iommu.lists.linux-foundation.org archive mirror
 help / color / mirror / Atom feed
From: Mark Kettenis <mark.kettenis@xs4all.nl>
To: Arnd Bergmann <arnd@kernel.org>
Cc: robh@kernel.org, sven@svenpeter.dev, devicetree@vger.kernel.org,
	will@kernel.org, marcan@marcan.st, linux-kernel@vger.kernel.org,
	iommu@lists.linux-foundation.org, maz@kernel.org,
	mohamed.mediouni@caramail.com, robin.murphy@arm.com,
	linux-arm-kernel@lists.infradead.org, stan@corellium.com
Subject: Re: [PATCH 0/3] Apple M1 DART IOMMU driver
Date: Fri, 26 Mar 2021 22:16:14 +0100 (CET)	[thread overview]
Message-ID: <c1bcda7f8ba573bd@bloch.sibelius.xs4all.nl> (raw)
In-Reply-To: <CAK8P3a1+BOmT39k=OqFU+LtgfW=SDCp5W69YW58sVGf66mSppw@mail.gmail.com> (message from Arnd Bergmann on Fri, 26 Mar 2021 20:59:58 +0100)

> From: Arnd Bergmann <arnd@kernel.org>
> Date: Fri, 26 Mar 2021 20:59:58 +0100
> 
> On Fri, Mar 26, 2021 at 6:51 PM Sven Peter <sven@svenpeter.dev> wrote:
> > On Fri, Mar 26, 2021, at 18:34, Robin Murphy wrote:
> > > On 2021-03-26 17:26, Mark Kettenis wrote:
> > > >
> > > > Anyway, from my viewpoint having the information about the IOVA
> > > > address space sit on the devices makes little sense.  This information
> > > > is needed by the DART driver, and there is no direct cnnection from
> > > > the DART to the individual devices in the devicetree.  The "iommus"
> > > > property makes a connection in the opposite direction.
> > >
> > > What still seems unclear is whether these addressing limitations are a
> > > property of the DART input interface, the device output interface, or
> > > the interconnect between them. Although the observable end result
> > > appears more or less the same either way, they are conceptually
> > > different things which we have different abstractions to deal with.
> >
> > I'm not really sure if there is any way for us to figure out where these
> > limitation comes from though.
> 
> My first guess was that this is done to partition the available address
> address space in a way that allows one physical IOTLB to handle
> multiple devices that each have their own page table for a subset
> of the address space, as was done on old PowerPC IOMMUs.
> However, the ranges you list don't really support that model.
> 
> > I've done some more experiments and looked at all DART nodes in Apple's Device
> > Tree though. It seems that most (if not all) masters only connect 32 address
> > lines even though the iommu can handle a much larger address space. I'll therefore
> > remove the code to handle the full space for v2 since it's essentially dead
> > code that can't be tested anyway.
> >
> >
> > There are some exceptions though:
> >
> > There are the PCIe DARTs which have a different limitation which could be
> > encoded as 'dma-ranges' in the pci bus node:
> >
> >            name         base      size
> >          dart-apcie1: 00100000  3fe00000
> >          dart-apcie2: 00100000  3fe00000
> >          dart-apcie0: 00100000  3fe00000
> >         dart-apciec0: 00004000  7fffc000
> >         dart-apciec1: 80000000  7fffc000
> 
> This looks like they are reserving some address space in the beginning
> and/or the end, and for apciec0, the address space is partitioned into
> two equal-sized regions.
> 
> > Then there are also these display controller DARTs. If we wanted to use dma-ranges
> > we could just put them in a single sub bus:
> >
> >               name     base      size
> >           dart-disp0: 00000000 fc000000
> >             dart-dcp: 00000000 fc000000
> >        dart-dispext0: 00000000 fc000000
> >          dart-dcpext: 00000000 fc000000
> >
> >
> > And finally we have these strange ones which might eventually each require
> > another awkward sub-bus if we want to stick to the dma-ranges property.
> >
> >     name     base      size
> >   dart-aop: 00030000 ffffffff ("always-on processor")
> >   dart-pmp: 00000000 bff00000 (no idea yet)
> 
> Here I also see a "pio-vm-size" property:
> 
>     dart-pmp {
>       pio-vm-base = <0xc0000000>;
>       pio-vm-size = <0x40000000>;
>       vm-size = <0xbff00000>;
>       ...
>    };
> 
> Which seems to give 3GB of address space to the normal iotlb,
> plus the last 1GB to something else. The vm-base property is also
> missing rather than zero, but that could just be part of their syntax
> instead of a real difference.

