Re: [PATCH] pci-driver: Add driver load messages

[Prarit Bhargava <prarit@redhat.com>]

  Leon Romanovsky <leon@kernel.org> wrote:
> On Mon, Jan 25, 2021 at 02:41:38PM -0500, Prarit Bhargava wrote:
> > There are two situations where driver load messages are helpful.
> >
> > 1) Some drivers silently load on devices and debugging driver or system
> > failures in these cases is difficult.  While some drivers (networking
> > for example) may not completely initialize when the PCI driver probe() function
> > has returned, it is still useful to have some idea of driver completion.
> 
> Sorry, probably it is me, but I don't understand this use case.
> Are you adding global to whole kernel command line boot argument to debug
> what and when?
> 
> During boot:
> If device success, you will see it in /sys/bus/pci/[drivers|devices]/*.
> If device fails, you should get an error from that device (fix the
> device to return an error), or something immediately won't work and
> you won't see it in sysfs.
> 

What if there is a panic during boot?  There's no way to get to sysfs.
That's the case where this is helpful.

> During run:
> We have many other solutions to get debug prints during run, for example
> tracing, which is possible to toggle dynamically.
> 
> Right now, my laptop will print 34 prints on boot and endless amount during
> day-to-day usage.
> 
> ➜  kernel git:(rdma-next) ✗ lspci |wc -l
> 34
> 
> >
> > 2) Storage and Network device vendors have relatively short lives for
> > some of their hardware.  Some devices may continue to function but are
> > problematic due to out-of-date firmware or other issues.  Maintaining
> > a database of the hardware is out-of-the-question in the kernel as it would
> > require constant updating.  Outputting a message in the log would allow
> > different OSes to determine if the problem hardware was truly supported or not.
> 
> And rely on some dmesg output as a true source of supported/not supported and
> making this ABI which needs knob in command line. ?

Yes.  The console log being saved would work as a true source of load
messages to be interpreted by an OS tool.  But I see your point about the
knob below...

> 
> >
> > Add optional driver load messages from the PCI core that indicates which
> > driver was loaded, on which slot, and on which device.
> 
> Why don't you add simple pr_debug(..) without any knob? You will be able
> to enable/disable it through dynamic prints facility.

Good point.  I'll wait for more feedback and submit a v2 with pr_debug.

P.

> 
> Thanks