No support of platform device instance id?

[Grant Likely]

On Thu, Mar 17, 2011 at 12:31:15PM +0800, Shawn Guo wrote:
> On Wed, Mar 16, 2011 at 05:05:00PM -0600, Grant Likely wrote:
> > 
> [...]
> > I'd like to have feedback on the new code to make sure that the model
> > is sane.  There are some fiddly code it there which is used to match
> > platform_device registrations to nodes in the device tree.  I *think*
> > it makes sense, but I'd like to hear other opinions.
> > 
> Binding platform_device with of_node via resources matching seems a
> little fiddly, but your implementation looks solid to me.  I made a
> quick scan on all the platform_device registration under
> arch/arm/plat-mxc/devices, nothing would be broken, only except
> platform-gpio_keys which is not an on-chip device.

Right; and doing it this way doesn't make sense for anything that is
board/system specific because if the board is using the DT, then it is
simpler and more reliable to avoid the matching heuristic entirely.

> Looking at the code, I'm wondering how the binding of resource type
> IORESOURCE_DMA looks like.  I'm seeing some platform_device is using
> this flag to tell dma channel fixed for the device.  I'm not sure if
> it can be fit in property 'dma-ranges'.  And I only see IORESOURCE_MEM
> and IORESOURCE_IRQ being used in the matching model.

The matching is simply a heuristic that makes a best guess about how
how device nodes line up with platform_device registrations.  Right
now the heuristic is to look at the register ranges and irqs described
in the node and make sure that each of them are listed in the
platform_device.  If the platform_device has additional resources,
then it simply ignores them.  That seems to be sufficient for accurate
matching, but I won't know for sure until people start using it.

If there are situations where the heuristic does not work, then I'd
like to know what they are so that the algorithm can be fixed, or in
the absolute worst case implement workaround logic.

One option I'm considering which would improve the accuracy of the
heuristic is to add a 'char *of_compatible' field to struct
platform_device.  Then platform_devices could optionally be tagged
with the compatible value that must be present in order to be matched
with a node.

I definitely want feedback on the matching heuristic!

g.