Yes.  It seems like "vm-base" is omitted when it is 0, and "vm-size"
is omitted when the end of the window is at 0xffffffff.

> 
> Could it be that there are
> 
> >   dart-sio: 0021c000 fbde4000 (at least their Secure Enclave/TPM co-processor)
> 
> Same here:
>     dart-sio {
>        vm-base = <0x0>;
>        vm-size = <0xfc000000>;
>        pio-vm-base = <0xfd000000>;
>       pio-vm-size = <0x2000000>;
>       pio-granularity = <0x1000000>;
>    }
> 
> There are clearly two distinct ranges that split up the 4GB space again,
> with a small hole of 16MB (==pio-granularity) at the end of each range.
> 
> The "pio" name might indicate that this is a range of addresses that
> can be programmed to point at I/O registers in another device, rather
> than pointing to RAM.
> 
>            Arnd
> 
_______________________________________________
iommu mailing list
iommu@lists.linux-foundation.org
https://lists.linuxfoundation.org/mailman/listinfo/iommu

  reply	other threads:[~2021-03-26 21:16 UTC|newest]

Thread overview: 36+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-20 15:19 Sven Peter via iommu
2021-03-20 15:19 ` [PATCH 1/3] iommu: io-pgtable: add DART pagetable format Sven Peter via iommu
2021-03-24 16:37   ` Robin Murphy
2021-03-25 20:47     ` Sven Peter via iommu
2021-03-20 15:20 ` [PATCH 2/3] dt-bindings: iommu: add DART iommu bindings Sven Peter via iommu
2021-03-22  0:15   ` Rob Herring
2021-03-22 18:16     ` Sven Peter via iommu
2021-03-21 16:00 ` [PATCH 0/3] Apple M1 DART IOMMU driver Mark Kettenis
2021-03-21 17:22   ` Sven Peter via iommu
2021-03-21 18:35     ` Mark Kettenis
2021-03-22 22:17       ` Sven Peter via iommu
2021-03-23 20:00         ` Mark Kettenis
2021-03-23 21:03           ` Sven Peter via iommu
2021-03-21 17:28   ` Sven Peter via iommu
2021-03-23 20:53   ` Rob Herring
2021-03-23 22:33     ` Mark Kettenis
2021-03-25  7:53     ` Sven Peter via iommu
2021-03-25 11:50       ` Robin Murphy
2021-03-25 20:49         ` Sven Peter via iommu
2021-03-27 15:33         ` Sven Peter via iommu
2021-03-25 21:41       ` Arnd Bergmann
2021-03-26 15:59         ` Mark Kettenis
2021-03-26 16:09           ` Arnd Bergmann
2021-03-26 16:10           ` Sven Peter via iommu
2021-03-26 16:38             ` Arnd Bergmann
2021-03-26 17:06               ` Sven Peter via iommu
2021-03-26 17:26               ` Mark Kettenis
2021-03-26 17:34                 ` Robin Murphy
2021-03-26 17:51                   ` Sven Peter via iommu
2021-03-26 19:59                     ` Arnd Bergmann
2021-03-26 21:16                       ` Mark Kettenis [this message]
2021-03-27 15:30                       ` Sven Peter via iommu
2021-03-26 20:03                 ` Arnd Bergmann
2021-03-26 21:13                   ` Mark Kettenis
2021-03-24 15:29 ` Robin Murphy
2021-03-25  7:58   ` Sven Peter via iommu

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=c1bcda7f8ba573bd@bloch.sibelius.xs4all.nl \
    --to=mark.kettenis@xs4all.nl \
    --cc=arnd@kernel.org \
    --cc=devicetree@vger.kernel.org \
    --cc=iommu@lists.linux-foundation.org \
    --cc=linux-arm-kernel@lists.infradead.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=marcan@marcan.st \
    --cc=maz@kernel.org \
    --cc=mohamed.mediouni@caramail.com \
    --cc=robh@kernel.org \
    --cc=robin.murphy@arm.com \
    --cc=stan@corellium.com \
    --cc=sven@svenpeter.dev \
    --cc=will@kernel.org \
    --subject='Re: [PATCH 0/3] Apple M1 DART IOMMU driver' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).