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

quoted

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.

quoted

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

quoted

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.

quoted

device not ready.

Because for cpufreq, no need use fw_devlink. So bypass setting

fwnode

quoted

for scmi cpufreq device.

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

quoted

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

quoted

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,

quoted

 	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"))

quoted

+		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.

Thanks,
Peng.
.

--
Best regards,
Dhruva Gole [off-list ref]