Re: [PATCH 3/8] firmware: arm_scmi: Convert OF-only paths to generic fwnode in SCMI core

Sudeep Holla
2025-10-21T09:26:10Z

On Mon, Oct 20, 2025 at 06:29:49PM +0100, Jonathan Cameron wrote:
> On Fri, 17 Oct 2025 14:23:46 +0100
> Sudeep Holla <sudeep.holla@arm.com> wrote:
>
> > Switch SCMI core plumbing from struct device_node* to struct
> > fwnode_handle* so transports and core code work with both DT and
> > ACPI firmware descriptions.
> >
> > This change:
> > - Replaces of_* property lookups with fwnode_property_*() helpers.
> > - Switches child enumeration to
> > fwnode_for_each_available_child_node_scoped().
> > - Plumbs fwnode through the SCMI device creation and channel setup
> > paths and updates transport ->chan_available() signatures to take a
> > fwnode.
> > - Stores the per-protocol child fwnodes in info->active_protocols so
> > the core can later locate the descriptor for a given protocol ID.
> > - Update mailbox/optee/smc/virtio transports to accept fwnode and
> > map to OF nodes where needed
> >
> > DT-only transports (mailbox/optee/smc) still parse DT properties by
> > mapping the fwnode back to an OF node; on non-DT (e.g. ACPI) systems
> > these transports will report no channel available.
> >
> > This refactor is a prerequisite for adding an ACPI-first transport like
> > PCC and brings the SCMI core closer to DT/ACPI parity. This is a mechanical
> > step towards firmware-node neutrality; DT users continue to work unchanged,
> > and ACPI paths can be enabled on top.
> >
> > No functional change is expected on DT platforms; ACPI platforms can now
> > discover and participate in SCMI where a suitable transport is present.
> >
> > Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
> Hi Sudeep
>
> A few comments inline. The reference counting on fwnodes gets a bit complex in
> here so my review more or less skips that bit (it's end of day!)
>

No, I had exactly same thoughts and I did mention about this briefly to
Cristian before posting as I couldn't follow the existing refcounting 🙁.
I need to catch up with Cristian and align ourselves before the next version.

> > diff --git a/drivers/firmware/arm_scmi/driver.c b/drivers/firmware/arm_scmi/driver.c
> > index bd56a877fdfc..bc5fea11b5db 100644
> > --- a/drivers/firmware/arm_scmi/driver.c
> > +++ b/drivers/firmware/arm_scmi/driver.c
>
> > @@ -2820,7 +2820,7 @@ static int scmi_chan_destroy(int id, void *p, void *idr)
> > struct scmi_info *info = handle_to_scmi_info(cinfo->handle);
> > struct scmi_device *sdev = to_scmi_dev(cinfo->dev);
> >
> > - of_node_put(cinfo->dev->of_node);
> > + fwnode_handle_put(dev_fwnode(cinfo->dev));
>
> This may follow on from earlier thing about device_set_node().
> I think this is freeing a reference that will never have been gotten if you
> follow what I suggest there. Note that I'm fairly sure it was never
> gotten for acpi anyway. However this might be a different fwnode, I'm lost
> on that front.
>

Even I was lost and wanted to revisit this whole reference counting once again
before these changes find its way upstream.

> > scmi_device_destroy(info->dev, id, sdev->name);
> > cinfo->dev = NULL;
> > }
>
> > @@ -3118,8 +3119,8 @@ static const struct scmi_desc *scmi_transport_setup(struct device *dev)
> > trans->desc.max_msg);
> >
> > /* System wide atomic threshold for atomic ops .. if any */
> > - if (!of_property_read_u32(dev->of_node, "atomic-threshold-us",
> > - &trans->desc.atomic_threshold))
> > + if (!fwnode_property_read_u32(dev_fwnode(dev), "atomic-threshold-us",
>
> device_property_read_u32() Same for all the other places where the fwnode
> is simple dev_fwnode(dev) and there is a suitable helper.
>

Ah OK, didn't notice that, thanks for the pointer.

>
> > + &trans->desc.atomic_threshold))
> > dev_info(dev,
> > "SCMI System wide atomic threshold set to %u us\n",
> > trans->desc.atomic_threshold);
>
> > @@ -3262,10 +3262,10 @@ static int scmi_probe(struct platform_device *pdev)
> >
> > scmi_enable_matching_quirks(info);
> >
> > - for_each_available_child_of_node(np, child) {
> > + fwnode_for_each_available_child_node_scoped(dev_fwnode(dev), child) {
> I don't think there is an exit path in here, so this is functionally the same
> as the non scoped version.
>

I get you point.

> Also, if you are gong to use dev_fwnode use
> device_for_each_child_node() and don't worry about the available.
> I think the patch merged that made device_for_each_child_node() only
> consider the available ones for all firmware types.
>

Not sure if I fully understand yet, but will revisit this again before
next version.

> > u32 prot_id;
> >
> > - if (of_property_read_u32(child, "reg", &prot_id))
> > + if (fwnode_property_read_u32(child, "reg", &prot_id))
> > continue;
> >
> > if (!FIELD_FIT(MSG_PROTOCOL_ID_MASK, prot_id))
> > @@ -3278,10 +3278,11 @@ static int scmi_probe(struct platform_device *pdev)
> > }
> >
> > /*
> > - * Save this valid DT protocol descriptor amongst
> > + * Save this valid fwnode protocol descriptor amongst
> > * @active_protocols for this SCMI instance/
> > */
> > - ret = idr_alloc(&info->active_protocols, child,
> > + ret = idr_alloc(&info->active_protocols,
> > + fwnode_handle_get(child),
>
> This change is a little subtle to be buried in here and I'm fairly sure
> it is an unintended functional change. If idr_alloc() fails the continue
> and loop iterator magic, will drop the reference held by the loop but
> not this one. So it will leak a reference.
>
> If this does make sense, do it in a precursor patch before changing away
> from of only.
>

Indeed, I can't recall why I have added the reference counting here. It can
be dropped, will give it another thought to see if anything strikes my mind.

> > prot_id, prot_id + 1, GFP_KERNEL);
> > if (ret != prot_id) {
> > dev_err(dev, "SCMI protocol %d already activated. Skip\n",
> > @@ -3289,7 +3290,6 @@ static int scmi_probe(struct platform_device *pdev)
> > continue;
> > }
> >
> > - of_node_get(child);
> > scmi_create_protocol_devices(child, info, prot_id, NULL);
> > }
> >
>

--
Regards,
Sudeep