Re: [PATCH 1/4] firmware: arm_scmi: bus: Bypass setting fwnode for scmi cpufreq

[Cristian Marussi <cristian.marussi@arm.com>]

On Fri, Dec 27, 2024 at 03:13:06PM +0000, Sudeep Holla wrote:
> On Wed, Dec 25, 2024 at 04:20:44PM +0800, Peng Fan (OSS) wrote:
> > From: Peng Fan <peng.fan@nxp.com>
> >
> > Two drivers scmi_cpufreq.c and scmi_perf_domain.c both use
> > SCMI_PROTCOL_PERF protocol, but with different name, so two scmi devices
> > will be created. But the fwnode->dev could only point to one device.
> >
> > If scmi cpufreq device created earlier, the fwnode->dev will point to
> > the scmi cpufreq device. Then the fw_devlink will link performance
> > domain user device(consumer) to the scmi cpufreq device(supplier).
> > But actually the performance domain user device, such as GPU, should use
> > the scmi perf device as supplier. Also if 'cpufreq.off=1' in bootargs,
> > the GPU driver will defer probe always, because of the scmi cpufreq
> > device not ready.
> >
> > Because for cpufreq, no need use fw_devlink. So bypass setting fwnode
> > for scmi cpufreq device.
> >

Hi,

> > Fixes: 96da4a99ce50 ("firmware: arm_scmi: Set fwnode for the scmi_device")
> > Signed-off-by: Peng Fan <peng.fan@nxp.com>
> > ---
> >  drivers/firmware/arm_scmi/bus.c | 15 ++++++++++++++-
> >  1 file changed, 14 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/firmware/arm_scmi/bus.c b/drivers/firmware/arm_scmi/bus.c
> > index 157172a5f2b577ce4f04425f967f548230c1ebed..12190d4dabb65484543044b4424fbe3b67245466 100644
> > --- a/drivers/firmware/arm_scmi/bus.c
> > +++ b/drivers/firmware/arm_scmi/bus.c
> > @@ -345,6 +345,19 @@ static void __scmi_device_destroy(struct scmi_device *scmi_dev)
> >  	device_unregister(&scmi_dev->dev);
> >  }
> >
> > +static int
> > +__scmi_device_set_node(struct scmi_device *scmi_dev, struct device_node *np,
> > +		       int protocol, const char *name)
> > +{
> > +	/* cpufreq device does not need to be supplier from devlink perspective */
> > +	if ((protocol == SCMI_PROTOCOL_PERF) && !strcmp(name, "cpufreq"))
> > +		return 0;
> >
> 
> This is just a assumption based on current implementation. What happens
> if this is needed. Infact, it is used in the current implementation to
> create a dummy clock provider, so for sure with this change that will
> break IMO.

I agree with Sudeep on this: if you want to exclude some SCMI device from the
fw_devlink handling to address the issues with multiple SCMI devices
created on the same protocol nodes, cant we just flag this requirement here and
avoid to call device_link_add in driver:scmi_set_handle(), instead of
killing completely any possibility of referencing phandles (and having
device_link_add failing as a consequence of having a NULL supplier)

i.e. something like:

@bus.c
------
static int
__scmi_device_set_node(struct scmi_device *scmi_dev, struct device_node *np,
		       int protocol, const char *name)
{
	if ((protocol == SCMI_PROTOCOL_PERF) && !strcmp(name, "cpufreq"))
		scmi_dev->avoid_devlink = true;

	device_set_node(&scmi_dev->dev, of_fwnode_handle(np));
	....


and @driver.c
-------------

static void scmi_set_handle(struct scmi_device *scmi_dev)
{
	scmi_dev->handle = scmi_handle_get(&scmi_dev->dev);
	if (scmi_dev->handle && !scmi_dev->avoid_devlink)
		scmi_device_link_add(&scmi_dev->dev, scmi_dev->handle->dev);
}

.... so that you can avoid fw_devlink BUT keep the device_node NON-null
for the device.

This would mean also restoring the pre-existing explicit blacklisting in
pinctrl-imx to avoid issues when pinctrl subsystem searches by
device_node...

..or I am missing something ?

Thanks,
Cristian