linux-kernel - Re: [RFC PATCH 2/2] kselftest: devices: Add board file for google,spherion

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Date:   Fri, 27 Oct 2023 12:48:35 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Nícolas F. R. A. Prado 
        <nfraprado@...labora.com>
Cc:     Shuah Khan <shuah@...nel.org>, Bjorn Helgaas <bhelgaas@...gle.com>,
        devicetree@...r.kernel.org, linux-pci@...r.kernel.org,
        linux-usb@...r.kernel.org, Rob Herring <robh+dt@...nel.org>,
        linux-kselftest@...r.kernel.org, kernel@...labora.com,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 2/2] kselftest: devices: Add board file for
 google,spherion

On Wed, Oct 25, 2023 at 08:32:42AM -0400, Nícolas F. R. A. Prado wrote:
> On Wed, Oct 25, 2023 at 12:32:15PM +0200, Greg Kroah-Hartman wrote:
> > On Tue, Oct 24, 2023 at 05:18:00PM -0400, Nícolas F. R. A. Prado wrote:
> > > Add the list of devices expected to be probed from the USB and PCI
> > > busses on the google,spherion machine. The USB host controller at
> > > 11200000 is shared between two busses, for USB2 and USB3, so an
> > > additional match is used to select the USB2 bus.
> > > 
> > > Signed-off-by: Nícolas F. R. A. Prado <nfraprado@...labora.com>
> > > ---
> > > 
> > >  tools/testing/selftests/devices/boards/google,spherion | 3 +++
> > >  1 file changed, 3 insertions(+)
> > >  create mode 100644 tools/testing/selftests/devices/boards/google,spherion
> > > 
> > > diff --git a/tools/testing/selftests/devices/boards/google,spherion b/tools/testing/selftests/devices/boards/google,spherion
> > > new file mode 100644
> > > index 000000000000..ba86ffcfe43c
> > > --- /dev/null
> > > +++ b/tools/testing/selftests/devices/boards/google,spherion
> > > @@ -0,0 +1,3 @@
> > > +usb camera 11200000,PRODUCT=.*/2/.* 1.4.1 1 0,1
> > > +usb bluetooth 11200000,PRODUCT=.*/2/.* 1.4.2 1 0,1
> > > +pci wifi 11230000 0.0/0.0
> > 
> > USB busses (and PCI ids) are not determinisitic and can, and will,
> > change values randomly.  So while it is nice to test "did the devices
> > show up properly", you can not do that based on bus ids at all, sorry.
> > 
> > Unless I'm reading these values wrong?  What are the fields
> > representing?  Perhaps a comment at the top to describe them so that we
> > know how to parse them?
> 
> Hi Greg,
> 
> I have described the fields in the commit message of patch 1. Here they are:
> 
> usb <test_name> <controller_address>[,<additional_match>] <ports_path> <configuration> <interfaces>
> 
> pci <test_name> <controller_address> <device-function_pairs_path>

That's not a good place to document them, we'll never find them, and I
obviously missed it as well.

Please put it in a comment at the top of this file _AND_ in a comment in
the script that parses these files.

> I'm aware that bus IDs are assigned at runtime, and that's exactly why I've
> avoided those in the test definitions, instead describing the hardware topology,
> which won't ever change.
> 
> And just to be extra clear, by hardware topology I mean:
> 
> For USB, we find the USB bus based on the address of its controller (and
> optionally its productID if two busses share the same controller for USB2 and
> USB3),

What exactly do you mean by "address" of a controller?  That will be
unique per bus-type that the controller lives on, right?

> and then find the device by following the ports at each hub. The
> configuration number and interfaces then describe what interfaces to check for
> presence and driver binding.

Ok, good, hub and port locations _should_ be stable, but note they have
changed at times so you will have to deal with that for the next 20+
years, are you ok with that?

> For PCI, we find the controller again based on its address, and follow the
> device-function pairs at each level in the topology until we arrive at the
> desired device.

"address"?  What exactly do you mean by this value?  For PCI, that will
change.

> We don't rely on the USB bus number, nor on the PCI domain and bus number, since
> these are all assigned at runtime.

You are relying on a specific sysfs tree as well, are you able to handle
it when new devices get added to the middle of a device path?  That
sometimes happens in sysfs too.

thanks,

greg k-h