From: Andreas Herrmann <andreas.herrmann@calxeda.com>
To: Will Deacon <will.deacon@arm.com>
Cc: Olav Haugan <ohaugan@codeaurora.org>,
"devicetree-discuss@lists.ozlabs.org"
<devicetree-discuss@lists.ozlabs.org>,
"iommu@lists.linux-foundation.org"
<iommu@lists.linux-foundation.org>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH v2] documentation: iommu: add description of ARM System MMU binding
Date: Fri, 17 May 2013 22:16:39 +0200 [thread overview]
Message-ID: <20130517201639.GL10369@alberich> (raw)
In-Reply-To: <20130513104147.GF10369@alberich>
On Mon, May 13, 2013 at 12:41:47PM +0200, Andreas Herrmann wrote:
> On Mon, May 13, 2013 at 05:58:46AM -0400, Will Deacon wrote:
> > On Mon, May 13, 2013 at 10:50:20AM +0100, Andreas Herrmann wrote:
[snip]
> > > I also think that it is more useful to move the stream-id property to
> > > the device node of a master device. (It's a characteristic of the
> > > master device not of the SMMU.) Currently with multiple stream IDs per
> > > master device you have repeated entries in the mmu-master property.
> >
> > The problem with that approach is how to handle StreamID remastering. This
> > can and will happen, so the StreamID for a device is actually a property of
> > both the device *and* a particular point in the bus topology. Putting this
> > information in the device nodes will drag topology information all over the
> > place and I don't think it will make things clearer to read or easier to parse.
>
> Ok, good point, didn't think about that.
> And agreed, adding remastered StreamIDs as a property to a device node is odd.
>
> > > But all that is needed is to point (once) to each mmu-master in the
> > > SMMU device node. Then you should be able to look up the corresponding
> > > stream IDs in the device node for each mmu-master.
> >
> > Again, you also need to tie in topology information if you go down this
> > route.
I still don't like the approach of having two independend lists that
must be in sync to associate a master with its stream-ids.
Why? Say you have 8 masters for an SMMU with 1 or 2 stream-ids each:
smmu {
...
mmu-masters = <&dma0>, <&dma0>, <&dma1>, <&dma1>,
<&dma2>, <&dma2>, <&dma4>, <&dma4>,
<&dma5>, <&dma6>, <&dma7>, <&dma8>;
stream-ids = <0>, <1>, <2>, <3>,
<4>, <5>, <6>, <7>,
<8>, <9>, <0xa>, <0xb>;
}
Couldn't we use of_phandle_args for this purpose? So your example
+ smmu {
...
+ mmu-masters = <&dma0>,
+ <&dma0>,
+ <&dma1>;
+ stream-ids = <0xd01d>,
+ <0xd01e>,
+ <0xd11c>;
+ };
would look like
dma0 {
...
#stream-id-cells = <2>
...
}
dma1 {
...
#stream-id-cells = <1>
...
}
smmu {
...
mmu-masters = <&dma0 0xd01d 0xd01e
&dma1 0xd11c>,
};
and my example would be converted to
smmu {
...
mmu-masters = <&dma0 0 1 &dma1 2 3 &dma2 4 5
&dma4 6 7 &dma5 8 &dma6 9
&dma7 0xa &dma8 0xb>
...
}
where each master has #stream-id-cells property with value 1 or 2.
And if dma4 has #stream-id-cells = <1>, the parsing code quickly
notifies us about an error whereas such an error can't be noticed
right from the beginning with the two-list-approach. In this example
stream-id 6 belongs to dma3 which was completely ommitted in both
descriptions.
Of course usage of of_phandle_args would restrict the number of
stream-ids per master to 8 (which is currently used as
MAX_PHANDLE_ARGS). But I don't think that this is a restriction in
practice or do you expect to have more than 8 stream-ids per master
(ie. per struct device in Linux)?
Andreas
next prev parent reply other threads:[~2013-05-17 20:16 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-04-12 18:02 [PATCH v2] documentation: iommu: add description of ARM System MMU binding Will Deacon
2013-05-13 9:50 ` Andreas Herrmann
2013-05-13 9:58 ` Will Deacon
2013-05-13 10:41 ` Andreas Herrmann
2013-05-17 20:16 ` Andreas Herrmann [this message]
2013-05-20 10:18 ` Will Deacon
[not found] ` <20130520101841.GK31359-MRww78TxoiP5vMa5CHWGZ34zcgK1vI+I0E9HWUfgJXw@public.gmane.org>
2013-05-21 10:25 ` Andreas Herrmann
2013-05-21 17:33 ` Will Deacon
[not found] ` <20130521173357.GA26251-MRww78TxoiP5vMa5CHWGZ34zcgK1vI+I0E9HWUfgJXw@public.gmane.org>
2013-05-21 18:35 ` Andreas Herrmann
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=20130517201639.GL10369@alberich \
--to=andreas.herrmann@calxeda.com \
--cc=devicetree-discuss@lists.ozlabs.org \
--cc=iommu@lists.linux-foundation.org \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=ohaugan@codeaurora.org \
--cc=will.deacon@arm.com \
/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
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
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).