linux-kernel - Re: [RFC PATCH 0/2] Add a test to verify device probing on ACPI platforms

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Message-ID: <431009f0-56e7-46e8-a3a0-a8070554b727@suswa.mountain>
Date:   Thu, 23 Nov 2023 18:14:18 +0300
From:   Dan Carpenter <dan.carpenter@...aro.org>
To:     Laura Nao <laura.nao@...labora.com>
Cc:     broonie@...nel.org, groeck@...omium.org, kernel@...labora.com,
        kernelci@...ts.linux.dev, lenb@...nel.org,
        linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org, rafael@...nel.org,
        robh+dt@...nel.org, shuah@...nel.org
Subject: Re: [RFC PATCH 0/2] Add a test to verify device probing on ACPI
 platforms

On Thu, Nov 23, 2023 at 01:09:42PM +0100, Laura Nao wrote:
> > Your talk was interesting at Linux Plumbers.
> > 
> > https://www.youtube.com/watch?v=oE73eVSyFXQ [time +2:35]
> > 
> > This is probably a stupid question, but why not just add something to
> > call_driver_probe() which creates a sysfs directory tree with all the
> > driver information?
> > 
> 
> Thanks for the feedback! 
> 
> Improving the device driver model to publish driver and devices info
> was indeed another option we considered. We could have a debugfs entry
> storing this kind of information, similar to what devices_deferred
> does and in a standardized format. This would provide an interface
> that is easier to query at runtime for getting a list of devices that
> were probed correctly.
> This would cover devices with a driver that's built into the kernel or
> as a module; in view of catching also those cases where a device is
> not probed because the relevant config is not enabled, I think we'd
> still need another way of building a list of devices present on the
> platform to be used as reference.

Yeah.  So we'd still need patch #1 as-is and but patch #2 would probably
be simpler if we had this information in sysfs.  Or a different solution
would be to do what someone said in the LPC talk and just save the
output of the previous boot and complain if there was a regression where
something didn't probe.

> 
> The solution proposed in this RFC follows the same approach used for
> dt based platforms for simplicity. But if adding a new sysfs entry
> storing devices and driver info proves to be a viable option for
> upstream, we can surely explore it and improve the probe test to
> leverage that.

You're saying "simplicity" but I think you mean easiest from a political
point of view.  It's not the most simple format at all.  It's like
massive detective work to find the information and then you'll have to
redo it for DT and for USB.  Are there other kinds of devices which can
be probed?

I feel like you're not valuing your stuff at the right level.  This
shouldn't be in debugfs.  It should be a first class citizen in sysfs.

The exact format for this information is slightly tricky and people will
probably debate that.  But I think most people will agree that it's
super useful.

regards,
dan carpenter