On Mon, 1 Feb 2021, Thomas Gleixner wrote: > >> While it cures the problem on the reporters machine it breaks machines > >> with Intel chipsets which use bit 0-5 of the D register. So check only > >> for bit 6 being 0 which is the case on these Intel machines as well. > > > > This looks fine, but it might also be worth it simply just checking > > for the only really special value: 0xff, and going "ok, that looks > > like missing hardware". > > > > That's what a few other drivers historically do in their probing > > routines, so it's not unheard of (ie you can find drivers doing that > > kind of > > > > /* If we read 0xff from the LSR, there is no UART here. */ > > if (inb(.. port ..) == 0xff) > > > > in their init routines. > > > > Not a big deal either way, I just think it would be more in like with > > what other places do in similar situations > > Yeah, we can do that as well. Either way is fine. Given that evidently vendors appear to start playing with 146818 clones it may be worth it to peek at the D and the C register and checking they are not 0xff both at a time for robustness before concluding no RTC is present. The C register is supposed to hold zeros in bits 3:0. A read of the C register will drop interrupt bits, but I guess it does not matter at the probe time. FWIW, Maciej
