Re: [PATCH] Revert "of: property: fw_devlink: Add support for remote-endpoint"
From: Dmitry Baryshkov
Date: Fri Oct 01 2021 - 21:04:35 EST
On 28/09/2021 04:13, Saravana Kannan wrote:
On Mon, Sep 27, 2021 at 5:56 PM Dmitry Baryshkov
<dmitry.baryshkov@xxxxxxxxxx> wrote:
[Adding Stephen and linux-arm-msm to the CC list, missed on the patch Cc
list]
On 28/09/2021 00:58, Saravana Kannan wrote:
On Mon, Sep 27, 2021 at 1:48 PM Dmitry Baryshkov
<dmitry.baryshkov@xxxxxxxxxx> wrote:
Since the commit f7514a663016 ("of: property: fw_devlink: Add support
for remote-endpoint") Linux kernel started parsing and adding devlinks
for the remote-endpoint properties. However this brings more harm than
good.
For all the remote-endpoints in the graph two links are created. Thus
each and every remote-endpoint ends up in the cyclic graph (instead of
the original intent of catching a cycle of graph + non-graph link):
Yes, I'm well aware of this. I even called this out in the commit
text. This creating of cycles and then catching and relaxing it is
intentional.
https://lore.kernel.org/all/20210330185056.1022008-1-saravanak@xxxxxxxxxx/
What would be the reason two always create a cycle which gives no
additional information? Maybe I'm just misunderstanding this piece of code.
It's basically a tiny bit of busy work. Ulf and I planned to fix it
and we know how to. Just haven't gotten around to it since it doesn't
really break anything.
Regarding your commit message. Even if there is a non-remote-endpoint
dependency, it will be hidden by the remote-endpoint cycle.
That's the point. Because there's no way to tell without the driver
involvement, we basically need to ignore all dependencies between
those two devices pointing at each other.
And another consequence of remote-endpoint loops.
Consider this part part of dmesg. One warning is correct (real cyclic
dependency). Others are remote-endpoint spam. Can you spot, which ones?
[ 7.032225] platform 1d87000.phy: Fixing up cyclic dependency with
1d84000.ufshc
[ 21.760326] platform c440000.spmi:pmic@2:typec@1500: Fixing up cyclic
dependency with c440000.spmi:pmic@2:pmic-tcpm
[ 21.944849] platform c440000.spmi:pmic@2:pdphy@1700: Fixing up cyclic
dependency with c440000.spmi:pmic@2:pmic-tcpm
[ 23.541968] platform a600000.usb: Fixing up cyclic dependency with
c440000.spmi:pmic@2:pmic-tcpm
[ 30.354170] i2c 5-002b: Fixing up cyclic dependency with hdmi-out
It's info, not warning if I'm not mistaken. If that's really a problem
we can make it a debug log. Not the end of the world.
[ 0.381057] OF: remote-endpoint linking /soc@0/geniqup@9c0000/i2c@994000/hdmi-bridge@2b to /soc@0/mdss@ae00000/dsi@ae94000/ports/port@1/endpoint
[ 0.394421] OF: remote-endpoint linking /soc@0/geniqup@9c0000/i2c@994000/hdmi-bridge@2b to /hdmi-out/port/endpoint
[ 0.407007] OF: remote-endpoint linking /soc@0/phy@88e9000 to /soc@0/spmi@c440000/pmic@2/pmic-tcpm/connector/ports/port@0/endpoint@0
[ 0.419648] OF: remote-endpoint linking /soc@0/usb@a6f8800/usb@a600000 to /soc@0/spmi@c440000/pmic@2/pmic-tcpm/ports/port@2/endpoint@0
[ 0.432578] OF: remote-endpoint linking /soc@0/cci@ac4f000/i2c-bus@1/cam1@c0 to /soc@0/camss@ac6a000/ports/port@1/endpoint
[ 0.444450] OF: remote-endpoint linking /soc@0/camss@ac6a000 to /soc@0/cci@ac4f000/i2c-bus@1/cam1@c0/port/endpoint
[ 0.455292] OF: remote-endpoint linking /soc@0/mdss@ae00000/mdp@ae01000 to /soc@0/mdss@ae00000/dsi@ae94000/ports/port@0/endpoint
[ 0.467210] OF: remote-endpoint linking /soc@0/mdss@ae00000/mdp@ae01000 to /soc@0/mdss@ae00000/dsi@ae96000/ports/port@0/endpoint
[ 0.479239] OF: remote-endpoint linking /soc@0/mdss@ae00000/dsi@ae94000 to /soc@0/mdss@ae00000/mdp@ae01000/ports/port@0/endpoint
[ 0.491147] OF: remote-endpoint linking /soc@0/mdss@ae00000/dsi@ae94000 to /soc@0/geniqup@9c0000/i2c@994000/hdmi-bridge@2b/ports/port@0/endpoint
[ 0.504979] OF: remote-endpoint linking /soc@0/spmi@c440000/pmic@2/typec@1500 to /soc@0/spmi@c440000/pmic@2/pmic-tcpm/ports/port@0/endpoint
[ 0.517958] OF: remote-endpoint linking /soc@0/spmi@c440000/pmic@2/pdphy@1700 to /soc@0/spmi@c440000/pmic@2/pmic-tcpm/ports/port@1/endpoint
[ 0.565326] OF: remote-endpoint linking /hdmi-out to /soc@0/geniqup@9c0000/i2c@994000/hdmi-bridge@2b/ports/port@2/endpoint
Under some conditions the device can become it's own supplier,
preventing this device to be probed at all:
I'm not sure this analysis is correct -- this shouldn't be happening.
If you go to the device link folder and cat "sync_state_only", I
expect it to be "1" in this case. Can you confirm that?
It is "1".
