On Sat, Dec 13, 2014 at 5:46 PM, Sebastian Reichel [off-list ref] wrote:

Hi,

On Fri, Dec 12, 2014 at 11:59:20AM +0000, Grant Likely wrote:

quoted

[...]

quoted

--- a/Documentation/devicetree/bindings/serial/of-serial.txt
+++ b/Documentation/devicetree/bindings/serial/of-serial.txt

@@ -39,6 +39,10 @@ Optional properties:
   driver is allowed to detect support for the capability even without this
   property.

+Optional child node:
+- a platform device listed as a child node will be probed and
+  powered-on whenever the tty is in use (open).
+

The biggest concern I have is what happens to nodes that already have
child devices that /don't/ match this use case? It is possible that some
UART nodes already have a child node used to store other data. There are
two ways to handle this; 1) add a new bool property that indicates the
child nodes are tty slave devices, or 2) Make each uart driver
explicitly enable the feature so that driver authors can check if it is
a problem for that device. I personally would suggest #1 because then it
can be enabled in generic code.

maybe simple depend on the compatible value? If the UART node has
child nodes to store other random data it should not have a
compatible value?

That's not a given. It is entirely possible that drivers have used
compatible in the child nodes.

However, I may be stirring up trouble for nothing. We could enable it
for all child nodes that have a compatible value, and then blacklist
any parent nodes that want to use a different behaviour. If someone
complains then we will fix it.

g.