Re: [regression] nct6775 does not load in 5.4 and 5.5, bisected to b84398d6d7f90080

[Andy Shevchenko]

On Mon, Feb 24, 2020 at 12:18:00PM +0200, Mika Westerberg wrote:
> On Sat, Feb 22, 2020 at 01:26:48PM -0800, Guenter Roeck wrote:
> > On 2/22/20 12:49 PM, Martin Volf wrote:
> > > On Sat, Feb 22, 2020 at 8:05 PM Guenter Roeck <linux@xxxxxxxxxxxx> wrote:

...

> > >          devfn = PCI_DEVFN(PCI_SLOT(pci_dev->devfn), 2);

I'm wondering if

		pci_dev_is_present(...);

returns false here.

> > >          pci_bus_read_config_dword(pci_dev->bus, devfn, ACPIBASE, &base_addr);
> > > 
> > >          res = &tco_res[ICH_RES_IO_SMI];
> > >          res->start = (base_addr & ~1) + ACPIBASE_SMI_OFF;
> > >          res->end = res->start + 3;
> > >          res->flags = IORESOURCE_IO;
> > > 
> > > base_addr is 0xffffffff after pci_bus_read_config_dword() call.
> > > ACPIBASE_SMI_OFF is 0x030, therefore res->start is 0x2e.
> > > Not that I understand even a bit of this...
> > > 
> > 
> > Outch. This means that the code is broken. ACPIBASE is not configured,
> > or disabled, or the code reads from the wrong PCI configuration register.
> > What I don't understand is why this works with v5.3 kernels; the code
> > looks just as bad there for me. I must be missing something. Either case,
> > the only thing you can really do at this point is to blacklist the
> > iTCO_wdt driver.
> 
> Indeed it looks like the code reads from a register that is not there
> anymore in this generation hardware, or something like that. It tries to
> read the PMC (1f.2) register add address 0x40 which is supposed to be
> base of ACPI PM registers but that does not seem to exist any more in
> newer chipset.
> 
> We'll look into this more and return back.

-- 
With Best Regards,
Andy Shevchenko