RE: [PATCH V2] firmware: arm_scmi: bus: bypass set fwnode for scmi cpufreq

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:

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Subject: Re: [PATCH V2] firmware: arm_scmi: bus: bypass set

fwnode

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for scmi cpufreq

On Tue, Aug 13, 2024 at 10:25:31AM +0000, Peng Fan wrote:

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Subject: Re: [PATCH V2] firmware: arm_scmi: bus: bypass set

fwnode

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for scmi cpufreq

On Jul 29, 2024 at 15:03:25 +0800, Peng Fan (OSS) wrote:

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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

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scmi

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devices will be created. But the fwnode->dev could only point
to one

device.

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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).

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But actually the performance domain user device, such as GPU,

should

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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.

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What about platforms that don't atall have a GPU? Why would

they

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care about this?

It is a generic issue if a platform has performance domain to
serve scmi cpufreq and device performance level.

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device not ready.

Because for cpufreq, no need use fw_devlink. So bypass

setting

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fwnode

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for scmi cpufreq device.

Fixes: 96da4a99ce50 ("firmware: arm_scmi: Set fwnode for

the

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scmi_device")
Signed-off-by: Peng Fan <peng.fan@nxp.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.

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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

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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

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*np, struct device *parent,

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 	scmi_dev->id = id;
 	scmi_dev->protocol_id = protocol;
 	scmi_dev->dev.parent = parent;
-	device_set_node(&scmi_dev->dev,

of_fwnode_handle(np));

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+	if ((protocol != SCMI_PROTOCOL_PERF) ||

strcmp(name,

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"cpufreq"))

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+		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

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right?

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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.

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1:1 match. But current arm scmi driver use one fwnode for two

devices.

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If your platform has scmi cpufreq and scmi device performance

domain,

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you might see that some devices are consumer of scmi cpufreq,

but

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actually they should be consumer of scmi device performance

domain.

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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

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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

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take one to set the fwnode device pointer depends on the order to

run

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__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 ?

No. it works well in my setup. I am just worried that there might
be issues because fwnode only has one dev pointer, see
device_add.

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....

It might be false alarm for pinctrl, but it is true issue for perf.

Regards,
Peng.

Thanks,
Cristian