On 8/25/23 00:25, Geert Uytterhoeven wrote:
Hi Lizhi,
On Thu, Aug 24, 2023 at 8:40 PM Lizhi Hou <lizhi.hou@xxxxxxx> wrote:
On 8/24/23 01:31, Geert Uytterhoeven wrote:
On Tue, 15 Aug 2023, Lizhi Hou wrote:
Currently, in an overlay fdt fragment, it needs to specify the exact
location in base DT. In another word, when the fdt fragment is
generated,
the base DT location for the fragment is already known.
There is new use case that the base DT location is unknown when fdt
fragment is generated. For example, the add-on device provide a fdt
overlay with its firmware to describe its downstream devices. Because it
is add-on device which can be plugged to different systems, its firmware
will not be able to know the overlay location in base DT. Instead, the
device driver will load the overlay fdt and apply it to base DT at
runtime.
In this case, of_overlay_fdt_apply() needs to be extended to specify
the target node for device driver to apply overlay fdt.
int overlay_fdt_apply(..., struct device_node *base);
Signed-off-by: Lizhi Hou <lizhi.hou@xxxxxxx>
Thanks for your patch, which is now commit 47284862bfc7fd56 ("of:
overlay: Extend of_overlay_fdt_apply() in dt-rh/for-next.
--- a/drivers/of/overlay.c
+++ b/drivers/of/overlay.c
@@ -715,6 +730,7 @@ static struct device_node *find_target(struct
device_node *info_node)
/**
* init_overlay_changeset() - initialize overlay changeset from
overlay tree
* @ovcs: Overlay changeset to build
+ * @target_base: Point to the target node to apply overlay
*
* Initialize @ovcs. Populate @ovcs->fragments with node information
from
* the top level of @overlay_root. The relevant top level nodes are the
As an overlay can contain one or more fragments, this means the
base (when specified) will be applied to all fragments, and will thus
override the target-path properties in all fragments.
However, for the use case of an overlay that you can plug into
a random location (and of which there can be multiple instances),
there can really be only a single fragment. Even nodes that typically
live at the root level (e.g. gpio-leds or gpio-keys) must be inserted
below the specified location, to avoid conflicts.
Hence:
1. Should init_overlay_changeset() return -EINVAL if target_base is
specified, and there is more than one fragment?
Maybe allowing more than one fragment make the interface more generic?
For example, it could support the use case that multiple fragments share
the same base node.
Currently, the fragment overlay path is "base node path" + "fragment
target path". Thus, for the structure:
Oh, I had missed that the "fragment target path" is appended,
and thought it was just overridden.
/a/b/c/fragment0
/a/b/d/fagment1
It can be two fragments in one fdt by using
base node path = /a/b
fragment0 target path = /c
fragment1 target path = /d
I am not sure if there will be this kind of use case or not. And I think
it would not be hurt to allow that.
Is there a need for that? Both c and d can be handled as subnodes
in a single fragment if the target path is empty (and see below).
In our use case, we do not need that. I am just not sure if it should be
adding the restriction to limit one fragment here.
Because the fragment target path is appended to the base node path,
each fragment is still applied to a specific location as before. The only
difference is the fragment target path does not need to always start
with "/".
Thanks,
Lizhi
2. Should there be a convention about the target-path property's
contents in the original overlay?
drivers/of/unittest-data/overlay_pci_node.dtso in "[PATCH V13 5/5]
of: unittest: Add pci_dt_testdrv pci driver" uses
target-path="";
which cannot be represented when using sugar syntax.
"/" should work fine, though.
Because the fragment overlay path is "base node path" + "fragment target
path", I may add code to check if "fragment target patch is '/' and
ignore it. I think that would support sugar syntax with only '/' specified.
That makes sense.
Thanks!
Gr{oetje,eeting}s,
Geert
