linux-kernel - Re: [PATCH V2] firmware: arm_scmi: bus: bypass set fwnode for scmi cpufreq

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Message-ID: <Zrt3P1FH13edqjoC@pluto>
Date: Tue, 13 Aug 2024 16:09:51 +0100
From: Cristian Marussi <cristian.marussi@....com>
To: Peng Fan <peng.fan@....com>
Cc: Cristian Marussi <cristian.marussi@....com>,
	Dhruva Gole <d-gole@...com>,
	"Peng Fan (OSS)" <peng.fan@....nxp.com>,
	"saravanak@...gle.com" <saravanak@...gle.com>,
	"sudeep.holla@....com" <sudeep.holla@....com>,
	"linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"arm-scmi@...r.kernel.org" <arm-scmi@...r.kernel.org>
Subject: Re: [PATCH V2] firmware: arm_scmi: bus: bypass set fwnode for scmi
 cpufreq

On Tue, Aug 13, 2024 at 01:52:30PM +0000, Peng Fan wrote:
> > Subject: Re: [PATCH V2] firmware: arm_scmi: bus: bypass set fwnode
> > for scmi cpufreq
> > 
> > On Tue, Aug 13, 2024 at 10:25:31AM +0000, Peng Fan wrote:
> > > > Subject: Re: [PATCH V2] firmware: arm_scmi: bus: bypass set
> > fwnode
> > > > for scmi cpufreq
> > > >
> > > > On Jul 29, 2024 at 15:03:25 +0800, Peng Fan (OSS) wrote:
> > > > > From: Peng Fan <peng.fan@....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
> > > >
> > > > The commit message itself seems very specific to some platform to
> > me.
> > > > What about platforms that don't atall have a GPU? Why would
> > they
> > > > care about this?
> > >
> > > It is a generic issue if a platform has performance domain to serve
> > > scmi cpufreq and device performance level.
> > >
> > > >
> > > > > device not ready.
> > > > >
> > > > > Because for cpufreq, no need use fw_devlink. So bypass setting
> > > > fwnode
> > > > > for scmi cpufreq device.
> > > > >
> > > > > Fixes: 96da4a99ce50 ("firmware: arm_scmi: Set fwnode for the
> > > > > scmi_device")
> > > > > Signed-off-by: Peng Fan <peng.fan@....com>
> > > > > ---
> > > > >
> > > > > V2:
> > > > >  Use A!=B to replace !(A == B)
> > > > >  Add fixes tag
> > > > >  This might be a workaround, but since this is a fix, it is simple
> > > > > for backporting.
> > > >
> > > > More than a workaround, it feels like a HACK to me.
> > > >
> > > > >
> > > > > V1:
> > > > >
> > > > >
> > > > >
> > > > >  drivers/firmware/arm_scmi/bus.c | 3 ++-
> > > > >  1 file changed, 2 insertions(+), 1 deletion(-)
> > > > >
> > > > > diff --git a/drivers/firmware/arm_scmi/bus.c
> > > > > b/drivers/firmware/arm_scmi/bus.c index
> > > > 96b2e5f9a8ef..be91a82e0cda
> > > > > 100644
> > > > > --- a/drivers/firmware/arm_scmi/bus.c
> > > > > +++ b/drivers/firmware/arm_scmi/bus.c
> > > > > @@ -395,7 +395,8 @@ __scmi_device_create(struct
> > device_node
> > > > *np, struct device *parent,
> > > > >  	scmi_dev->id = id;
> > > > >  	scmi_dev->protocol_id = protocol;
> > > > >  	scmi_dev->dev.parent = parent;
> > > > > -	device_set_node(&scmi_dev->dev, of_fwnode_handle(np));
> > > > > +	if ((protocol != SCMI_PROTOCOL_PERF) || strcmp(name,
> > > > "cpufreq"))
> > > > > +		device_set_node(&scmi_dev->dev,
> > > > of_fwnode_handle(np));
> > > >
> > > > I kind of disagree with the idea here to be specific about the
> > > > PROTOCOL_PERF or cpufreq. This is a generic arm scmi bus driver
> > right?
> > > > Why bring in specific code into a bus driver? We will never fix the
> > > > actual root cause of the issue this way.
> > >
> > > The root cause is fwnode devlink only supports one fwnode, one
> > device.
> > > 1:1 match. But current arm scmi driver use one fwnode for two
> > devices.
> > >
> > > If your platform has scmi cpufreq and scmi device performance
> > domain,
> > > you might see that some devices are consumer of scmi cpufreq, but
> > > actually they should be consumer of scmi device performance
> > domain.
> > >
> > > I not have a good idea that this is fw devlink design that only allows
> > > 1 fwnode has 1 device or not. If yes, that arm scmi should be fixed.
> > > If not, fw devlink should be updated.
> > >
> > > The current patch is the simplest method for stable tree fixes as I
> > > could work out.
> > 
> > So this is the same root cause at the end of the issues you had with
> > IMX pinctrl coexistence...i.e. the SCMI stack creates scmi devices that
> > embeds the protocol node, BUT since you can have multiple
> > device/drivers doing different things on different resources within the
> > same protocol you can end with 2 devices having the same embedded
> > device_node, since we dont really have anything else to use as
> > device_node, I rigth ?
> 
> I think, yes. And you remind me that with PINCTRL_SCMI and
> CONFIG_PINCTRL_IMX_SCMI both enabled, the scmi pinctrl node
> will only take one to set the fwnode device pointer depends on
> the order to run __scmi_device_create.
> 
> So not only perf, pinctrl also has issue here, fwnode devlink will
> not work properly for pinctrl/perf.

...mmm ... the standard generic Pinctrl driver and the IMX Pintrcl are
mutually exclusive in the code (@probe time) itself as far as I can remember
about what you did, so why devlink should have that issue there ?
Have you seen any issue in this regards while having loaded pinctrl_scmi
and pinctrl_imx_scmi ?

I want to have a better look next days about this devlink issue that you
reported...it still not clear to me...from device_link_add() docs, it
seems indeed that it will return the old existing link if a link exist
already between that same supplier/consumer devices pair....but from the
code (at first sight) it seems that the check is made agains the devices
not their embeded device_nodes, but here (and in pinctrl/imx case) you will
have 2 distinct consumer devices (with same device_node)...I may have
missed something in your exaplanation....

Thanks,
Cristian