On 08/01/25 13:37, Herve Codina wrote:
Hi Ayush,
On Wed, 8 Jan 2025 13:06:03 +0530
Ayush Singh <ayush@xxxxxxxxxxxxxxx> wrote:
On 10/12/24 16:25, Herve Codina wrote:
Hi Ayush,
On Tue, 10 Dec 2024 15:26:44 +0530
Ayush Singh <ayush@xxxxxxxxxxxxxxx> wrote:
On 10/12/24 15:11, Herve Codina wrote:
Hi Ayush,
On Tue, 10 Dec 2024 14:52:22 +0530
Ayush Singh <ayush@xxxxxxxxxxxxxxx> wrote:
...
What is the reason for not using symbols directly as described here [3]?
I do like this approach since it does not pollute the global symbols.
Just want to know if there are any other reasons for it.
Modifying the __symbols__ node at runtime (adding / removing properties in
it) exposes memory leaks if __symbols__ already exist in the live DT.
This __symbols__ node exist if the dtb was compiled with '-@' or if you
chain the overlay (i.e. __symbols__ node created by the first overlay).
Yeah, that is a problem, specially in a setup which might involve
hot-plugging.
I think also that some conflicts can appears. What happens if you want to
add a new label but this label is already present for some other purpose?
I do not think that actually is a problem. As described in the original
patch [0], the symbol and connector overlay is supposed to be applied as
a group (overwriting any conflicting symbols in the process).
The reason why this is not a problem is that `__symbols__` are only used
to resolve the phandles (overlays do not support path references yet),
but do not really have a purpose in the livetree (at least far as I
know, but I can be wrong).
Best regards,
Hervé
[0]: https://lore.kernel.org/lkml/20240702164403.29067-1-afd@xxxxxx/
Also, in your first overlay (adding symbols in __sympbols__ node), you have
something like:
GROVE_PIN1_MUX_I2C_SCL = "/bus@f0000/pinctrl@f4000/grove-i2c-pins";
If I understood correctly, other overlays will have GROVE_PIN1_MUX_I2C_SCL
as unresolved symbols and will use GROVE_PIN1_MUX_I2C_SCL to reference the
grove-i2c-pins node.
This unresolved symbol from the overlay is resolved thanks to the __symbols__
table where you added GROVE_PIN1_MUX_I2C_SCL (first overlay operation).
In order to work, you need to have a phandle property set in the
grove-i2c-pins node.
This is done by dtc when you compile the dtb containing the grove-i2c-pins
node (i.e. k3-am625-beagleplay.dts)
The phandle property will be set only if:
- a label for grove-i2c-pins already exist and -@ option is used
or
- a label for grove-i2c-pins already exist and it is referenced as a phandle
in the dts (k3-am625-beagleplay.dts).
Otherwise, dtc will not create the phandle property and without this
property, the symbol resolution will not be correct.
Best regards,
Hervé
Hello Hervé
Thanks for the clarification. things have changed a bit since the last
message and it seems like trying to add path reference support to
overlays is not the best way forward [0]. So I would love to help move
this approach forward.
I do have a question regarding this approach, so here I go:
Can the `export-symbols` node be added to devicetree spec and be
resolved by the devicetree compiler (and fdtoverlay) instead of being
runtime resolution.
Of course, a solution with fdtoverlay is welcome but it should not fully
replace the runtime resolution. In our case, we need runtime resolution
because the overlay is loaded by a driver.
Both resolutions (fdtoverlay and runtime) should work.
I see, it seems linux does not use libfdt for applying overlays internally.
To get some context, I would like to share the addon-board overlays
between ZephyrRTOS and Linux kernel. I would be happy to try adding
support to dtc compiler for it. I am also tagging David Gibson (dtc
maintainer) in this discussion since he also had some ideas regarding
the feasibility and pitfalls of adding it to devicetree compiler (and spec).
[0]:
https://lore.kernel.org/devicetree-compiler/6b2dba90-3c52-4933-88f3-b47f96dc7710@xxxxxxxxxxxxxxx/T/#m900b5ca13cfc28396d4d46d9c3130a7070fa8c90
Best regards,
Ayush Singh
Thanks for your help proposal!
Best regards,
Hervé
I will experiment with adding support to dtc and see how things look.
Hopefully, 2025 is the year of addon board support.
Best regards,
Ayush Singh
