Hi On Jan 22, 2013, at 5:50 AM, David Gibson wrote: > On Fri, Jan 04, 2013 at 09:31:10PM +0200, Pantelis Antoniou wrote: >> Introduce DT overlay support. >> Using this functionality it is possible to dynamically overlay a part of >> the kernel's tree with another tree that's been dynamically loaded. >> It is also possible to remove node and properties. >> >> Signed-off-by: Pantelis Antoniou <panto@xxxxxxxxxxxxxxxxxxxxxxx> >> --- >> Documentation/devicetree/overlay-notes.txt | 179 +++++++ >> drivers/of/Kconfig | 10 + >> drivers/of/Makefile | 1 + >> drivers/of/overlay.c | 831 +++++++++++++++++++++++++++++ >> include/linux/of.h | 107 ++++ >> 5 files changed, 1128 insertions(+) >> create mode 100644 Documentation/devicetree/overlay-notes.txt >> create mode 100644 drivers/of/overlay.c >> >> diff --git a/Documentation/devicetree/overlay-notes.txt b/Documentation/devicetree/overlay-notes.txt >> new file mode 100644 >> index 0000000..5289cbb >> --- /dev/null >> +++ b/Documentation/devicetree/overlay-notes.txt >> @@ -0,0 +1,179 @@ >> +Device Tree Overlay Notes >> +------------------------- >> + >> +This document describes the implementation of the in-kernel >> +device tree overlay functionality residing in drivers/of/overlay.c and is a >> +companion document to Documentation/devicetree/dt-object-internal.txt[1] & >> +Documentation/devicetree/dynamic-resolution-notes.txt[2] >> + >> +How overlays work >> +----------------- >> + >> +A Device Tree's overlay purpose is to modify the kernel's live tree, and >> +have the modification affecting the state of the the kernel in a way that >> +is reflecting the changes. > > Um.. I'm having a great deal of trouble parsing that sentence. > >> +Since the kernel mainly deals with devices, any new device node that result >> +in an active device should have it created while if the device node is either >> +disabled or removed all together, the affected device should be deregistered. >> + >> +Lets take an example where we have a foo board with the following base tree >> +which is taken from [1]. >> + >> +---- foo.dts ----------------------------------------------------------------- >> + /* FOO platform */ >> + / { >> + compatible = "corp,foo"; >> + >> + /* shared resources */ >> + res: res { >> + }; >> + >> + /* On chip peripherals */ >> + ocp: ocp { >> + /* peripherals that are always instantiated */ >> + peripheral1 { ... }; >> + } >> + }; >> +---- foo.dts ----------------------------------------------------------------- >> + >> +The overlay bar.dts, when loaded (and resolved as described in [2]) should >> + >> +---- bar.dts ----------------------------------------------------------------- >> +/plugin/; /* allow undefined label references and record them */ >> +/ { >> + .... /* various properties for loader use; i.e. part id etc. */ >> + fragment@0 { >> + target = <&ocp>; >> + __overlay__ { >> + /* bar peripheral */ >> + bar { >> + compatible = "corp,bar"; >> + ... /* various properties and child nodes */ >> + } >> + }; >> + }; >> +}; >> +---- bar.dts ----------------------------------------------------------------- >> + >> +result in foo+bar.dts >> + >> +---- foo+bar.dts ------------------------------------------------------------- >> + /* FOO platform + bar peripheral */ >> + / { >> + compatible = "corp,foo"; >> + >> + /* shared resources */ >> + res: res { >> + }; >> + >> + /* On chip peripherals */ >> + ocp: ocp { >> + /* peripherals that are always instantiated */ >> + peripheral1 { ... }; >> + >> + /* bar peripheral */ >> + bar { >> + compatible = "corp,bar"; >> + ... /* various properties and child nodes */ >> + } >> + } >> + }; >> +---- foo+bar.dts ------------------------------------------------------------- >> + >> +As a result of the the overlay, a new device node (bar) has been created >> +so a bar platform device will be registered and if a matching device driver >> +is loaded the device will be created as expected. > > Hrm. This all seems rather complicated. Maybe it needs to be, but > I'm not entirely convinced yet. > > One other point - both of these patches are assuming that the overlay > is in the "live tree" format, but it still needs a bunch of extra > mangling. Would it simplify things to just go straight from the > overlay in flat tree form to modifications to the system-wide live > tree. Sorry, I can't parse this. You mean apply the overlay without converting to live tree format? > > -- > David Gibson | I'll have my music baroque, and my code > david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_ > | _way_ _around_! > http://www.ozlabs.org/~dgibson -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html