On 06/05/17 05:59, Stefani Seibold wrote:
> From: Stefani Seibold <stefani@xxxxxxxxxxx>
>
> This patch enables external references for symbols which are not
> exported by the current device tree. For example
>
> // RASPI example (only for testing)
> /dts-v1/;
> /plugin/;
>
> / {
> compatible = "brcm,bcm2835", "brcm,bcm2708", "brcm,bcm2709";
>
> fragment@0 {
> target-path = "/soc/i2s@7e203000";
> __overlay__ {
> #address-cells = <0x00000001>;
> #size-cells = <0x00000001>;
> test = "test";
> timer = <&timer>;
> };
> };
>
> __external_symbols__ {
> timer = "/soc/timer@7e003000";
> };
> };
My hope is that the dtc compiler will stop supporting specification of the
__symbols__ node in dts source, and only generate it automatically in the dtb.
That change to dtc would not allow any node name specified in a dts to begin
with an underscore. Thus node __external_symbols__ would not be allowed.
>
> The "timer" symbol is not exported by the RASPI device tree, because it is
> missing in the __symbols__ section of the device tree.
>
> In case of the RASPI device tree this could be simple fixed by modifing
> the device tree source, but when the device tree is provided by a closed
> source BIOS this kind of missing symbol could not be fixed.
Is there a real example of this issue, or is this a theoretical concern?
If this is a real example, we should be discouraging such behavior.
The suggestion by Pantelis should work, but that is just a hack to get
you out of a bad situation, not a good practice.
>
> An additional benefit is to override a (possible broken) symbol exported
> by the currect live device tree.
>
> The patch is based and tested on linux 4.12-rc3.
>
> Signed-off-by: Stefani Seibold <stefani.seibold.ext@xxxxxxxxxx>
> Signed-off-by: Stefani Seibold <stefani@xxxxxxxxxxx>
> ---
> drivers/of/overlay.c | 19 +++++++++++++++++++
> drivers/of/resolver.c | 27 ++++++++++++++++++++++-----
> 2 files changed, 41 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/of/overlay.c b/drivers/of/overlay.c
> index 7827786718d8..de6516ea0fcd 100644
> --- a/drivers/of/overlay.c
> +++ b/drivers/of/overlay.c
< snip >
-Frank
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