On 1/26/21 8:53 AM, Leon Romanovsky wrote: > On Tue, Jan 26, 2021 at 08:42:12AM -0500, Prarit Bhargava wrote: >> >> >> 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. > > The kernel panic is printed from the driver. There is one driver loaded > for all same PCI devices which are probed without relation to their > number.> > If you have host with ten same cards, you will see one driver and this > is where the problem and not in supported/not-supported device. That's true, but you can also have different cards loading the same driver. See, for example, any PCI_IDs list in a driver. For example, 10:00.0 RAID bus controller: Broadcom / LSI MegaRAID SAS-3 3008 [Fury] (rev 02) 20:00.0 RAID bus controller: Broadcom / LSI MegaRAID SAS-3 3108 [Invader] (rev 02) Both load the megaraid driver and have different profiles within the driver. I have no idea which one actually panicked until removing one card. It's MUCH worse when debugging new hardware and getting a panic from, for example, the uncore code which binds to a PCI mapped device. One device might work and the next one doesn't. And then you can multiply that by seeing *many* panics at once and trying to determine if the problem was on one specific socket, die, or core. > >>> >>>> >>>>> 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. > > You missed the point. ALL pr*() prints are not ABI, without relation to their level. > Yes, I understood that. I'm just emphasizing your ABI concern. P. > Thanks > >> >> P. >> >>> >>> Thanks >>> >>>> >>>> P. >>>> >>>>> >>>>> Thanks >>>> >>> >> >
