Leon Romanovsky <leon@xxxxxxxxxx> 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 problematic due to out-of-date firmware or other issues.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
