARM-v7 spec, HW will page fault.)
> >
> > I've been reviewing this using the ARMv7 ARM (Rev.C of DDI0406C) the whole
> > time. PXN is there as an optional field in non-LPAE implementations. That's
> > fine and doesn't require any quirks.
>
> Thanks for your confirm.
> Then I delete all the PXN bit in here?
>
> Take a example,
> #define ARM_SHORT_PGD_SECTION_XN (BIT(0) | BIT(4))
> I will change it to "BIT(4)".
Yes. Then the PXN bit can be added later as a quirk when we have an
implementation that supports it.
Will
next prev parent reply other threads:[~2015-07-28 13:47 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-07-16 9:04 [PATCH v3 0/6] MT8173 IOMMU SUPPORT Yong Wu
2015-07-16 9:04 ` [PATCH v3 1/6] dt-bindings: iommu: Add binding for mediatek IOMMU Yong Wu
2015-07-16 9:04 ` [PATCH v3 2/6] dt-bindings: mediatek: Add smi dts binding Yong Wu
2015-07-16 9:04 ` [PATCH v3 3/6] iommu: add ARM short descriptor page table allocator Yong Wu
2015-07-21 17:11 ` Will Deacon
2015-07-24 5:24 ` Yong Wu
2015-07-24 16:53 ` Will Deacon
2015-07-27 4:21 ` Yong Wu
2015-07-27 14:05 ` Robin Murphy
2015-07-27 14:11 ` Will Deacon
2015-07-28 5:08 ` Yong Wu
2015-07-28 11:00 ` Will Deacon
2015-07-28 13:37 ` Yong Wu
2015-07-28 13:47 ` Will Deacon [this message]
[not found] ` <1438329337.25925.147.camel@mhfsdcap03>
2015-07-31 11:32 ` Will Deacon
2015-09-14 12:25 ` Yong Wu
2015-09-16 12:55 ` Will Deacon
2015-09-17 2:38 ` Yong Wu
2015-07-16 9:04 ` [PATCH v3 4/6] memory: mediatek: Add SMI driver Yong Wu
2015-07-16 9:04 ` [PATCH v3 5/6] iommu/mediatek: Add mt8173 IOMMU driver Yong Wu
2015-07-21 14:59 ` Will Deacon
2015-07-24 5:43 ` Yong Wu
2015-07-24 16:55 ` Will Deacon
2015-07-27 4:24 ` Yong Wu
2015-07-27 15:48 ` Will Deacon
2015-07-27 13:23 ` Robin Murphy
2015-07-27 15:31 ` Russell King - ARM Linux
2015-07-27 15:49 ` Robin Murphy
2015-07-29 5:41 ` Yong Wu
2015-07-29 10:31 ` Will Deacon
2015-07-29 6:32 ` Yong Wu
2015-07-16 9:04 ` [PATCH v3 6/6] dts: mt8173: Add iommu/smi nodes for mt8173 Yong Wu
2015-07-23 14:40 ` Daniel Kurtz
2015-07-29 7:29 ` Yong Wu
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