On Mon, Jul 19, 2021 at 12:36 PM Bjorn Andersson
[off-list ref] wrote:

On Mon 19 Jul 14:00 CDT 2021, John Stultz wrote:

quoted

On Fri, Jul 16, 2021 at 10:01 PM Bjorn Andersson
[off-list ref] wrote:

quoted

On Tue 06 Jul 23:53 CDT 2021, John Stultz wrote:

quoted

Allow the qcom_scm driver to be loadable as a permenent module.

This still uses the "depends on QCOM_SCM || !QCOM_SCM" bit to
ensure that drivers that call into the qcom_scm driver are
also built as modules. While not ideal in some cases its the
only safe way I can find to avoid build errors without having
those drivers select QCOM_SCM and have to force it on (as
QCOM_SCM=n can be valid for those drivers).

Reviving this now that Saravana's fw_devlink defaults to on,
which should avoid loading troubles seen before.

Are you (in this last paragraph) saying that all those who have been
burnt by fw_devlink during the last months and therefor run with it
disabled will have a less fun experience once this is merged?

Bjorn,

I jump in and help with any reports of issues with fw_devlink if I'm
cc'ed. Please feel free to add me and I'll help fix any issues you
have with fw_devlink=on.

quoted

I guess potentially. So way back when this was originally submitted,
some folks had trouble booting if it was set as a module due to it
loading due to the deferred_probe_timeout expiring.
My attempts to change the default timeout value to be larger ran into
trouble, but Saravana's fw_devlink does manage to resolve things
properly for this case.

Unfortunately I see really weird things coming out of that, e.g. display
on my db845c is waiting for the USB hub on PCIe to load its firmware,
which typically times out after 60 seconds.

I've stared at it quite a bit and I don't understand how they are
related.

Can you please add me to any email thread with the details? I'd be
happy to help.

First step is to make sure all the devices probe as with
fw_devlink=permissive. After that if you are still seeing issues, it's
generally timing issues in the driver. But if the actual timing issue
is identified (by you or whoever knows the driver seeing the issue),
then I can help with fixes or suggestions for fixes.

quoted

But if folks are having issues w/ fw_devlink, and have it disabled,
and set QCOM_SCM=m they could still trip over the issue with the
timeout firing before it is loaded (especially if they are loading
modules from late mounted storage rather than ramdisk).

I guess we'll have to force QCOM_SCM=y in the defconfig and hope people
don't make it =m.

quoted

quoted

(I'm picking this up, but I don't fancy the idea that some people are
turning the boot process into a lottery)

Me neither, and I definitely think the deferred_probe_timeout logic is
way too fragile, which is why I'm eager for fw_devlink as it's a much
less racy approach to handling module loading dependencies.

Right, deferred_probe_timeout is the main issue here. Without it we
might get some weird probe deferral runs, but either some driver is
missing or it settles eventually.

With deferred_probe_timeout it's rather common for me to see things
end up probe out of order (even more now with fw_devlink finding cyclic
dependencies) and deferred_probe_timeout just breaking things.

Again, please CC me on these threads and I'd be happy to help.

quoted

So if you
want to hold on this, while any remaining fw_devlink issues get
sorted, that's fine.  But I'd also not cast too much ire at
fw_devlink, as the global probe timeout approach for handling optional
links isn't great, and we need a better solution.

There's no end to the possible and valid ways you can setup your
defconfig and run into the probe deferral issues, so I see no point in
holding this one back any longer. I just hope that one day it will be
possible to boot the upstream kernel in a reliable fashion.

Might not be believable, but I'm hoping fw_devlink helps you meet this goal :)

-Saravana