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

[Martin Volf]

Hello,

On Sat, Feb 22, 2020 at 8:05 PM Guenter Roeck <linux@xxxxxxxxxxxx> wrote:
> On 2/22/20 9:55 AM, Martin Volf wrote:
> > On Sat, Feb 22, 2020 at 4:41 PM Guenter Roeck <linux@xxxxxxxxxxxx> wrote:
> >> On 2/22/20 3:13 AM, Martin Volf wrote:
> >>> hardware monitoring sensors NCT6796D on my Asus PRIME Z390M-PLUS
> >>> motherboard with Intel i7-9700 CPU don't work with 5.4 and newer linux
> >>> kernels, the driver nct6775 does not load.
> >>>
> >>> It is working OK in version 5.3. I have used almost all released stable
> >>> versions from 5.3.8 to 5.3.16; I didn't try older kernels.
> > ...
> >> My wild guess would be that the i801 driver is a bit aggressive with
> >> reserving memory spaces, but I don't immediately see what it does
> >> differently in that regard after the offending patch. Does it work
> >> if you unload the i2c_i801 driver first ?
> >
> > Yes, after unloading i2c_i801, the nct6775 works.
...
> > This is diff of /proc/ioports in 5.3.18 with loaded nct6775 and in
> > 5.4.21 without:
> >
> > --- ioports-5.3.18
> > +++ ioports-5.4.21
> > @@ -2,6 +2,7 @@
> >     0000-001f : dma1
> >     0020-0021 : pic1
> >     002e-0031 : iTCO_wdt
> > +    002e-0031 : iTCO_wdt
> >     0040-0043 : timer0
> >     0050-0053 : timer1
...
> > So 0x2e is the resource the two drivers are fighting for.
...
> Yes, and it should not do that, since the range can be used to access
> different segments of the same chip from multiple drivers. This region
> should only be reserved temporarily, using request_muxed_region() when
> needed and release_region() after the access is complete. Either case,
> I don't immediately see why that region would be interesting for the
> iTCO watchdog driver.
>
> Can you add some debugging into the i801 driver to see what memory regions
> it reserves, and how it gets to reserve 0x2e..0x31 ? That range really
> doesn't make any sense to me.

in the function i801_add_tco() in drivers/i2c/busses/i2c-i801.c
(line 1601 in 5.4.21), there is this code:

        /*
         * Power Management registers.
         */
        devfn = PCI_DEVFN(PCI_SLOT(pci_dev->devfn), 2);
        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...

Martin