Message-ID: <537A3EC4.9060801@ahsoftware.de>
Date:	Mon, 19 May 2014 19:26:28 +0200
From:	Alexander Holler <holler@...oftware.de>
To:	Jon Loeliger <loeliger@...il.com>
CC:	Tomasz Figa <tomasz.figa@...il.com>, linux-kernel@...r.kernel.org,
	devicetree@...r.kernel.org, Jon Loeliger <jdl@....com>,
	Russell King <linux@....linux.org.uk>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Rob Herring <robh+dt@...nel.org>,
	Grant Likely <grant.likely@...aro.org>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [RFC PATCH 1/9] dt: deps: dtc: Automatically add new property
 'dependencies' which contains a list of referenced phandles

Am 19.05.2014 17:49, schrieb Jon Loeliger:
> [ Crap.  Sorry about the duplicate post.  Stupid HTML; didn't hit the
> lists. -- jdl ]
>
>
>> What's still questionable about the patches for dtc is if dependencies to
>> devices and not just drivers should be included in the new property
>> dependencies too.
>
> I don't think the DTC should have any semantic knowledge of why these
> dependency arcs are being added to the graph.  Sure, it could be that
> different types of arcs are added, and that the total dependency graph
> travels multiple such arc types to obtains some valid topological sort,
> but the DTC itself should just not care.

I will remove those policies (which means including all dependencies). 
As said below, I already thought it was evil premature optimization (I 
did in order to make the graph a bit smaller and to save some bytes). 
(No date, it isn't a paid project so I will do it whenever I feel good 
to do so).

> After saying that, there are likely semantic checks that could be added to
> ensure some policy about those arcs was followed.  Separate the
> implementation from the policy.  There is already plenty of discussion
> down that line within the DTC ongoing.

Hmm, discussion about what? Those dependencies or about semantic checks?

Btw., if someone has a problem with the necessary time to do the 
topological sort at boot time (needs a few ms on a single core omap with 
600 MHz), there could be an additional option to add a new property 
which includes the whole (already topological sorted) list. That 
wouldn't be much effort. But currently I don't think any DT enabled 
device is in need of having to avoid doing the topological sort itself.

Regards,

Alexander Holler

>
> HTH,
> jdl
>
>
> On Mon, May 19, 2014 at 7:35 AM, Alexander Holler <holler@...oftware.de>wrote:
>
>> Am 17.05.2014 14:16, schrieb Tomasz Figa:
>>
>>
>>   References to phandles of parent or child nodes will not be added to this
>>>> property, because this information is already contained in the blob (in
>>>> the
>>>> form of the tree itself).
>>>>
>>>
>>> I wonder if we shouldn't be including them too for consistency related
>>> reasons, so we have all the necessary information in one place.
>>> References to child nodes are great recipes for cycles, though...
>>>
>>> No strong opinion, though, just an idea.
>>>
>>
>> As said, they are already in the tree itself. And they are already
>> included in the graph (these are the black edges), so they just don't
>> appear in the property dependencies.
>>
>>
>>
>>>
>>>> No dependencies to disabled nodes will be added.
>>>>
>>>>
>>> Same here. IMHO it might be wise to let the parsing entity (e.g. kernel)
>>> decide whether to ignore a dependency to disabled node or not.
>>>
>>> Otherwise, I like the simplicity of compile-time dependency list
>>> creation. Quite a nice work.
>>>
>>
>> Thanks.
>>
>> What's still questionable about the patches for dtc is if dependencies to
>> devices and not just drivers should be included in the new property
>> dependencies too. My current assumption is that all devices belonging to
>> one and the same driver don't have dependencies between each other. In
>> other words the order in which devices will be attached to one and the same
>> driver isn't important. If that assumption is correct it would be possible
>> to just attach all devices belonging to a driver after the driver was
>> loaded (also I haven't that done in my patches).
>>
>> And thinking about that again, I think I was wrong and doing so have been
>> some kind of evil premature optimization I did in order to spare a few
>> dependencies/edges. But changing this can done by removing a few lines in
>> the code for dtc (patch 1).
>>
>> Regards,
>>
>> Alexander Holler
>>
>>
>>
>> _______________________________________________
>> linux-arm-kernel mailing list
>> linux-arm-kernel@...ts.infradead.org
>> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
>>
>

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