On 06/06/17 00:20, Frank Rowand wrote:
> 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.
Digging a little bit deeper into the suggestion by Pantelis, I don't like
that approach either. It is still rather hacky.
>
>>
>> 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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