Thanks for confirming.
Which means it won't block probing. Yes, the link itself is useless
and it'll get auto deleted once mdss probes and it's easy to not
create it in the first place. But this is definitely not your issue.
$ ls -l /sys/bus/platform/devices/ae00000.mdss/
lrwxrwxrwx 1 root root 0 Aug 4 15:13 consumer:platform:ae00000.mdss -> ../../../virtual/devlink/platform:ae00000.mdss--platform:ae00000.mdss
I think that until of_link can be tought to handle bi-directional links
on its own, we should not parse remote-endpoint properties. Thus the
aforementioned commit should be reverted.
Nak. remote-endpoint parsing is working as intended. I don't think the
analysis is correct.
Can you please enable the logs in all these functions and attach the
log so we can see why it's not probing mdss?
device_link_add
device_links_check_suppliers
func fw_devlink_relax_link
fw_devlink_create_devlink
After doing the analysis, I can confirm that I was too quick regarding
the mdss links preventing it from being probed. Sorry about that.
It all went up to the DP phy having a link with usb-c-connector. I was
running the kernel 5.15-rc1, so your tcpm fix is already present.
However my colleague has disabled the tcpm device (which I did not
notice). So the driver did not call fw_devlink_purge_absent_suppliers().
The devlink still exists:
Let me take a closer look at this before the end of this week. Can you
point me to the exact DT changes that were made that's causing this
issue? It should help me debug the issue. I have a guess on what the
issue might be.
Here is the kernel source:
https://git.linaro.org/people/bryan.odonoghue/kernel.git/log/?h=5.15-rc1-camss-v2
The change that causes PHY driver to silently stop probing, causing an
avalanche of devices not being probed:
https://git.linaro.org/people/bryan.odonoghue/kernel.git/commit/?h=5.15-rc1-camss-v2&id=d0bf3fc47c132968c302965154eeb5c88007fa73
[ 53.426446] platform 88e9000.phy: probe deferral - wait for supplier
connector
However it is not present in the sysfs:
Right, because it's not a device link yet. It's waiting for the device
to show up to create the device link (it has to for the grand scheme
of things to work correctly).
Could you please make it somehow visible that there is a
pending/blocking device link which is not visible yet (or even better
where it is pointing)?
root@qcom-armv8a:~# ls -l /sys/bus/platform/devices/88e9000.phy/
lrwxrwxrwx 1 root root 0 Aug 4 15:13
consumer:platform:a600000.usb ->
../../../virtual/devlink/platform:88e9000.phy--platform:a600000.usb
lrwxrwxrwx 1 root root 0 Aug 4 15:13
consumer:platform:af00000.clock-controller ->
../../../virtual/devlink/platform:88e9000.phy--platform:af00000.clock-controller
-rw-r--r-- 1 root root 4096 Aug 4 15:13 driver_override
-r--r--r-- 1 root root 4096 Aug 4 15:13 modalias
lrwxrwxrwx 1 root root 0 Aug 4 15:13 of_node ->
../../../../firmware/devicetree/base/soc@0/phy@88e9000
drwxr-xr-x 2 root root 0 Aug 4 15:13 power
lrwxrwxrwx 1 root root 0 Aug 4 15:10 subsystem ->
../../../../bus/platform
lrwxrwxrwx 1 root root 0 Aug 4 15:13
supplier:platform:100000.clock-controller ->
../../../virtual/devlink/platform:100000.clock-controller--platform:88e9000.phy
lrwxrwxrwx 1 root root 0 Aug 4 15:13
supplier:platform:18200000.rsc:clock-controller ->
../../../virtual/devlink/platform:18200000.rsc:clock-controller--platform:88e9000.phy
lrwxrwxrwx 1 root root 0 Aug 4 15:13
supplier:platform:18200000.rsc:pm8150-rpmh-regulators ->
../../../virtual/devlink/platform:18200000.rsc:pm8150-rpmh-regulators--platform:88e9000.phy
-rw-r--r-- 1 root root 4096 Aug 4 15:10 uevent
-r--r--r-- 1 root root 4096 Aug 4 15:13
waiting_for_supplier
Thus it is not possible to spot this device link without
CONFIG_DEBUG_DRIVER=y (or any similar debugging technique).
I sent out some patches to make this easier. But doesn't look like
it'll land in 5.15.
https://lore.kernel.org/lkml/20210915172808.620546-1-saravanak@xxxxxxxxxx/
Thank you, I'll take a look.
If I re-enabled tcpm device or if I reverted remote-endpoint parsing, DP
PHY probing would go fine. The DP PHY does not really depend on the
connector (or TCPM) being present in the system. The driver will
continue working w/o it. However it does not have a change to declare that.
Furthermore I went back to the original case that caused you to add
remote-endpoint support. The DSI-eDP bridge and eDP panel using the GPIO
provided by that bridge. I think the proper fix for the original problem
was implemented by the commit bf73537f411b ("drm/bridge: ti-sn65dsi86:
Break GPIO and MIPI-to-eDP bridge into sub-drivers"). It split the
DSI-eDP bridge driver into functional parts (devices), so that GPIO part
and eDP parts are independent, thus breaking this cyclic dependency in a
functional way. The remote-endpoint parsing is no longer necessary in
this case (Stephen, please correct me if I'm wrong).
Even if the original case doesn't need remote-endpoint to work
correctly and the cycle has been broken, that doesn't remove the need
for parsing remote-endpoint. There could be other cases like the
original case.
I still think that remote endpoint parsing does more harm and noise than
good and thus should be reverted.
I'll agree to disagree. I'm sure your issue can be fixed without
removing support for remote-endpoint parsing -- let's work on that
(I've asked for more details above).
-Saravana
--
With best wishes
Dmitry