On Tue, Jan 26, 2021 at 07:54:46AM -0500, Prarit Bhargava wrote: > 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. How? If you have kernel panic, it means you have much more worse problem than not-supported device. If kernel panic was caused by the driver, you will see call trace related to it. If kernel panic was caused by something else, supported/not supported won't help here. > > > 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 problematic due to out-of-date firmware or other issues.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... You will need much more stronger claim than the above if you want to proceed ABI path through dmesg prints. > > > > > > > > > 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. Just to be clear, none of this can be ABI and any kernel print can be changed or removed any minute without any announcement. Thanks > > P. > > > > > Thanks >
