On 1/26/21 8:14 AM, Leon Romanovsky wrote: > 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. I still have no idea *WHICH* device it was that the panic occurred on. > >> >>> 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 problematic due to out-of-date firmware or other issues.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. > See my answer below. I agree with you on the ABI statement. >> >>> >>>> >>>> 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. Yes, that's absolutely the case and I agree with you that nothing can guarantee ABI of those pr_debug() statements. They are *debug* after all. P. > > Thanks > >> >> P. >> >>> >>> Thanks >> >
