On 02/08/2013 05:05 PM, Sylwester Nawrocki wrote:

On 02/09/2013 12:21 AM, Stephen Warren wrote:

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On 02/08/2013 04:16 PM, Sylwester Nawrocki wrote:

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On 02/07/2013 12:40 AM, Stephen Warren wrote:

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diff --git
a/Documentation/devicetree/bindings/media/soc/samsung-fimc.txt
b/Documentation/devicetree/bindings/media/soc/samsung-fimc.txt

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+Samsung S5P/EXYNOS SoC Camera Subsystem (FIMC)
+----------------------------------------------

...

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+For every fimc node a numbered alias should be present in the
aliases node.
+Aliases are of the form fimc<n>, where<n>   is an integer (0...N)
specifying
+the IP's instance index.

Why? Isn't it up to the DT author whether they care if each fimc
node is
assigned a specific identification v.s. whether identification is
assigned automatically?

There are at least three different kinds of IPs that come in multiple
instances in an SoC. To activate data links between them each instance
needs to be clearly identified. There are also differences between
instances of same device. Hence it's important these aliases don't have
random values.

Some more details about the SoC can be found at [1]. The aliases are
also already used in the Exynos5 GScaler bindings [2] in a similar way.

Hmmm. I'd expect explicit DT properties to represent the
instance-specific "configuration", or even different compatible values.
Relying on the alias ID seems rather indirect; what if in e.g.
Exynos6/... the mapping from instance/alias ID to feature set changes.
With explicit DT properties, that'd just be a .dts change, whereas by
requiring alias IDs now, you'd need a driver change to support this.

In the initial version of this patch series I used cell-index property,
but then Grant pointed out in some other mail thread it should be
avoided. Hence I used the node aliases.

To me, using cell-index is semantically equivalent to using the alias ID.

Different compatible values might not work, when for example there
are 3 IPs out of 4 of one type and the fourth one of another type.
It wouldn't even by really different types, just quirks/little
differences between them, e.g. no data path routed to one of other IPs.

I was thinking of using feature-/quirk-oriented properties. For example,
if there's a port on 3 of the 4 devices to connect to some other IP
block, simply include a boolean property to indicate whether that port
is present. It would be in 3 of the nodes but not the 4th.

Then to connect e.g. MIPI-CSIS.0 to FIMC.2 at run time an index of the
MIPI-CSIS needs to be written to the FIMC.2 data input control register.
Even though MIPI-CSIS.N are same in terms of hardware structure they still
need to be distinguished as separate instances.

Oh, so you're using the alias ID as the value to write into the FIMC.2
register for that. I'm not 100% familiar with aliases, but they seem
like a more user-oriented naming thing to me, whereas values for hooking
up intra-SoC routing are an unrelated namespace semantically, even if
the values happen to line up right now. Perhaps rather than a Boolean
property I mentioned above, use a custom property to indicate the ID
that the FIMC.2 object knows the MIPI-CSIS.0 object as? While this seems
similar to using cell-index, my *guess* is that Grant's objection to
using cell-index was more based on re-using cell-index for something
other than its intended purpose than pushing you to use an alias ID
rather than a property.

After all, what happens in some later SoC where you have two different
types of module that feed into the common module, such that type A
sources have IDs 0..3 in the common module, and type B sources have IDs
4..7 in the common module - you wouldn't want to require alias ISs 4..7
for the type B DT nodes.